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Old 24-09-2014, 03:00   #1
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24 volt engine bank charging from 12 volts

Hello Cruisers,

I was sure this has been asked before, but I can't find the answer.

I have an engine battery bank of two 12V calcium starter batteries wired in series to provide the 24 volts needed for our Nissan diesel. The engine has its own 24 volt alternator, and the engine charging systems seem to be working well.

I also have a house bank, currently a pair of pretty buggered 12 volt deep cycle calcium batteries, and an equally stuffed 12 volt AGM. These are charged by a 420W MPPT solar regulator (Votronic) with 280 watts of solar panel, an Aerogen 6 (300 Watts) and a Hyundai 100 Amp alternator.

Simplistically I have assumed that should the engine bank go flat, I would pull the two 12 volt batteries from the house bank and use them in series to start the engine. And when I do finally replace the house bank, I was going to make sure that I had at least two 12 volt "cells" that I could cobble into 24 volts.

BUT, I just finished the complete boat rewire (and I do mean COMPLETE), sat back to admire my handiwork, and then firmly applied my palm to my forehead. One of the things I did in the rewire was move the house bank from the stern to a cabinet at midships. Much better weight distribution, shorter cable runs, better access, etc etc... but now if I want to apply my engine starting solution I have to pull the batteries out of the cabinet, lug them down to the stern and wire them in there. Previously the house bank sat directly below the engine bank and all I had to do was move the cables around. (I have at least left the old mounting shelves in place so I don't have to dismount the engine batteries to do this.)

OK, if I have to start the engines in a hurry, this is probably going to be the best solution, but I think I really should have a good way of charging the engine bank from the house bank if required.

Is this a good idea, and if so, given the ingredients listed so far, what would people suggest I add to the mix, given that I have a 12 volt source to charge a 24 volt destination? I could isolate the engine batteries from one another to charge them, but such a setup seems an invitation to an almighty bang if I forget to isolate them before I connect them up to the house bank to charge.

FWIW, I do have a spare Morningstar Prostar 12 solar reg which is 24 volt compatible, so I could feed solar into that, but again, that means switching things over (switching the panels from the MPPT to the Morningstar controller) which is another thing to forget. Ideally I would have some kind of automatic charge monitor that remained connected to the engine batteries, and used spare power from the house bank to keep the engine batteries charged up. Maybe something smart enough to let me know if it was needing to do a lot of power transfer thus indicating a problem in the engine power system before it became a serious issue.

Does such a thing exist, or is there a better way of doing this?

Matt
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Old 24-09-2014, 08:20   #2
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Re: 24 volt engine bank charging from 12 volts

Going to require some additional HD wire pulls, but a solution is at hand without moving the bats.
Lloyd

texasindustrialelectric.com




Quote:
Originally Posted by GILow View Post
Hello Cruisers,

I was sure this has been asked before, but I can't find the answer.

I have an engine battery bank of two 12V calcium starter batteries wired in series to provide the 24 volts needed for our Nissan diesel. The engine has its own 24 volt alternator, and the engine charging systems seem to be working well.

I also have a house bank, currently a pair of pretty buggered 12 volt deep cycle calcium batteries, and an equally stuffed 12 volt AGM. These are charged by a 420W MPPT solar regulator (Votronic) with 280 watts of solar panel, an Aerogen 6 (300 Watts) and a Hyundai 100 Amp alternator.

Simplistically I have assumed that should the engine bank go flat, I would pull the two 12 volt batteries from the house bank and use them in series to start the engine. And when I do finally replace the house bank, I was going to make sure that I had at least two 12 volt "cells" that I could cobble into 24 volts.

BUT, I just finished the complete boat rewire (and I do mean COMPLETE), sat back to admire my handiwork, and then firmly applied my palm to my forehead. One of the things I did in the rewire was move the house bank from the stern to a cabinet at midships. Much better weight distribution, shorter cable runs, better access, etc etc... but now if I want to apply my engine starting solution I have to pull the batteries out of the cabinet, lug them down to the stern and wire them in there. Previously the house bank sat directly below the engine bank and all I had to do was move the cables around. (I have at least left the old mounting shelves in place so I don't have to dismount the engine batteries to do this.)

OK, if I have to start the engines in a hurry, this is probably going to be the best solution, but I think I really should have a good way of charging the engine bank from the house bank if required.

Is this a good idea, and if so, given the ingredients listed so far, what would people suggest I add to the mix, given that I have a 12 volt source to charge a 24 volt destination? I could isolate the engine batteries from one another to charge them, but such a setup seems an invitation to an almighty bang if I forget to isolate them before I connect them up to the house bank to charge.

FWIW, I do have a spare Morningstar Prostar 12 solar reg which is 24 volt compatible, so I could feed solar into that, but again, that means switching things over (switching the panels from the MPPT to the Morningstar controller) which is another thing to forget. Ideally I would have some kind of automatic charge monitor that remained connected to the engine batteries, and used spare power from the house bank to keep the engine batteries charged up. Maybe something smart enough to let me know if it was needing to do a lot of power transfer thus indicating a problem in the engine power system before it became a serious issue.

Does such a thing exist, or is there a better way of doing this?

Matt
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Old 24-09-2014, 08:20   #3
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Re: 24 volt engine bank charging from 12 volts

If the 24v bank is only for starting the engine and has its own alternator and regulator you should never have a issue provided you run the engine periodically to keep them charged up. Keep them isolated and keep things simple. If anything add a meter with a low voltage alarm to monitor. While connected to a 110v source you can charge individual batteries in a series bank but it is kind of a odd setup as you need a charger with a sep pos and ground for each battery, promariner makes some small 10 amp potted ones that you can do this with but they are not programmable.


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Old 24-09-2014, 08:53   #4
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Re: 24 volt engine bank charging from 12 volts

I would pre-make up some battery starter cables. So the engine can be started with the house bank. With the correct terminals on the cables you should be to hot wire the system (and change the batteries to series) reasonably quickly if the start battery fails. I think this is important.

The cables will need to be thick, but 24v helps a lot.

You should not normally need to charge the start battery via solar, but you could once again rig up the correct cables before hand. I don't see this as very important.

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Old 24-09-2014, 09:44   #5
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Re: 24 volt engine bank charging from 12 volts

Quote:
Originally Posted by Cruisingscotts View Post
If the 24v bank is only for starting the engine and has its own alternator and regulator you should never have a issue provided you run the engine periodically to keep them charged up. Keep them isolated and keep things simple. If anything add a meter with a low voltage alarm to monitor. While connected to a 110v source you can charge individual batteries in a series bank but it is kind of a odd setup as you need a charger with a sep pos and ground for each battery, promariner makes some small 10 amp potted ones that you can do this with but they are not programmable.


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Yes, that.

There is almost no reason other than some defect in wiring, or battery allowed to go bad, or engine not run for many months, for your start batts to go down in a system set up like yours.

I would really not worry about it. In case of some freak accident, you can disconnect and lug the batteries from the house bank.

OR -- if you have time, of course -- you can charge the start bank, if you have a separate AC charger for it, from the house bank via the inverter.

In my opinion, it is a totally superior arrangement to have the engine start batt completely separated from everything else and charged by its own alternator. You have this, so I would reap the rewards and not worry about it.

I would also not bother with voltage alarms on that bank, personally.

My boat is set up like that too. It has a separate Newmar AC powered charger for the start bank, which I almost never use, and a separate voltage meter at the nav table, which I never look at. Start batteries in this kind of duty last for 10+ years, and you just don't need to think about them as long as you are not going for long periods without running the engine.
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Old 24-09-2014, 09:52   #6
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Re: 24 volt engine bank charging from 12 volts

Quote:
Originally Posted by noelex 77 View Post
I would pre-make up some battery starter cables. So the engine can be started with the house bank. With the correct terminals on the cables you should be to hot wire the system (and change the batteries to series) reasonably quickly if the start battery fails. I think this is important.

The cables will need to be thick, but 24v helps a lot.

You should not normally need to charge the start battery via solar, but you could once again rig up the correct cables before hand. I don't see this as very important.

KISS
I do keep jumper cables nearby my battery boxes, just in case. On my boat, the generator start batt is in the same box and is the same size and type as the main engine start batt, so it would be pretty simple to jump off in case of need.

But the OP is worrying because his house bank is now far away. I would, frankly, not worry about it -- how long does it take to pop out a couple of batts and put them into the engine start bank? I doubt if it would take much longer with his setup, than it takes me to get into my battery boxes, which are under the aft bunk with screwed-down lids.

I agree that solar charging is totally unnecessary unless the OP is planning to leave his boat for many months at a time without running the main engine. My main engine is run at least once a month, and at least once a week when I'm on board, so it's a non-issue for me.

By far the easiest way to "charge" the 24v start bank from a 12v house bank is to use an AC charger powered by the inverter, if there were every any real need for this. These items of equipment are both useful for other purposes, and many boats will already have them on board.

If one wanted to have a dedicated device for this, Sterling makes a 12v to 24v echo charger: http://www.sterling-power-usa.com/li...ct%20Sheet.pdf


But in my opinion, this is a big waste of money, since its only purpose is to do something you will likely never need to do.
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Old 24-09-2014, 14:38   #7
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Re: 24 volt engine bank charging from 12 volts

Well, I must say, this is very reassuring.

Some ideas to look into, including prewiring a "jumper lead" setup, which when I think about it would be easier than it first appears as the engine itself is in between the two battery banks so the cable run need not be all that long.

Loyd, I think I understand that solenoid/relay controlled system you have drawn but only just. I suspect it is quite clever so I will apply myself to it some more.

Thank you all for your advice,

Matt
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Old 25-09-2014, 03:37   #8
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Re: 24 volt engine bank charging from 12 volts

To ensure the 24V starter bank is always charged, then I would suggest a 12-24V battery charger/maintainer always on is the way to go ensure the starter batteries are always fully charged. That would also protect if the 24V alternator goes phut.
The other scenario is a battery failing, where you can either borrow one of the house bank or disconnect the cables from one house battery and use jumpleads. While you could use high power relays to do this, I would be cautious as over a long period they can go high resistance and cause problems in the normal configuration.
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Old 25-09-2014, 11:41   #9
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Re: 24 volt engine bank charging from 12 volts

Quote:
Originally Posted by GILow View Post
Hello Cruisers,

I was sure this has been asked before, but I can't find the answer.

I have an engine battery bank of two 12V calcium starter batteries wired in series to provide the 24 volts needed for our Nissan diesel. The engine has its own 24 volt alternator, and the engine charging systems seem to be working well.

I also have a house bank, currently a pair of pretty buggered 12 volt deep cycle calcium batteries, and an equally stuffed 12 volt AGM. These are charged by a 420W MPPT solar regulator (Votronic) with 280 watts of solar panel, an Aerogen 6 (300 Watts) and a Hyundai 100 Amp alternator.

Simplistically I have assumed that should the engine bank go flat, I would pull the two 12 volt batteries from the house bank and use them in series to start the engine. And when I do finally replace the house bank, I was going to make sure that I had at least two 12 volt "cells" that I could cobble into 24 volts.

BUT, I just finished the complete boat rewire (and I do mean COMPLETE), sat back to admire my handiwork, and then firmly applied my palm to my forehead. One of the things I did in the rewire was move the house bank from the stern to a cabinet at midships. Much better weight distribution, shorter cable runs, better access, etc etc... but now if I want to apply my engine starting solution I have to pull the batteries out of the cabinet, lug them down to the stern and wire them in there. Previously the house bank sat directly below the engine bank and all I had to do was move the cables around. (I have at least left the old mounting shelves in place so I don't have to dismount the engine batteries to do this.)

OK, if I have to start the engines in a hurry, this is probably going to be the best solution, but I think I really should have a good way of charging the engine bank from the house bank if required.

Is this a good idea, and if so, given the ingredients listed so far, what would people suggest I add to the mix, given that I have a 12 volt source to charge a 24 volt destination? I could isolate the engine batteries from one another to charge them, but such a setup seems an invitation to an almighty bang if I forget to isolate them before I connect them up to the house bank to charge.

FWIW, I do have a spare Morningstar Prostar 12 solar reg which is 24 volt compatible, so I could feed solar into that, but again, that means switching things over (switching the panels from the MPPT to the Morningstar controller) which is another thing to forget. Ideally I would have some kind of automatic charge monitor that remained connected to the engine batteries, and used spare power from the house bank to keep the engine batteries charged up. Maybe something smart enough to let me know if it was needing to do a lot of power transfer thus indicating a problem in the engine power system before it became a serious issue.

Does such a thing exist, or is there a better way of doing this?

Matt
Apparently you have a handle on it. How long a run would it be from your house batteries to you starter batteries. Would it be feasible to run or have on hand a large jumper set. And do the cobbling without hauling the batteries.
It sounds like you are only concerned with the what if situation.

Feel sure you would have thought about this po-boy solution.
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Old 02-10-2014, 18:24   #10
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Re: 24 volt engine bank charging from 12 volts

I have installed one of the 12-24 chargers from here

Yacht Thruster Components & Accessories - Bow and Stern Thrusters

it was on a bow thruster bank, which required charge and the boat only had a 12v alt. it only chargers the 24v if the 12v bank is charging. kind of like an acr. some 12-24 converters would probably just constantly drain the 12v bank.

but as mentioned above it's not really needed for your case.
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