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Old 04-12-2019, 11:29 PM   #1
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House & Start Bank Design Issue

I want to wire my 200a (continuous-rated) alternator directly (with a fuse of course) to my 12v 900Ah House bank, then automate the charging connection to my 12v/24v 220Ah Start bank. Both banks have the same charging profile.

The unusual issue is that the Start bank (2xG31) is normally in 12v (parallel) configuration, but will go into 24v (series) configuration via a heavy contactor when the bow thruster is 'Activated' by a manual switch in the wheelhouse. After the thruster is de-activated, the Start bank goes back (contactor relaxes) to its normal 12v configuration for charging, engine & generator start, and windlass use.

The way the boat builder (KK) afaik dealt with the voltage disparity/bank separation issue is to have an Alternator Output Selector Switch (AOSS) manually switched between either the House or Start banks, or Both banks combined. So the boat operator MUST remember to never activate the bow thruster when the two banks are combined. Also don't try to start the engine or generator, or run the windlass when the bow thruster is activated. This system has potential for fireworks , so I want to improve it.

The attached drawing shows three possibilities. All are meant to go where the boxes with question marks are in the drawing. I'm using 4/0 in that line for an emergency engine start if Start bank was critically discharged.

Regarding possibility #2, I have an inquiry into Sterling-Power-USA whether the PSR252 https://www.sterling-power-usa.com/P...solator-6.aspx will withstand the Start bank in 24v configuration trying to backfeed to the 12v House bank. If it can, that seems simplest and most reliable way to do this. And it doesn't have the inefficiency/voltage drop issues of regular battery isolators.

The Blue Sea ACR (will close when charging voltage at House bank is present) and RBS (will open when bow thruster is activated) seem a bit busy (less reliable?), and the heavy diode & DC to DC charger (to deal with diode voltage drop) seem lossy and clumsy.

This is a situation I haven't dealt with before, so any constructive advice or out of the box thinking would be most appreciated.
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Old 04-13-2019, 12:14 AM   #2
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I thought Blue Sea made combiners with overvoltage protection? These will disconnect both below and above a certain voltage. I don't know that I'd depend on that routinely, but it might be a solution to operator forgetfulness.
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Old 04-13-2019, 07:14 AM   #3
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I'm presuming the thruster is in the bow, and the batteries are some distance away. My boat was set up OEM in a similar way from what I can determine from artifacts/old wiring. Now, the thruster batteries are in the bow, and there is a dedicated 24V smart charger adjacent. The batteries are Optimas. It works splendidly, not too long ago I added the smart charger to the inverter load, as there was no means to charge the thruster bank under way. It has worked out very well, I can switch off the charger while at anchor to reduce the load on the inverter bank.

I have a start battery, but in reality, there's no reason for it. The house bank would easily start the main even at 50% SoC. But that's the way it was and it was easy enough to just keep the configuration.

In your case, would it not be easier to just move the firefly batteries close to the thruster, and either add a smart charger, or use a 12V-24V converter to charge the bank from the 12V system? Start the mains from the house bank. I'd think that eliminating the relays that create the 24V would be preferable since there's potential to expose the 12v system to 24V in the event of a relay malfunction. I'm aware that running a battery charger from an inverter carries loss penalties, but if you're under way and have a 200A alternator powering the inverter, the loss issue is really moot. The 24V charger would not need to be high amperage, the thruster bank can recharge at a low rate without concern. At anchor, there's no need to charge the thruster bank, it can charge when the genset is running.



WRT windlass, you already have cabling, could you not just power that from the house? It would probably not be upset with the long run, may reduce speed a bit, but should not impact power. It doesn't behave the same as an AC inductive motor in that regard. Charge the house from the alternator, preferable in any event.


Having the thruster bank close to the thruster would probably allow the thruster to run a bit faster without the voltage drop in the long wire run. You already have the batteries. You just don't want to have fire fly from the Firefly's. Nyuk, nyuk

Out of the box?
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Old 04-13-2019, 07:19 AM   #4
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Why don't you put a pair of sealed batteries in series in the bow thruster area, use a 6 amp smart charger off your inverter to maintain them, and eliminate all the complexities and long cable runs? That is what I did on my boat, and it's worked perfectly for 3+ years.

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Old 04-13-2019, 08:52 AM   #5
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Quote:
Originally Posted by O C Diver View Post
Why don't you put a pair of sealed batteries in series in the bow thruster area, use a 6 amp smart charger off your inverter to maintain them, and eliminate all the complexities and long cable runs? That is what I did on my boat, and it's worked perfectly for 3+ years.

Ted

+1


Your existing system is archaic and somewhat dangerous. As noted above, separate the 12V and 24V loads and charge the 24V with a small smart charger or maybe a DC to DC charger so it can also be charged from the alternator. If you already have the big wiring in place and can find a place for a couple of batteries near the 12V ones then you can install them there.


There was a recent thread asking whether a bow thruster requires a starting or deep cycle battery. I and most others believe that a bow thruster is closer to a high current starting load than a long term deep cycle load. So use a couple of starting batteries. Two Group 27 or 31 starting batteries should handle your bow thruster fine.


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Old 04-13-2019, 09:07 AM   #6
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As Ted and David suggest, two forward mounted 12v (AGMs maybe) batteries setup for 24v is the way to go.
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Old 04-13-2019, 11:14 AM   #7
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Hah!, great pun Steve.

The battery banks are both amidships with long cable runs to the bow for 12v windlass and 24v bow thruster. The original Sprint 1500 windlass is tired and kinda puny, so I'm looking into replacing it with a bigger 24v V3 unit.

Well gentlemen, looks like we have a Guru consensus--two batteries in the bow. Thank you. It will mean some serious fibreglass work to create a strong, solid battery holding compartment. Lotta movement and shock loads in bad weather. The only place there's room is under our bed in the master stateroom. We live on our one-stateroom boat, so have logistical issues installing the battery box. Gotta mull it over.

BTW, one of the cool features of Fireflys is they act like both start and deep cycle batteries. Plenty of surge current for thruster/engine start operations. Very low self-discharge rate. No real PSOC issues. I left my FF L15+ house bank uncharged for ~1yr. and it was only down about 10-15%. Came right back with the FF 'battery stretching' charge procedure.
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Old 04-13-2019, 11:17 AM   #8
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This calls for a professional...

Quote:
Originally Posted by Wil View Post
I want to wire my 200a (continuous-rated) alternator directly (with a fuse of course) to my 12v 900Ah House bank, then automate the charging connection to my 12v/24v 220Ah Start bank. Both banks have the same charging profile.

The unusual issue is that the Start bank (2xG31) is normally in 12v (parallel) configuration, but will go into 24v (series) configuration via a heavy contactor when the bow thruster is 'Activated' by a manual switch in the wheelhouse. After the thruster is de-activated, the Start bank goes back (contactor relaxes) to its normal 12v configuration for charging, engine & generator start, and windlass use.

The way the boat builder (KK) afaik dealt with the voltage disparity/bank separation issue is to have an Alternator Output Selector Switch (AOSS) manually switched between either the House or Start banks, or Both banks combined. So the boat operator MUST remember to never activate the bow thruster when the two banks are combined. Also don't try to start the engine or generator, or run the windlass when the bow thruster is activated. This system has potential for fireworks , so I want to improve it.

The attached drawing shows three possibilities. All are meant to go where the boxes with question marks are in the drawing. I'm using 4/0 in that line for an emergency engine start if Start bank was critically discharged.

Regarding possibility #2, I have an inquiry into Sterling-Power-USA whether the PSR252 https://www.sterling-power-usa.com/P...solator-6.aspx will withstand the Start bank in 24v configuration trying to backfeed to the 12v House bank. If it can, that seems simplest and most reliable way to do this. And it doesn't have the inefficiency/voltage drop issues of regular battery isolators.

The Blue Sea ACR (will close when charging voltage at House bank is present) and RBS (will open when bow thruster is activated) seem a bit busy (less reliable?), and the heavy diode & DC to DC charger (to deal with diode voltage drop) seem lossy and clumsy.
Quote:
Originally Posted by Wil View Post
This is a situation I haven't dealt with before, so any constructive advice or out of the box thinking would be most appreciated.
Kudos on choosing the Firefly's -- Carbon Foam is the best possible choice for this application. Also, using 6 x 2volt cells for your house bank -- very smart! You can carry a spare so when a cell goes bad, you just replace the one that failed.

Re: "The unusual issue is that the Start bank (2xG31) is normally in 12v (parallel) configuration, but will go into 24v (series) configuration via a heavy contactor when the bow thruster is 'Activated' by a manual switch in the wheelhouse. After the thruster is de-activated, the Start bank goes back (contactor relaxes) to its normal 12v configuration for charging, engine & generator start, and windlass use."

Re: "This system has potential for fireworks , so I want to improve it."

Yes, it certainly does. Wow...this is quite dangerous. I'd be surprised if this was designed by KK. I am wondering if the thruster was added after the fact...on-the-cheap...by a bonehead. Or maybe the selling dealer did it? Perhaps they used a 24v thruster because it can use smaller gauge (cheaper) wire for the same horsepower, and sometimes this is necessary when the length of the wiring is too long for 12v, but I doubt this is the case for you. Also, some of the largest thrusters (20hp and up) might only be available in 24v (or as hydraulics), but I doubt this is the case on a KK39.

First off...someone has the original factory wiring diagrams for your boat. I've worked on a few over the years and at least the larger/newer ones will have a hull# specifc owners manual with as-delivered options shown on the wiring diagram.


If you don't have it in your owners manual, try to get it. If the thruster wiring diagram for a 24v thruster is not shown, KK will have had an ABYC compliant option for a factory installed bow thruster, and they will be able to tell you how it should be done, and even if it CAN be done on your boat with a 24v thruster. Their design would have gone through a lot of scrutiny by their engineers to meet ABYC standards. The original KK design is the only design I would use, if you can find it.

That said...this is a complicated scenario. If you are going to try to reuse ANY of the current setup, and you can't get the design from KK, then you really need to hire an ABYC certified tech who has E-11 and (if you want to install new batteries/chargers in other-than-factory-designated-locations), also have E-10 and A-31 certs. Real certifications. Many 'marine electricians' might be ABYC members, few are actually certified.

Re: "the Start bank (2xG31) is normally in 12v (parallel) configuration"

Right there is your disaster waiting to happen...curious...did your pre-purchase surveyor look at this at all?

Now...by my read of the standards, a 24v thruster in a 12v system could work like this:
  • 2xG31s NOT (never) in parallel except for emergency starting. The paralleling switch MUST be a solenoid-type momentary contact switch and NOT a manual switch that can accidently be left in parallel mode (which you say you have). This is yet another clue that this was a bonehead-hack job. That solenoid switch is expensive ($400), the manual switch is $30.
  • Bow thruster neg attached to the main ground bus (engine block?), thruster positive attached to the #2 G31.
  • On operating the thruster, batteries are momentarily placed in series, giving you 24V for the thruster. To do this, the ground for the #2 G31 (only) needs to be momentarily disconnected, and simultaneously connected to the pos terminal of the #1 using yet another ~$400 solenoid switch.
  • This way, the #1 G31 (being the 'main' source of 12v) is still providing 12v to everything that needs to stay alive. There should NOT be any interruption to your 12V supply to anything on the boat when using the thruster.
So, by my count there must be a minimum of three solenoid switches -- and they won't come cheap. At 24v and (guessing) 95kW or higher, the solenoids will need to be ~400A, and they will need to be ignition protected types. Even with the solenoids, this setup is dicey.


There are other ways one could do it, but I think the number of solenoids will be the same.


Re: "out of the box thinking"

Hmmm...depending on who made that thruster, you SHOULD be able to replace the 24v motor unit with a 12v motor. Depending on the size of the existing wiring running up there, you might need to upsize it, and you'd need to use larger over-current protection, but this could be cheaper than trying to 'fix' the apparent kludge you have now. No matter what you do, switching to a 12v motor would result in a much simpler and safer system. Personally, I'd rather spend the money on switching it over to 12v than creating a better kludge than the kludge you have...

Hopefully this makes sense...but PLEASE DO get professional help here. If something very bad happens, and you have touched it in ANY way...your insurance company will have an "out" to deny a claim.
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Old 04-13-2019, 11:53 AM   #9
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Riverguy,
A friendly word of advice. Your posts at times come across as condescending. There are many of us on TF that are marine professionals with years or decades of experience that are willing to share their knowledge with others, for free. Pointing out advice that is dangerous is one thing, badmouthing other members because you think you have a better idea is another.

As far as the OP, the advice that several others gave you of a seperate 24v bank and charger is good, solid advice, and probably the simpliest solution. That is what we have on our KK.
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Old 04-13-2019, 11:55 AM   #10
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Be careful...

Quote:
Originally Posted by O C Diver View Post
Why don't you put a pair of sealed batteries in series in the bow thruster area, use a 6 amp smart charger off your inverter to maintain them, and eliminate all the complexities and long cable runs? That is what I did on my boat, and it's worked perfectly for 3+ years.

Ted
Re: "and eliminate all the complexities and long cable runs?"

If this was a new install, that might make sense. However, in this case the wiring for the bow thruster is already there, so why go to the work and trouble? The complexity (and dangers) in this system appear to be in the 12v<->24v switching, according to the OP.

Re: "use a 6 amp smart charger off your inverter to maintain them"

Problem...the batteries bank will be 220Ah. Batteries need to be charged from time to time at around 10% of their Amp-Hour rating (minimum) to de-sulfate, in this case that would be 22A. 6A will not be enough. Maybe the Carbon Foam batteries Wil is using are more tolerant, but I don't think so.

Also...I'm concerned about impressed-current corrosion. The system you describe can have a different ground/galvanic potential than the rest of the boat. Care needs to be used to make sure you're not creating impressed-current corrosion.

Personally, for a new thruster install I'd do this:

https://www.bluesea.com/support/arti...atteryLink_ACR

Unfortunately, Wil has a 24v thruster.
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Old 04-13-2019, 12:48 PM   #11
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House &amp; Start Bank Design Issue

Quote:
Originally Posted by Riverguy View Post
Also...I'm concerned about impressed-current corrosion. The system you describe can have a different ground/galvanic potential than the rest of the boat. Care needs to be used to make sure you're not creating impressed-current corrosion.

Iím interested in your comments here. Exactly what is impressed current corrosion? Should the bonding system on the bow thruster be isolated from the rest of the boat? The reason I am asking is, the prop sacrificial anodes on my bow thruster (24 VDC) deteriorate more rapidly than those on the rudder and running gear prop. Iím concerned that these ďsac anodesĒ are running down more rapidly because they are offering disproportionate protection to the rest of the vesselís bonding system.

Jim
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Old 04-13-2019, 12:57 PM   #12
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Series parallel explanation

Taken a few minutes to put this together. Let me know if it makes sense:

The thruster battery bank should not back feed 24-volts to your other system. The only place that will see 24-volts is the output of the series/parallel switch. You can prove this by monitoring the voltage where the current charging leads attach while running the thruster. You will only see 12-volts. However, if the charging leads positive is on one battery and the negative on other then a short circuit will occur which you should be able to remedy.

I have attached a diagram that explains this. The series parallel switch has the batteries in parallel when at rest and in series when making 24-volts. If you look at the circuit you will see only the positive and negative of one battery should be connected to the engine starter (charging source) when the system is in parallel.

Properly connected the only thing that may happen is the batteries will go slightly out of balance since only one of the pair will be charging as the thruster is in use if wired the same as the diagram. This should resolve itself in short order once the thruster is put back to rest.

Quote:
Originally Posted by Wil View Post
I want to wire my 200a (continuous-rated) alternator directly (with a fuse of course) to my 12v 900Ah House bank, then automate the charging connection to my 12v/24v 220Ah Start bank. Both banks have the same charging profile.

The unusual issue is that the Start bank (2xG31) is normally in 12v (parallel) configuration, but will go into 24v (series) configuration via a heavy contactor when the bow thruster is 'Activated' by a manual switch in the wheelhouse. After the thruster is de-activated, the Start bank goes back (contactor relaxes) to its normal 12v configuration for charging, engine & generator start, and windlass use.

The way the boat builder (KK) afaik dealt with the voltage disparity/bank separation issue is to have an Alternator Output Selector Switch (AOSS) manually switched between either the House or Start banks, or Both banks combined. So the boat operator MUST remember to never activate the bow thruster when the two banks are combined. Also don't try to start the engine or generator, or run the windlass when the bow thruster is activated. This system has potential for fireworks , so I want to improve it.

The attached drawing shows three possibilities. All are meant to go where the boxes with question marks are in the drawing. I'm using 4/0 in that line for an emergency engine start if Start bank was critically discharged.

Regarding possibility #2, I have an inquiry into Sterling-Power-USA whether the PSR252 https://www.sterling-power-usa.com/P...solator-6.aspx will withstand the Start bank in 24v configuration trying to backfeed to the 12v House bank. If it can, that seems simplest and most reliable way to do this. And it doesn't have the inefficiency/voltage drop issues of regular battery isolators.

The Blue Sea ACR (will close when charging voltage at House bank is present) and RBS (will open when bow thruster is activated) seem a bit busy (less reliable?), and the heavy diode & DC to DC charger (to deal with diode voltage drop) seem lossy and clumsy.

This is a situation I haven't dealt with before, so any constructive advice or out of the box thinking would be most appreciated.
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File Type: pdf Thruster series parallel switch diagram.pdf (89.2 KB, 23 views)
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Old 04-13-2019, 01:02 PM   #13
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Quote:
Originally Posted by Stripper View Post
Riverguy...advice...
1) Wil identified his present setup as dangerous and he's right. It's messed up and SOMEBODY who was grossly incompetent kludged it.

2) I didn't identify any specific person...so who is getting 'badmouthed' (besides me, by you)?

3) I didn't say creating a separate bank or moving his batteries forward was 'wrong' and I didn't dispute that idea. Rereading the OP, I think he's identified the problem and he's on the right track...without moving the batteries or building a seperate bank. He just needs to fix the paralleling switch issue.

Re: "There are many of us on TF that are marine professionals with years or decades of experience that are willing to share their knowledge with others, for free."

Certainly, that's why people come here. But there are also many here that have kludged together dangerous solutions that they're quite proud of because it saved them money. How to know the difference?

Given what I have seen over more than 30 years in the industry (including what we all just saw was done on Wil's boat), I find that professional incompetence is rampant, and nowhere is this more true than in electrical systems. Are you suggesting it's not?

I'm sorry if that feels condescending to you, but not sure why it would, it wasn't directed at you. In fact, you didn't even offer a solution here, so clearly my comments weren't about you.

My post was for the person who asked the question. If I got something wrong, let me know.

Thanks.
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Old 04-13-2019, 01:44 PM   #14
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Wasnít badmouthing or finding fault with your posts. Maybe it is just me but I read your posts and read it as condescending. I like to give people the benefit of the doubt and hoped that is not the intention here. I guess if it is just me I should have PMed you instead.
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Old 04-13-2019, 02:02 PM   #15
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Quote:
Originally Posted by Riverguy View Post
Re: "and eliminate all the complexities and long cable runs?"

If this was a new install, that might make sense. However, in this case the wiring for the bow thruster is already there, so why go to the work and trouble? The complexity (and dangers) in this system appear to be in the 12v<->24v switching, according to the OP.
You answered your own question, archaic design with inherent problems (complicated switching design and unreasonable voltage drop reducing performance).



Quote:
Originally Posted by Riverguy View Post
Re: "use a 6 amp smart charger off your inverter to maintain them"

Problem...the batteries bank will be 220Ah. Batteries need to be charged from time to time at around 10% of their Amp-Hour rating (minimum) to de-sulfate, in this case that would be 22A. 6A will not be enough. Maybe the Carbon Foam batteries Wil is using are more tolerant, but I don't think so
Do the math (I did) on on watts consumed in typical bow thruster maneuvers. As they are extremely time / heat limited, a deep cycle battery is inappropriate for this application. A start battery with CCA is called for. As very little energy is drawn from the battery (it's all about CCA), the charger operates in float or at most absorption. Unlikely the battery drops below 90% of full charge. Finally, proof is in the testing. Did the Great Loop solo with the boat (single engine and bow thruster). Don't know if you can fathom how many bow thruster pulses and battery cycles for all the locks and docking. System works flawlessly!


Quote:
Originally Posted by Riverguy View Post
Also...I'm concerned about impressed-current corrosion. The system you describe can have a different ground/galvanic potential than the rest of the boat. Care needs to be used to make sure you're not creating impressed-current corrosionlll
That's why you use a marine battery charger with proper isolation and the bow thruster manufacturers electrically isolate the motor from the lower unit in the tunnel.

Quote:
Originally Posted by Riverguy View Post

Personally, for a new thruster install I'd do this:

https://www.bluesea.com/support/arti...atteryLink_ACR

Unfortunately, Wil has a 24v thruster.
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Old 04-13-2019, 02:59 PM   #16
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Quote:
Originally Posted by JDCAVE View Post
Iím interested in your comments here. Exactly what is impressed current corrosion? Should the bonding system on the bow thruster be isolated from the rest of the boat? The reason I am asking is, the prop sacrificial anodes on my bow thruster (24 VDC) deteriorate more rapidly than those on the rudder and running gear prop. Iím concerned that these ďsac anodesĒ are running down more rapidly because they are offering disproportionate protection to the rest of the vesselís bonding system.

Jim
JD
How long does your thruster zinc last in comparison to others on your vessel?

My stern plate last for about 3 seasons. My shaft zincs 5-7 months. Genset zinc 12 months and on and on. It is not uncommon on land or sea to have differential anode wear. Metal surface area, mass, location and other factors play into it.
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Old 04-13-2019, 04:42 PM   #17
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Quote:
Originally Posted by bglad View Post
Taken a few minutes to put this together. Let me know if it makes sense:

The thruster battery bank should not back feed 24-volts to your other system. The only place that will see 24-volts is the output of the series/parallel switch. You can prove this by monitoring the voltage where the current charging leads attach while running the thruster. You will only see 12-volts. However, if the charging leads positive is on one battery and the negative on other then a short circuit will occur which you should be able to remedy.

I have attached a diagram that explains this. The series parallel switch has the batteries in parallel when at rest and in series when making 24-volts. If you look at the circuit you will see only the positive and negative of one battery should be connected to the engine starter (charging source) when the system is in parallel.

Properly connected the only thing that may happen is the batteries will go slightly out of balance since only one of the pair will be charging as the thruster is in use if wired the same as the diagram. This should resolve itself in short order once the thruster is put back to rest.
Thanks BGlad for the diagram...helps with the discussion. This is almost exactly the solution I described earlier. The entire manual for this device (Side-Power PR100) is attached. It's got 2 solenoids in it for about $1,100.

Re: "If you look at the circuit you will see only the positive and negative of one battery should be connected to the engine starter (charging source) when the system is in parallel."

That's not how I read it. Looking at the wire labled "RED 16", this wire keeps the batteries in parallell all the time until the moment you engage the thruster. Now...walking it through...if you have both battery switches on (and solenoids are not energized), then cranking the engine will use both batteries, because they are always in parallel. However, if you have Battery1 turned off and Battery2 turned on, you will wind up cranking your engine solely with Battery2 via "red 16" and also through it's overcurrent device. That means that RED16 needs to be as large as the main cranking motor wire and that the overcurrent device (with thrusters, it's usually a fuse) needs to not blow when you crank the engine. Not liking this so much...

Now....let's say I've left Battery2 "off" (and fully charged) and then run battery 1 way down, or maybe it's dead. Now I turn battery2 on and we get an enormous current inrush into battery 1, which is not good. ABYC E-10 deals with this (10.5.4.1) by requiring a charge equalizer in this installation.

I think Wil is going to want to use three solenoids. I can't see any other solution. The third solenoid puts the batteries in parallel when needed, but only when needed. It could be implemented (and would be ABYC compliant) with the Side-Power box and a charge equalizer.
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Old 04-13-2019, 05:08 PM   #18
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...and unreasonable voltage drop reducing performance)...
Re: "...unreasonable voltage drop reducing performance)".

Looking at the O.P. and comments -- I have not seen any reference to voltage drop problems. I would be surprised if there were any with a 24v thruster. A 24v thruster needs only half as much current for the same power -- and this is huge because of I-squared-R. Doing the math...a 24v thruster that pulls 200A has the same power as a 12v thruster pulling 400a, but because current gets squared in the wire sizing calculation, we find that we can wire up the 24v thruster with AWG 2, but you need to go MUCH larger (all the way to AWG 4/0) to wire up the 12v thruster for 400A.

It is counter-intuitive, but going from 12-24 volts means you only need 25% as much copper to wire it up.

Re: "Do the math (I did) on on watts consumed in typical bow thruster maneuvers. As they are extremely time / heat limited, a deep cycle battery is inappropriate for this application."

I didn't say anything about starting vs. deep-cycle, but you are correct, deep-cycle batteries are not the right choice here. I didn't know there was a debate over that. The problem I referred to is sulfation. A 6A charger is not big enough to de-sulfate the plates.

In any case...there is hardly a good reason to move the batteries when we have a 24v thruster and the long wires are already in place. Just need to fix the series/parallel switching.
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Old 04-13-2019, 05:33 PM   #19
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Quote:
Originally Posted by Riverguy View Post
Re: "...unreasonable voltage drop reducing performance)".

Looking at the O.P. and comments -- I have not seen any reference to voltage drop problems. I would be surprised if there were any with a 24v thruster. A 24v thruster needs only half as much current for the same power -- and this is huge because of I-squared-R. Doing the math...a 24v thruster that pulls 200A has the same power as a 12v thruster pulling 400a, but because current gets squared in the wire sizing calculation, we find that we can wire up the 24v thruster with AWG 2, but you need to go MUCH larger (all the way to AWG 4/0) to wire up the 12v thruster for 400A.

It is counter-intuitive, but going from 12-24 volts means you only need 25% as much copper to wire it up.

Re: "Do the math (I did) on on watts consumed in typical bow thruster maneuvers. As they are extremely time / heat limited, a deep cycle battery is inappropriate for this application."

I didn't say anything about starting vs. deep-cycle, but you are correct, deep-cycle batteries are not the right choice here. I didn't know there was a debate over that. The problem I referred to is sulfation. A 6A charger is not big enough to de-sulfate the plates.

In any case...there is hardly a good reason to move the batteries when we have a 24v thruster and the long wires are already in place. Just need to fix the series/parallel switching.
Maybe you should measure the voltage at your thruster when it's running. As voltage drops on a DC motor, RPM decreases, the thruster heats up faster, and duty cycle shortens. On my boat, the cable runs to the thruster were probably 25 to 30' (total length 50 to 60'). Significant voltage drop. Now, the total cable length (out and back) is about 7'.

Ted
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Old 04-13-2019, 05:54 PM   #20
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At the risk of being chastised for not reading the OP intent. When I rewired the kids commercial boat it had a 12v house system and a 24 v starter. I used a relay similar to this 12/24 Volt DC 1500 amp Series Parallel Solenoid Relay. to provide 24 v to the starter. We fed the 12v from the alternator to the house bank and charged the starter batts with a blue seas ACR with starter isolation. this opens the acr when the starter relay is energized. This basically the same system that was used on our Defever's bow thruster ironically the stern thruster used its own dedicated 24 volt batteries with a dedicated charger. So we had both systems and neither failed.
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