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Old 04-09-2019, 03:57 PM   #1
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Question For DC Experts

I have a house bank of 12 glass mat batteries. I have two 8D start batteries. All are less than two years old.

I have a Blue Seas ACR. This senses a charge going to any battery from any source and automatically combines the banks for charging. Once that charging source stops (ACR recognizes as drop in battery charge) it stops combining.

I started noticing last season that my start batteries, (as seen at the helm voltage meters) would start off really healthy but on a long day's run (say 8-10 hours) it starts to drop below the 24 volts and into the red. It is happening again now on this Bahamas trip, with some long days again.

To ensure all systems are supported I crank the genset until the end of my run

So I decided to sit staring at the ACR and work through what could be happening here. I have ended up with this theory that I would like you bounce off you and then a question.

I run the genset in the evening and charge everything up. The ACR relays since it senses a charge source. Next morning I start the engines and off we go. Now there is a charging source from the alternators. So the ACR relays again. And not only keeps the starts charged but also the large house bank - which the 4K inverter is using to run a house which currently included a large domestic fridge freezer AND a chest freezer. I don't know the ampage of my alternators but my theory is that they can't manage that load and do the engine starts are getting drawn down.

Thoughts on that? Anything else.

The question: I am thinking of turning off this relay and starting the genset. Then seeing if both banks are being charged without the ACR, i.e directly by the genset. Then leaving it off allowing the altenators to manage only the start batteries. And using the genset daily as I already do to charge the house. Thoughts on this?
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Old 04-09-2019, 04:16 PM   #2
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If you are cruising with main engines and no gennie, and alts are being over run by load, they will get HOT trying to pick up the load. Go in ER and see how hot they are with engines on. If any are cold, sounds like a pooped alt or ACR is somehow not combining.

Redneck troubleshooting!

Can also put a voltmeter on alt output lugs and see what it reads, should be about 28V. If alt is cold and only reading 25 or less, it is not working.
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Old 04-09-2019, 04:23 PM   #3
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If you're going to check alternator temperatures (which is a good idea), a laser light temperature gun as opposed to your hand, is a much safer way to go.

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Old 04-09-2019, 04:23 PM   #4
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If you are cruising with main engines and no gennie, and alts are being over run by load, they will get HOT trying to pick up the load. Go in ER and see how hot they are with engines on. If any are cold, sounds like a pooped alt or ACR is somehow not combining.

Redneck troubleshooting!

Can also put a voltmeter on alt output lugs and see what it reads, should be about 28V. If alt is cold and only reading 25 or less, it is not working.
Will the alternators throw 24+ in idle?
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Old 04-09-2019, 04:26 PM   #5
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If you're going to check alternator temperatures (which is a good idea), a laser light temperature gun as opposed to your hand, is a much safer way to go.

Ted
I have a gun, and can see the alternators from one of the ER access doors. Just not sure if doing so at idle will tell me much.
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Old 04-09-2019, 04:33 PM   #6
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I have a house bank of 12 glass mat batteries. I have two 8D start batteries. All are less than two years old.

I have a Blue Seas ACR. This senses a charge going to any battery from any source and automatically combines the banks for charging. Once that charging source stops (ACR recognizes as drop in battery charge) it stops combining.

I started noticing last season that my start batteries, (as seen at the helm voltage meters) would start off really healthy but on a long day's run (say 8-10 hours) it starts to drop below the 24 volts and into the red. It is happening again now on this Bahamas trip, with some long days again.

To ensure all systems are supported I crank the genset until the end of my run

So I decided to sit staring at the ACR and work through what could be happening here. I have ended up with this theory that I would like you bounce off you and then a question.

I run the genset in the evening and charge everything up. The ACR relays since it senses a charge source. Next morning I start the engines and off we go. Now there is a charging source from the alternators. So the ACR relays again. And not only keeps the starts charged but also the large house bank - which the 4K inverter is using to run a house which currently included a large domestic fridge freezer AND a chest freezer. I don't know the ampage of my alternators but my theory is that they can't manage that load and do the engine starts are getting drawn down.

Thoughts on that? Anything else.

The question: I am thinking of turning off this relay and starting the genset. Then seeing if both banks are being charged without the ACR, i.e directly by the genset. Then leaving it off allowing the altenators to manage only the start batteries. And using the genset daily as I already do to charge the house. Thoughts on this?

Menzies, it might be helpful if you could draw us a picture -- also helpful to know which ACR you have...

https://www.bluesea.com/products/cat...harging_Relays

I think you are on the right track overall. Your alternator(s) output is not sufficient to run your house/inverter loads throughout a long day.

Do the voltage levels for your "house" battery bank track with what you are seeing for your engine batteries?

Re: "I have a house bank of 12 glass mat batteries. I have two 8D start batteries. "


Wow... the house bank is 12 batteries? What size are these? Again, a picture will help.

I am also wondering if your ACR is sized correctly for the load.

By the way, Blue Sea Systems has some of the smartest people on the planet. I have called them in on many projects (professional and personal) and they always blow me away...

re: "I am thinking of turning off this relay and starting the genset. Then seeing if both banks are being charged without the ACR, i.e directly by the genset. Then leaving it off allowing the altenators to manage only the start batteries. And using the genset daily as I already do to charge the house. Thoughts on this?"

Worth a try if it is easy to do, but I would really want to know more if it were me. By any chance, do you have a DC Clamp Ammeter? The AC ones are simple and cheap, but DC is another story. These things work on the same principle as your autopilot gyro-compass (magnetic fluxgate sensor), and they used to cost a fortune.

Now you can get one for around $100...and this one is bloody EXCELLENT.

https://www.amazon.com/gp/product/B00ICSW4QK

With the ability to measure up to 1000A DC, absolutely a lifesaver if you have trouble cranking. Don't leave port without one... ;-)
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Old 04-09-2019, 04:40 PM   #7
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I have a gun, and can see the alternators from one of the ER access doors. Just not sure if doing so at idle will tell me much.
Leave the transmissions in neutral and run the RPM up.

Ted
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Old 04-09-2019, 04:51 PM   #8
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This one.

https://www.bluesea.com/products/762..._-_24V_DC_500A

Batteries are 8AGC2, golf cart.

And yes, both banks track the same.

Wondering if the relay is designed to manage the pull from the alternator so keeping it from getting hot?
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Old 04-09-2019, 04:55 PM   #9
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I believe the ACR only joins the two banks together when the voltage goes above 27.2v for 30 seconds (https://www.bluesea.com/products/761...12_24V_DC_120A). It opens when the voltage drops below 25.5v for 30 seconds.

It seems like the alternator output is connected to the house bank and the draw on the house bank/alternator is causing the voltage to drop below the switching threshold of the ACR. While you are underway, the start battery is being drawn down by the electrical demands of the engine. With the ACR off, the inverter wouldn't affect your start batteries. I would start by mapping out your charging system. It sounds like you have two alternators providing charge. Are their charges combined to charge the house bank? A 4000 watt inverter at 24v would be drawing roughly 170 amps. It is unlikely the inverter is drawing that much current so a close examination of the charging system including the inverter/charger is needed, and that should start with a drawing.

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Old 04-09-2019, 05:02 PM   #10
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I would start by verifying that both alternators are outputting. Also seems like you may be missing a part somewhere. Two alternators on one start bank that latches to a house bank or vice/versa? Usually two alternators would employ an isolator which is not ideal since it will drop the alternator outputs down slightly but typical of most installations.

Easy enough to check the alternators by running the engines separately and watching what the voltage does. Also check the temperatures of all your batteries. You could have a bad one. Point and shoot IR will locate it or just run your hand across them and look for one or more with warm spots indicative of internal soft shorts. A failed/failing battery will cause mischief.

Could be more than one thing...
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Old 04-09-2019, 05:05 PM   #11
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Tom, I have a full set of wiring schematics from the build. I will have to see if the ACR is on there or a later addition.

You say the inverter wouldn't impact the starts if the ACR is off, but right now it is always on. That is my question, what would be the impact if I just turned it off.
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Old 04-09-2019, 05:07 PM   #12
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Singular or plural?

Quote:
Originally Posted by menzies View Post
This one.

https://www.bluesea.com/products/762..._-_24V_DC_500A

Batteries are 8AGC2, golf cart.

And yes, both banks track the same.

Wondering if the relay is designed to manage the pull from the alternator so keeping it from getting hot?

Above you said alternators, but now it's 'alternator' Is this a single engine setup?


If both battery banks are tracking the same, then it seems to me you are pulling more juice out of the batteries than your alternator(s) are putting back. What kind of RPMs are you turning on one of these long days?

Remember, an alternator rated at xxx amps is probably not putting out xxx amps until you get your RPM's up...


Does your inverter setup tell you how much juice it is pulling? Are you running monster loads (like the water heater) from your inverter throughout the day?
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Old 04-09-2019, 05:11 PM   #13
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One alternator? Is this a single engine setup?


If both battery banks are tracking the same, then it seems to me you are pulling more juice out of the batteries than your alternator(s) are putting back. What kind of RPMs are you turning on one of these long days?


Remember, an 80A alternator is probably not putting out 80A until you get your RPM's up...
Two engines, two Neville alternators. Running 1800.

I agree that there is more draw than they can handle, but how to turn off the house draw, and charge that with genset later.
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Old 04-09-2019, 05:15 PM   #14
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I would start by verifying that both alternators are outputting. Also seems like you may be missing a part somewhere. Two alternators on one start bank that latches to a house bank or vice/versa? Usually two alternators would employ an isolator which is not ideal since it will drop the alternator outputs down slightly but typical of most installations.

Easy enough to check the alternators by running the engines separately and watching what the voltage does. Also check the temperatures of all your batteries. You could have a bad one. Point and shoot IR will locate it or just run your hand across them and look for one or more with warm spots indicative of internal soft shorts. A failed/failing battery will cause mischief.

Could be more than one thing...
I am just about to turn off the ACR and start the genset to see if both banks are being charged. If not then I need to turn the ACR back on.

If they are being charged I will be able to see in the morning if the starts have retained the charge and only the house was drawn down. Then see if the alternators keep the starts green during my run tomorrow.

The "issue" with mapping everything out is that I am in the Islands Mon, and I am trying to get to a solution that works for now and solve it when I get back to home base!
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Old 04-09-2019, 05:28 PM   #15
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AHAH! (I think!)

I just went to turn the ACR off and found out that it is a three way rocker switch. On/Auto/Off!

It was set to On. I have now set it to Auto instead of Off, so will see what impact that has.

I'm now wondering if the yard, at the start of last season, when they were replacing all of the house batteries, needed to turn off the ACR to do their work and then just put it to On when they had finished.

Now I don't know exactly how this ACR works (but will make it a point to find out) and what the difference from On to Auto means, but it could be that the relay was always closed and relaying!
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Old 04-09-2019, 05:35 PM   #16
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Two engines, two Neville alternators. Running 1800.

I agree that there is more draw than they can handle, but how to turn off the house draw, and charge that with genset later.

Ideally you want to be able to run all day off the alternators. Not sure which Neville's you have, but the standard models are 35A units at 24V. By 1800 RPM you should be at 30A each (roughly). 60A at 24V is 1.44kVA which (by the time it gets through your inverter and I-squared-R losses), you probably have 1,100 watts to play with, both AC and DC. It's easy to use that up with a single A/C unit, or a slow-cooker or what-not. Nav electronics these days are surprisingly juice-thirsty.


Slip that DC clamp ammeter around your alternator outputs (each, individually), add them together. Then use the same technique to see what is going into the inverter and finally into your main 24v DC bus. This will tell you how much your alternators are actually putting out, and where it is going...


Good luck...
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Old 04-09-2019, 05:40 PM   #17
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Maybe I missed this, but are you combining a (presumably) 12V house bank with 24V starting batteries?
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Old 04-09-2019, 05:43 PM   #18
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Maybe I missed this, but are you combining a (presumably) 12V house bank with 24V starting batteries?
Nope both banks are 24v.

And to your point, I seem to be combined, but don't want to be!
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Old 04-09-2019, 05:51 PM   #19
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It sounds like you found your issue with the switch position. I was starting to wonder if it was one of the ML units with the switch installed, we had some similar issue a few years ago on one of our vessels here. IF that doesn't take care of it, I have an easy short-term solution for you that will get you back to civilization. Let us know.
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Old 04-09-2019, 06:13 PM   #20
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So I put it on Auto and started the genset. The house 24v is charging perfectly. The engine starts are not.

So clearly I have now separated the starts from the charging system, which probably means separated from the house draw as well, which is what I want.

I will watch the starts for another hour or so and if they definitely are not charging I will turn the ACR back to On to get those starts fully charged. Then once I turn off the genset I will turn the ACR to Auto again which will separate the starts from the house for the night. I can confirm that in the am.

Then tomorrow as we run I will monitor the starts to see that they are being maintained by the alternators. If so then I have my solution, and can turn the ACR to On in the event that I do need to charge the starts or need a parrallel start.

Will update on this tomorrow evening after our run from Georgetown to Long Island.
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