Charging 3 battery banks with shore, engine, wind and solar

[gpeacock]

Wow!

Great responses everyone. Here is what I've distilled so far.

1. Bow thruster is required to keep the Admiral happy at the wheel. I am willing to spend the value of the boat over again to keep the Admiral happy.

2. LiFePO4 is too new for me. Southern Chile is not the place to be playing with new technology.

2. The batteries on the house bank need to be AGM because I don’t have an easy way to vent them, although I have considered Hydrocaps etc.. I also feel that AGM give me my best chance at jamming 100A to 200A into them from the Alternators. If I could get the same charge efficiency from FLA I would put that back into the mix.
3. Space is the constraint causing the separate banks. I have no way to add more batteries to the house bank. Forward is really the only other place I can add capacity. Id love to combine the front bank with house (that’s the way it is now) and like the idea of a solenoid disconnect when using the thruster. That gives me an extra 200AH on house which I agree is really needed. I am definitely leaning this way. I could also throw an AC charger on that bank to bring them to happy state when docked occasionally. Both ends are fused to the ampacity of the wire.
4. IMHO charging voltage drop on the wire to the forward bat bank seems like a nonissue with 1/0 wire at 50 feet return. Sure initially there will be a drop but as current falls off this becomes less of an issue. With an open wire eventually the batteries will equalize. Only issue is temperature differences… Not sure how to address this.
5. I think the solution for the starter bat is the echo charger from the freedom with a disconnect switch. I am willing to manage this when sitting on the hook for weeks in the sun.
Keep them coming! I think this thread has worked out well as a good summary for a bunch of different ideas flowing around the forum. At a minimum its helping me clear the fog.

[sailinglegend]

Originally Posted by gpeacock

...4. IMHO charging voltage drop on the wire to the forward bat bank seems like a nonissue with 1/0 wire at 50 feet return.,,,,

Check out the voltage drop charts and you will see at 200 amps charging they don't produce big enough cables to minimise the voltage drop to less than 3%. The boost stage is important when you will see close to 200 amps. This will take you up to maybe 85% charged and this is perhaps what you will achieve most of the time - so it IS very important. To balance the charging of fwd and aft banks have a bus bar midships where all the charging sources join - then the cable lengths will be equalized.

Originally Posted by gpeacock

....Only issue is temperature differences… Not sure how to address this.

This won't be an issue with AGMs as they don't heat up like FLA because their charge efficiency is so much lower....[/QUOTE]

[hellosailor]

The charts I'm reading say for 1/0 cable and a 100' round trip there will be a 3% voltage drop at just a 30 amp load.

So there will be voltage drop, but the only time it might be an issue is during charging of the forward battery, and then one has to ask how often for how long will the forward battery pull how many amps? And of course, as it charges, it will pull fewer amps, making the voltage drop lower as it charges. Minimizing the issue.

AFAIK there will never be a 200A load on the cables. Even if the winch and thruster are both in use, that's what the forward battery is there for, and it will bear the brunt of the load.

Non-issues.

OTOH, the Admiral needing a bow thruster? How often is she going to dock the boat solo? Versus how much the installation is going to cost? And that's pretty much a sunk cost, I don't think you'll see a penny of it back when you try to sell the boat.

[ebaugh]

Originally Posted by gpeacock

Wow!

Great responses everyone. Here is what I've distilled so far.

1. Bow thruster is required to keep the Admiral happy at the wheel. I am willing to spend the value of the boat over again to keep the Admiral happy.

2. LiFePO4 is too new for me. Southern Chile is not the place to be playing with new technology.

2. The batteries on the house bank need to be AGM because I don’t have an easy way to vent them, although I have considered Hydrocaps etc.. I also feel that AGM give me my best chance at jamming 100A to 200A into them from the Alternators. If I could get the same charge efficiency from FLA I would put that back into the mix.
3. Space is the constraint causing the separate banks. I have no way to add more batteries to the house bank. Forward is really the only other place I can add capacity. Id love to combine the front bank with house (that’s the way it is now) and like the idea of a solenoid disconnect when using the thruster. That gives me an extra 200AH on house which I agree is really needed. I am definitely leaning this way. I could also throw an AC charger on that bank to bring them to happy state when docked occasionally. Both ends are fused to the ampacity of the wire.
4. IMHO charging voltage drop on the wire to the forward bat bank seems like a nonissue with 1/0 wire at 50 feet return. Sure initially there will be a drop but as current falls off this becomes less of an issue. With an open wire eventually the batteries will equalize. Only issue is temperature differences… Not sure how to address this.
5. I think the solution for the starter bat is the echo charger from the freedom with a disconnect switch. I am willing to manage this when sitting on the hook for weeks in the sun.
Keep them coming! I think this thread has worked out well as a good summary for a bunch of different ideas flowing around the forum. At a minimum its helping me clear the fog.

1) Nobody argues with the admiral...!!!
2) Probably not. Grenada wasn't the best place to do LiFePO4...I did it there but it cost around 20-25% more with shipping and duties.
2.2) There is a fellow with more experience than me that hates AGM, maybe he can comment. I've used them without problem, but not in a deep cycle application. I have not found them better or worse, just cleaner, lower maintenance and 2-3x the cost. Can you get...have you considered gel as an alternative? Of the three, I like lead acid. You can spend a lot on venting for the price difference.
3) I figured space was an issue...it always is. I don't think you absolutely need a solenoid to disconnect when using the thruster. Unless the the forward bank is disconnected, it's going to get the majority of the load and I think it almost impossible to exceed the ampacity of the 1/0 cable. With only a 1-2 Volt differential and the resistance in length of the cable it's self limiting. I'd probably just use a manual battery switch for the odd occasion you need to separate them.
4)You will work the aft house bank harder than the forward. The forward part won't probably ever fully charge. If you size the solar system so you don't routinely need to charge with the alternators, I think it will work OK because the voltage drop becomes far less significant with a low rate constant charge each day. If you routinely charge with the alternators for short periods, or any high current source I foresee a bigger issue. There is no perfect answer without independent charging sources for each, but the cost and complexity is probably not worth the trade off a few batteries.
5) Do you have a generator? The Freedom won't charge without shore power or a generator.

Good Luck!

[DeepFrz]

Don't forget when you connect up your battery bank it is always better to connect the + off one end of the bank and the - off the other end of the bank. This helps to equalize the charge level of the individual batteries and makes for a longer lasting battery bank. It is difficult to do this if you start combining two banks that are separated by a long distance. The cost of the cable becomes prohibitive.

Before you make up your mind about AGM batteries, take a look at several articles Maine Sail has written. He has done a lot of work to test and evaluate batteries. He has specialized equipment and is very good at documenting and explaining what results he gets.

AGM Batteries - Making The Choice - SailboatOwners.com

[ebaugh]

That's a great post by MaineSail on AGMs...and that is who I was thinking of that did not like AGM. But he needs to update it from gel to lithium for his next battery since he decided to join the dark side....

[gpeacock]

Getting closer!
Its 50 ft round trip to the forward bank and I just checked today its 1AWG cable not 1/0. Still at that distance I see 2.6% at 40Amps.
For charging I thought voltage was key at the absorption and float because thats where voltage is held... at bulk, charging systems just throw what ever they can and the batteries decide what volatge to sit at (simplified I know but this is the gyst isnt it?)
Im going to try ebaugh's theory and not but in a disconnect to start. I can always use the switch till I put a solinoid in if it is a problem.
Can any one confirm the comment on the Freedom 15's echo charger. I assumed it worked the same way as an echo charger and would charge the start bank with any source above 13.? Just read through the manual and it doesnt say otherwise.
Off to read the good article from MainSail on AGMs.
Again main reason for AGM's is charge efficiency. With the 2 100A alternators I want to hit 80 to 90% charge as fast as possible. I know Gel's wont take that high rate of charge (what the boat came with) and I thought FLA's were also keen to be less than around 1/4 c (100A or 150A in my case depending on how I connect things). Having said that, if I end up with a 600AH battery bank I guess 150A output is the most I could expect in real world conditions from my alternators anyway.
Thanks everyone I think the murkey waters are much clearer for me.

[ebaugh]

The factory recommends wet cell Trojans not be charged faster than 13% of their 20 hour rate. So this is indeed an issue with 6 6V 225Ah cells making a 12V 675Ah bank, about 100A is the max recommended charge rate.

[Andina Marie]

Originally Posted by ebaugh

I think you are the person who originally designed the first automated battery combiner...so you are certainly qualified to answer this question.

Let's use this example, but make the house bank 1000Ah to emphasize my point. Assume the engine battery is fully charged and the house bank is down 20-30%. The sun starts shining and my solar controller is properly programmed for several hours of absorption charge since the charge rate is especially slow. And we soon see the proper 14.4V absorption for quite some length of time. Won't that potentially boil the engine start battery since it's already fully charged?

This is a very common mis-conception. A Combiner puts batteries in parallel. If they are in parallel they are both at the SAME VOLTAGE. How could the engine battery be overcharged without the house bank also being overcharged? To "boil the starting battery" you will need to hold the voltage significanlty over 14.2 but the regulated output from the charging source prevents this. Boiling starts around 14.2 to 14.4 but the Combiner cannot increase voltage so the starting battery can NEVER be at a higher voltage than the house battery.

When first combined, current is going to flow from the starting bank to the house bank and after a few seconds they are at the same voltage. The Combiner will cycle off if that voltage is below 13 volts untill the solar brings the house bank back up. During each cycle, typically about 1 amp-hour of charge is transferred. Once both are at the same voltage above 13 volts they will stay in parallel at which time they both follow the programmed charging routine of the source regulator.

[Cheechako]

Bow thruster on a 34? do you really need that complication?

[Andina Marie]

Originally Posted by hellosailor

"voltage drop is not a concern because"
that could give folks the misimpression that all the 3-stage chargers that are VOLTAGE POINT based, are wrong. Perhaps better to say that within certain limits, a certain amount of voltage drop is not a stopper. That would depend on the voltages and the drops and other issues, like whether you care about a battery possibly not seeing the last 10 or 20% charge because it was "only" one or two tenths of a volt low. Wouldn't it?

YES but consider the scenario.

Batteries are in parallel with a long cable. Worst case situation, consider the charging sorce is directly on battery A and battery B is at some distance.

So during the bulk charging battery A is increasing to the first threshhold, say 14.3 volts and battery B is at a lower voltage due to the drop in the cables.

Although that drop can be significant in the early stages due to heavy current, by the time battery A reaches the 14.3 threshhold, charging current is down to about 10% of the initial value so the voltage at B could be perhaps 13.9 volts depending on wire gauge and length.

At this stage the charger switches to the next stage and lowers the current. At the lower current, the drop between the batteries will be less so their voltages will be closer. By the time the charger reaches stage 3 the current is minimal and they are at the same voltage.

BOTTOM line is the resistance of the charging line resulted in the charger switching to the next state earlier than it would have, had there been no cable resistance. So it spends more time in this stage but eventually both end up in parallel at the maintenance level of say 13.6 volts. Since fully charged internal voltage is around 12.8, both are fully charged.

Charging time is extended only by a few minutes due to switching to the next charging stage a little earlier.

So put in 00 charging cables if you like, they won't do any harm but not worth the expense to save a few minutes on charging time.

[Andina Marie]

I had a bow thruster on our steel ketch but he bitched like hell when he had to get into cold water.

[gpeacock]

Originally Posted by Cheechako

Bow thruster on a 34? do you really need that complication?

Guess I need to update my profile. We've got a 44ft center cockpit now. Longish keel with a skeg hung rudder and 30k pounds. Sure doesn't spin like the Cal

[gpeacock]

Andina's thinking on voltage drop is my thinking as well. Am I wrong?

[ebaugh]

Originally Posted by Andina Marie

This is a very common mis-conception. A Combiner puts batteries in parallel. If they are in parallel they are both at the SAME VOLTAGE. How could the engine battery be overcharged without the house bank also being overcharged? To "boil the starting battery" you will need to hold the voltage significanlty over 14.2 but the regulated output from the charging source prevents this. Boiling starts around 14.2 to 14.4 but the Combiner cannot increase voltage so the starting battery can NEVER be at a higher voltage than the house battery.

When first combined, current is going to flow from the starting bank to the house bank and after a few seconds they are at the same voltage. The Combiner will cycle off if that voltage is below 13 volts untill the solar brings the house bank back up. During each cycle, typically about 1 amp-hour of charge is transferred. Once both are at the same voltage above 13 volts they will stay in parallel at which time they both follow the programmed charging routine of the source regulator.

Thanks for the explanation. I knew the voltage would be the same (or slightly less). If I still had a garage (now its only an engine room), I'd have to run tests and see what really happens with meters....

But using my example, and the rules you mentioned, consider this description. With new batteries, you will see something like 12.8V on the start battery and 12.7V on the house bank at sunrise. The sun shines and the voltage rises quickly on the house bank since its not very discharged. If the combiner kicks in at 13.5 and off at 13.0, it's still going to add charge to the already fully charged start battery, since the house bank is already at 13.5V. Probably won't cycle the combiner since that's close to float for a fully charged battery. But then rises to 14.4, at 10AM, where the absorption phase on the smart regulator kicks in. It's either time programmed or current programmed to cut off at a low rate charge (2-3% of C?, I'd have to look this figure up). But at the beginning of absorption, the house bank is at 90% charge, the start battery still at 100% or slightly higher. Either way, to fully charge the house bank, we need to put 100 Ah more back in at 14.4 volts and the start battery is along for the ride. And it's only a 70 Ah battery to begin with. Certainly the majority of the current is gonna go to the house bank, but not all of it. What does go to the start battery is still needed in the house which increases the problem evening things out.

It's all good for float, that's the same number.

I can see where this is not as much of an issue with two banks of matching capacity, but I can't see a fault in the scenario described above which will tend to over charge the start battery. If it happened 26 times a year, probably not too big of a deal, but if it happens every day at anchor for a cruiser, it seems like a bigger issue.

I think you are better off combining and leaving it that way normally. Or in the case of a start battery leaving it isolated. But you do have to dedicate a small alternator that way. Or for this example, consider an isolation diode dropping the voltage by .5V or so since the start battery never really discharges, it just needs a float voltage.