What the Heck are We Doing Wrong?

[BusboyJim]

Eric, On your test diagram, you show the input in Amps from the 2 chargers. Note that the two together (46 and 14) add up to about 60A of charge. You are using a 6500 watt genny. 6500W / 110V = 59Amps. it is not possible to get 110 amps out of two 55 amp chargers when the max the genny can produce is 59A. It appears to me that you are getting the max out of the two chargers. I know I'm a little late with the comment here, but I hope you got your problem solved.
It would be great to hear how you solved the issue.
JD

[eric@psmnv]

FLA is the most forgiving of temps and ignorance. Sealed lead batteries are expensive and shorter lived than their flooded brothers. Li will reward you in cold temps, by shutting down, unless you keep them heated. Ignorance with them is rewarded with smoke. NiFe is awfully forgiving - but expensive.

I like NiFe and could see myself shelling out the money, except it has a really poor charge/discharge rate. From what I can see, it's hard to run high-amp stuff for short bursts, and even harder to charge the things on the 4 hours of sunlight I get. Currently, I'm thinking maybe LiFePo4.

[Mike90250]

If I'm going to build a whole new bank, I'll explore a different chemistry than FLA. I need something that can put up with the temperature swings and my overall ignorance.

FLA is the most forgiving of temps and ignorance. Sealed lead batteries are expensive and shorter lived than their flooded brothers. Li will reward you in cold temps, by shutting down, unless you keep them heated. Ignorance with them is rewarded with smoke. NiFe is awfully forgiving - but expensive.

[Mike90250]

But not much in terms of amp hours.Not enough to hold us for a full 24-hour period.

then you get larger batteries, like L-16 floor sweeper batteries. Another alternative is to move to a 24V bank. When you run out of amp hours and
need more, go to a higher voltage system. It will require the same amount of lead, but configured in a more efficient manner.

[eric@psmnv]

Based on your load I think going to a bigger Ah battery system would make sense. Start looking at higher Ah Trojan batteries. You can find them using lower voltages like a 2V and then put 6 of them wired in series instead of 4 parallel banks of 12V.

If I'm going to build a whole new bank, I'll explore a different chemistry than FLA. I need something that can put up with the temperature swings and my overall ignorance.

[SunEagle]

But not much in terms of amp hours.Not enough to hold us for a full 24-hour period.

Based on your load I think going to a bigger Ah battery system would make sense. Start looking at higher Ah Trojan batteries. You can find them using lower voltages like a 2V and then put 6 of them wired in series instead of 4 parallel banks of 12V.

[eric@psmnv]

Yes, but it's for eight 12V batteries, not 6V batteries. In your case when you connect two 6-volt batteries in series, you pretend that's one 12V battery. So for the purposes of parallel wiring, you're using four batteries

Except that I wouldn't do that in your case if I could help it. Parallel is OK in float service with full-time AC power and occasional battery backup, but has trouble in cycle service as you've found out. So ditching the parallel batteries and going to one string or at most two in parallel, will probably give you much better service life.

But not much in terms of amp hours.Not enough to hold us for a full 24-hour period.

[sdold]

Yes, but it's for eight 12V batteries, not 6V batteries. In your case when you connect two 6-volt batteries in series, you pretend that's one 12V battery. So for the purposes of parallel wiring, you're using four batteries

Except that I wouldn't do that in your case if I could help it. Parallel is OK in float service with full-time AC power and occasional battery backup, but has trouble in cycle service as you've found out. So ditching the parallel batteries and going to one string or at most two in parallel, will probably give you much better service life.

[eric@psmnv]

Sounds good, I think with that setup the bulk and absorb should take at least 6 hours, are you running the generator that long?

I'd use busses or their suggested wiring then, it's important to keep all of the parallel paths equal so that the batteries have a chance of sharing the current equally. The battery internal resistances are very low, so small resistances in the cables are significant.

Edit: It just occurred to me that your method might not ever allow an Equalization cycle, that might be one problem.

The suggested wiring is for a 4-battery bank. Did you happen to see a wiring diagram for an 8-battery bank?

[sdold]

Sounds good, I think with that setup the bulk and absorb should take at least 6 hours, are you running the generator that long?

The upper left battery's positive terminal is crowded with other connections and there isn't room for more, so the bottom charger is connected to an adjacent positive terminal.

I'd use busses or their suggested wiring then, it's important to keep all of the parallel paths equal so that the batteries have a chance of sharing the current equally. The battery internal resistances are very low, so small resistances in the cables are significant.

Edit: It just occurred to me that your method might not ever allow an Equalization cycle, that might be one problem.

[eric@psmnv]

I think two or more of these in parallel should be OK as long as your wiring is sufficient, the chargers are more current-sources during the bulk phase anyway. By the way there is something screwy with the bottom charger's Positive cable in your diagram, it should go the the same terminal as the top charger.

I talked with Iota. They said connecting 2 of them is fine. They won't fight or get confused. Their total output is added together and becomes the input to the bank. The upper left battery's positive terminal is crowded with other connections and there isn't room for more, so the bottom charger is connected to an adjacent positive terminal.

It does sound like you are under-charging. What version of the iota charger do you have, is it the straight DLS55 or the one with IQ4? If it's the non-IQ4 version there is an option board for $25 or so that will give it the ability to do Bulk, Absorb and float at the higher voltages needed for cycle service. If you don't have that option then it's stuck at 13.6V (normally used when connected to a constant source of AC power).

I don't have the IQ4 version, but I do have an RJ-11 "two-step voltage jack" in the unit that raises the voltage to 14.2. I leave it in there all the time. Iota says that's fine as long as the battery is okay with that voltage, The T-105 spec sheet says the batteries are okay with 14.82 volts for bulk charge on a 12V bank.

[sdold]

By the way in case you don't have Autocad, here's iota's Autocad file with their suggested 4-battery parallel scheme, click the thumbnail to view:

iota charger parallel config.jpg :

[sdold]

I think two or more of these in parallel should be OK as long as your wiring is sufficient, the chargers are more current-sources during the bulk phase anyway. By the way there is something screwy with the bottom charger's Positive cable in your diagram, it should go the the same terminal as the top charger.

It does sound like you are under-charging. What version of the iota charger do you have, is it the straight DLS55 or the one with IQ4? If it's the non-IQ4 version there is an option board for $25 or so that will give it the ability to do Bulk, Absorb and float at the higher voltages needed for cycle service. If you don't have that option then it's stuck at 13.6V (normally used when connected to a constant source of AC power).

[eric@psmnv]

Based on my calculations 6 225Ah batteries wired in a 2 x 3 system will give you (3 x 225Ah x 12V x 25% = 2025wh) where 2kWh should get you through the day with only a 25% discharge.

The cabin is drawing 179 watts on average (more during the day, less at night), which works out to 4.3 kWh per day. If my math is right, with 8 good batteries we would theoretically be able to meet our needs with a 40% DoD. We've never seen that happen, so we must not be getting the banks charged right (or the temperatures around here are playing hell with the efficiency, or both). With only 6 batteries in the bank, we'd need a 54% DoD.

Assuming we can get the bank fully charged, we should be able to make do for a while with 6 batteries, but I can never tell when the batteries are fully charged. The Trojan T-105 spec sheet does not list a C-Rate. I do know that the generator can pump in at least 50 amps through the chargers. Any idea how long I should run the genny to get a full charge?

Everybody is always warning about how under or over charging your batteries will damage them. I feel like I'm flying mostly in the dark. I've probably damaged my batteries without even know how I'm doing it.

[SunEagle]

Based on the findings shown in my drawing above, I'd say the upper right battery is definitely bad. It's voltage is low and it is not accepting amps. Can I replace just that battery or would we have to replace the whole bank?

You may be right about the chargers. As someone pointed out above, the bulk charge voltage for these batteries should be around 14.7 V, but they never go above 14.0 even when the generator is pumping amps into them through both chargers, so it seems likely that the bank is never being fully charged. I'm not sure what to do. We live off grid way up in the mountains and electricians don't come up here. Do you know any that do consulting by video?

It is best to replace the entire bank because a new one will drop quickly to the life of the older ones. But if you got the money then you can try that or just take 2 of the worst batteries out of the bank and go with just 6 for now. Based on what you stated for load usage 6 of those batteries should be enough.

Based on my calculations 6 225Ah batteries wired in a 2 x 3 system will give you (3 x 225Ah x 12V x 25% = 2025wh) where 2kWh should get you through the day with only a 25% discharge.