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Old 10-19-2013, 09:06 AM   #1
gar
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Bow Thruster problem

Hi All, I just had a new electric thruster installed. My old on needed the motor rebuilt & it was just more cost effective to replace entire unit. The old unit would not rev very high and would quickly drop the volt meter below 10 volts. The new unit really is powerful and moves the bow strongly. Problem is this unit after 3-4 short bursts of power drops the voltage to 10volt & runs very slow, just like the old one. I had the wiring & batteries checked & all checked out well. I have 2 group 31s on 2 banks. I am going to replace the alternator, as it is getting weak. My question is should not 2 new group 31 batteries be able to power the unit with out the help of the alternator? Nominal thruster amp draw is 350 cca and my batteries far exceed this.
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Old 10-19-2013, 09:41 AM   #2
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[QUOTE=gar;185621] Hi I had the wiring & batteries checked & all checked out well. I have 2 group 31s on 2 banks. By the same group that sold you a thruster motor? [QUOTE]

How old are the batteries and how was the check done? A load test should be performed. although it sounds like your thruster is already doing one. Whoever installed your new thruster should be able to determine the problem, if not you have discovered the problem - the installer.
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Old 10-19-2013, 09:46 AM   #3
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My question is should not 2 new group 31 batteries be able to power the unit with out the help of the alternator?
Are you running the thruster without the engine on and, thus, no alternator output?
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Old 10-19-2013, 12:23 PM   #4
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I am not sure what time limit is assigned to the rating of CCAs.....but I would imagine it is quite short. Most likely, the issue here is not the batteries....it is the wiring and the distance of the wire run. I am going to guess that the batteries are somewhere in the engine room a pretty good distance from the thruster??? I already know that is the answer. And your solution would be to put a battery up in the bow right next to the thruster. And just 1 group 31 would do a dandy job in that application.

The only reason I say all of this is that is what my thruster used to do....even after installing brand new AGM batteries. Your thruster is(was) not faulty. You were just losing too much voltage over the wiring.

The reason why I say that is the solution is a friend of mine who had the same boat(Pilot 30) had a thruster installed. It was installed with 1 group 31...it's own batterycharger....AND NO OTHER WAY TO CHARGE IT WHILE AWAY FROM THE DOCK!!!! He seems to do just fine with multiple uses with no charging mechanism on it(other than at the dock). Granted, a Mainship Pilot 30 is a light boat with low windage. I personally would find a way to get some charging up there. BUT, the point here is the length of the wiring run. Maybe someone on here can do the math on how big the wires should be for that much voltage over that distance. But I am willing to bet....that is your problem...as you have already eliminated the thruster itself as well as the batteries(ie they aren't your problem). If I would have kept that boat, I would have rewired my thruster to have a battery right next to it!!!!
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Old 10-19-2013, 12:40 PM   #5
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I agree. . . when you're talking high amperage 12 volt systems, it's very important to keep cable runs very short and the larger the cabling the better.
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Old 10-19-2013, 01:03 PM   #6
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Hello All, I am running the thruster with the engine at idle while docking. The batteries were installed in april & boatyard said they were fine. They also said the wiring checked out ok to the thruster. I guess the run is 12ft or so. There is room to put a battery next to the unit. I do believe the alternator is going, as the yard said and the way my volt guage acts. I am installing a new alternator on Monday afternoon, so we will see if that corrects it, if not go to plan B and get a seperate battery up there. Thanks to you all for your input.
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Old 10-19-2013, 01:08 PM   #7
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Have no drop in thruster speed/power with my large capacity alternator running off the 80-h.p. engine. The 24-volt system can't hurt either.

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Old 10-19-2013, 03:09 PM   #8
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The power draw on an electric bow thruster is very high. A 12V unit can easily draw 350amps (175 for 24V unit). You need big batteries and short heavy gauge cables.
Our 24V thruster is fed by 2x4D batteries in series. You might need bigger batteries that 31's. I do not think you will get much help from an alternator, especially at idle.
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Old 10-19-2013, 03:20 PM   #9
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I do not think you will get much help from an alternator, especially at idle.
The idle on my JD (850-900 RPM) is over 35 percent of maximum engine speed (2400 RPM).
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Old 10-19-2013, 03:32 PM   #10
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Mark: So is mine (850 vs 2600rpm) but I still do not think the alternator puts out much at low (850) rpm. Have you measured the output? I have not done this but next time on the boat I will see if the Link2000 can read charging amps at idle from our 135amp alternator. What I do know is that at idle, we are right on the cusp of negative current on our Cummins engine ammeter.
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Old 10-19-2013, 03:53 PM   #11
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If the alternator could supply the thruster, we almost would not need a battery.

Normally a 80 amp or 150 amp alt helps very little with the thruster, as Chrisjs
Has said.

OP,
Old thruster dragged voltage down.
New thruster drags voltage down.
In my view thruster should run from the battery with engine off.
I'm going to guess now, once new alternator is installed, same issue will be there.

Not all yards/mechanics are created equal......
While 4' of cable would be better, it used to work fine with 12'. (I assume).

Your yard is missing something.
Dirty contacts on a solenoid
Bad connection. (I know they checked them, they may of missed one)
Bad cable crimp end unseen under shrink tubing (same as bad connection)
Bad battery, easy to load check, however it's not that easy.

Since you are paying for this work, the yard is guessing and billing you.
Find another yard.
Good troubleshooting mechanics are hard to find.

Hope this helps.
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Old 10-19-2013, 04:07 PM   #12
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I agree. Given adequate wiring, high-capacity batteries are essential. My thruster runs off the house batteries: dual 24 volt 200AH AGM batteries. One needs an alternator sufficient to keep them charged. It is no more than 10 feet between thruster and batteries.
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Old 10-19-2013, 05:26 PM   #13
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What gauge is the wire? It should be stamped on the casing. It should probably be 4/0.

If your voltage quickly drops to 10V then it's an electrical supply problem. Does the voltage stay down at 10V (or close to it) after to stop the thruster, or does it pop back up to 12.5V or so? If the voltage stays down then it's your batteries. If the voltage comes right back then I'd be looking at wiring, especially connections that are bad and heating up and getting worse while running the thruster. You may need to take voltage measurements along the cable route at each connection to find the bad one. Also check connections with a temp gun and look for temp rise. That migth actually be the best way to find a connection point that is heating up.

What does the thruster manufacturer say about battery size, cable size, and cable run length? I'd be surprised if they don't have guidelines. By gut says group 31 batteries are WAY too small. I'd think 4D or even 8D would be better, but checking the battery voltage after the drop to 10V will tell you a LOT.
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Old 10-19-2013, 05:47 PM   #14
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Thanks. I will check the wire size. The volt guage pops right back to 12.5v as soon as I release the thruster switch. I have the owners manual & will check their specs. for installation. My new 31 dc batteries are rated at 850 cca, stamped on top of the battery. Thank you all again!
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Old 10-19-2013, 09:14 PM   #15
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If the voltage is coming right back then I'd be looking really hard at all the connections. Use an IR thermometer if you can, measuring before and after a good run of the thruster. Connections can appear good, but be problematic, especially if old. Don't overlook the lugs on the ends of the cables. They are just crimped on and can corrode over time.

By the way, where are you measuring the 10V? Is that at the battery? The thruster? Somewhere else?
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Old 10-19-2013, 09:14 PM   #16
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Quote:
Originally Posted by Chrisjs View Post
Mark: So is mine (850 vs 2600rpm) but I still do not think the alternator puts out much at low (850) rpm. Have you measured the output? I have not done this but next time on the boat I will see if the Link2000 can read charging amps at idle from our 135amp alternator. What I do know is that at idle, we are right on the cusp of negative current on our Cummins engine ammeter.
I would like to know what you learn about the reading on the Link 2000. I have a similar reading at idle as you describe but no problem with thruster with two 8 D's and about a 20 ft. run of cable. Still, my old thruster is pretty tired. I would love to know what you replaced and what you have now. Did you need to do much tunnel work? Single or double props?
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Old 10-19-2013, 11:49 PM   #17
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I would think about two things - one bigger batteries and installing an Automatic Charging Relay from Blue Sea to keep the batteries full.
I would contact the support department of the thruster and ask what they recommend for batteries. Does your windlass run off the same batteries?
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Old 10-20-2013, 12:30 AM   #18
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I would like to know what you learn about the reading on the Link 2000. I have a similar reading at idle as you describe but no problem with thruster with two 8 D's and about a 20 ft. run of cable. ?
I'm wired exactly the same way with no problems.
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Old 10-20-2013, 02:42 AM   #19
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If you have a 20 foot run with a 3% voltage drop (there and back, I guessed the distance) you get this result:

Recommended Wire:
AWG 4/0
Capacity with derating factors: 378 amps.


The wire you select must be large enough to meet both ampacity and voltage drop requirements. These are the wire sizes this circuit needs to meet each requirement:

Ampacity (Add'l Derating Factors): Ampacity (ABYC Stds Only): Voltage Drop (ABYC): AWG 4/0 AWG 4/0. AWG 4/0

What size are you using now? As others have stated, this is your problem. I think you need to threaten your installer, maybe get him to put the old one back and rewire.
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Old 10-20-2013, 02:47 AM   #20
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By the way, you can find this stuff out for yourself on the Blue Seas site using their Circuit Wizard.

By the way, your thruster is not drawing CCA, it is drawing a load of 350 amps. CCA is a measure of the batteries capacity to do work and is some esoteric number like one volt drop per cell per some seconds at a certain temperature. That's not it but I'm giving you lot the opportunity to look it up as it's near my bedtime.

Never mind, here it is:

Cold Cranking Amperes (CCA)/Marine Craking Amperes (MCA)

CCA and MCA measure the power capacity of a battery. CCA is the discharge load in amps which a battery can sustain for 30 seconds at 0F/–18C without falling below 1.2 volts per cell (7.2V on 12V battery). MCA is similar, but is measured at 32F/0C and results in a higher number for the same battery.

The amount of current that a breaker or fuse can interrupt without malfunction is its Ampere Interrupt capacity (AIC). The required AIC for a circuit breaker or fuse is determined by the power capacity of the battery.

Here's more: if your battery has a capacity of 500 amps, that means that it can produce 500 amps in an hour. If you use your thruster for one minute, it has a load of 350 amps but it has only drawn down the battery by 350/60=5.8 amps. That mean a normal alternator will have no difficulty charging the battery back up but a normal alternator can't carry a 350 amp load. You should also use starting-type batteries for you thruster as they are designed for that large short-term load like a starter motor (a thruster motor probably is a starter motor) and the batteries will be topped up immediately by the alternator. House batteries don't like that as much.
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