Hello how safe or unsafe is it to mix batteries by manufacturer? I was thinking of buying SOKs, but I may want to build my own packs with Fortune cells too later, I haven't decide. I just heard it could be bad to mix cell makes/models. Is that only because of the health of cells?
Mixing Batteries? Manufacturers?
- Thread starter Devin82m
- Start date
It is not optimal. If you stay with the same chemistry and same performance characteristics, it is very common for people to mix both brands AND capacities.
Series components MUST have the same capacity, i.e., don't put a 100Ah battery in series with a 200Ah battery for 24V. You now have a big 100Ah battery that won't function well.
Signature link #2 "Wiring" contains "best practices" for optimal configuration of banks in general. They do not deal with different brands/capacities, but they are still "best practices" and minimize issues.
Series components MUST have the same capacity, i.e., don't put a 100Ah battery in series with a 200Ah battery for 24V. You now have a big 100Ah battery that won't function well.
Signature link #2 "Wiring" contains "best practices" for optimal configuration of banks in general. They do not deal with different brands/capacities, but they are still "best practices" and minimize issues.
I plan on keeping the chemistry the same and the capacity. I just bought Fortune cells for a 100 Ah pack, but if SOKs become available in reasonable numbers I could purchase some of them as well. Do you think that would cause an issue?
Someone in another post mentioned "eddy currents", is that common and what issues would that cause?
Eddy currents are small fluctuations between batteries due to shared loads. Even if they are sharing 50% of the load, it's not exact. They may be sharing 45-55% of the load at any given time (and different current levels), and there can be fluctuations in current as loads or charges change as the batteries don't respond slightly differently.
In a severely imbalanced bank, with wild disparities between component sizes, these can be common and likely severe enough to substantially exceed the operating limits of the smaller components.
Once you have a bank wired using "best practices" (as close as you can given that you're deliberately ignoring the "same capacity" best practice), use a clamp DC ammeter to confirm the current passing though each battery does not exceed its ratings for high charge and discharge scenarios.
OK, but the general answer is stay with the same brand and capacity? I mostly want to confirm it's a pretty hard yes or no. If it's pretty open then I want to confirm that. I will never put any packs that are overall lower or higher capacity together, but is minute differences between the packs (aka different brands using different brand cells) then I need to know that too.
My plan was Fortune Cells with SOK, both 100 Ah.
You may need to dumb down your answer for me.
OK, but the general answer is stay with the same brand and capacity? I mostly want to confirm it's a pretty hard yes or no. If it's pretty open then I want to confirm that. I will never put any packs that are overall lower or higher capacity together, but is minute differences between the packs (aka different brands using different brand cells) then I need to know that too.
My plan was Fortune Cells with SOK, both 100 Ah.
You may need to dumb down your answer for me.
If you ask a manufacturer or system designer or anyone that might have liability in the situation, they will say "same brand, same age, same capacity."
Lots of examples of folks running different brands, different ages and different capacities.
OK, so with that said, what does "same age" mean? Same year? Same month?
What does same capacity mean? What's the allowable variation?
I mean theoretically, based on that statement, I may not be able to go with the same brand. I mean I may buy more cells in 6+ months to make a 200 AH setup. Then maybe a year down the road I will buy more to expand it further.
A big question based on the eddy current issue, what damage is done if it is in the "bad" range? Are there methods to reduce or eliminate the issue if it occurs? Does having the same brand/model of BMS help? Like if I put the Overkill Solar BMS on the SOK?
Sorry for the questions, I need detail, facts, data.
Same rating, purchased at the same time, same brand. That's the recommendation.
There's what's recommended and then there's what's done. It's a choice. If you search the forum, you may find examples of where people have tested their bank to confirm operating currents are acceptable. I personally can't think of an example where I read there was a problem, but I haven't read the whole forum.
I have 8X (4S2P) T-1275 150Ah 12V Trojan FLA with TESTED capacities ranging from 75-95% of rated. They also range about 2 years apart in age. I pay attention to them and treat them as though they are all 75% even though one whole string is in really good shape. I also have active balancing on them. Their current flows were within about 10% running about 50A and were well within limits. I also limit charging of the entire bank based on the weakest battery to make sure that I'm not straining the weakest one.
Note the above is a worst case type of scenario. I have 4 batteries in a string that all have different capacity - never recommended. Ever. It works fine because I pay attention to it. If one of the strings was 150Ah and the other 100Ah, but all string components were well-matched, I wouldn't pay much attention at all.
If you find the batteries are out of limits, you reconfigure to try and shift current, or you split them up and come up with a plan B.
This is a DIY forum. If you need rigid rules, indisputable facts to justify all actions/decisions, you're probably going to be disappointed.
Consider that you're accepting the "same brand, same capacity, same age" as gospel because that's the recommendation. None of them have hard data to back it up, it just passes the logic test - they should perform the same. When you can take DISsimilar batteries and verify they are performing within limits, that's hard data.
Hopefully @SteveS will chime in because I have a faint recollection he said something about his results.
That helps, yeah like to see facts when people claim a negative. If a lot of people are getting away with different brands and capacities then that's one thing.
Buying multiple batteries at once is not much of an option for me right now, but one off here and there over this year, possibly. What I may do is buy another 100 Ah Fortune in the next month or two to make the mobile (hand truck) emergency system I want for some basic items in our house. I'll get a 4000 Watt inverter and we should be set without having to get out the generator. I will charge it using AC (Victron charger) and eventually get a charge controller that can handle one of my 5 320 Watt panels that are still sitting in my shipping container. I would go with one of those all in one systems Will pushes, but they only go up to 2000 watts for 12v and I prefer to keep my system simple at 12v. I want to be able to power at least one of our refrigerators, router, modem, LCD TV, and a few laptops.
We had a power outage Sunday and I ran our router and modem for over an hour on my little 10 Ah LiFePo4 pack I built a couple years ago using a little 300 watt car inverter, I have a feeling it could go much longer. I mean they were being powered by my 15 year old UPS for about 30 mins before it ran out (I'm going to be replacing that old warhorse).
Buying multiple batteries at once is not much of an option for me right now, but one off here and there over this year, possibly. What I may do is buy another 100 Ah Fortune in the next month or two to make the mobile (hand truck) emergency system I want for some basic items in our house. I'll get a 4000 Watt inverter and we should be set without having to get out the generator. I will charge it using AC (Victron charger) and eventually get a charge controller that can handle one of my 5 320 Watt panels that are still sitting in my shipping container. I would go with one of those all in one systems Will pushes, but they only go up to 2000 watts for 12v and I prefer to keep my system simple at 12v. I want to be able to power at least one of our refrigerators, router, modem, LCD TV, and a few laptops.
We had a power outage Sunday and I ran our router and modem for over an hour on my little 10 Ah LiFePo4 pack I built a couple years ago using a little 300 watt car inverter, I have a feeling it could go much longer. I mean they were being powered by my 15 year old UPS for about 30 mins before it ran out (I'm going to be replacing that old warhorse).
That's the reality of it. Folks can't afford the bank they want all at once. A couple months into it, and they realize the bank is too small, so that add to it.
Nice. A full size fridge typically takes 2-2.5kWh/day, and I'd allow for another 1kWh for the rest. that's about 300Ah, and you'll need at least 2-3 of those panels to ensure you stay on top of it.
Glad to hear you had an option. Is your router and/or modem 12V? Mine is. It's a combo wifi router and DSL mode,. I cut the end off the power brick and added connectors, so I could feed by the brick or direct from the 5th wheel 12V. Far less efficiency losses. I suspect the two together use about 30W, so I would expect you could get close to 4 hours outta that 10Ah.
Good to know.
I had that thought about the router and modem being 12v and making a power cord up for it to bypass the waste of the inverter, but haven't checked yet. They are either 12 or 6 v I suspect. We live in North ID in the woods, so our ISP has towers all around the area and we have a little dish pointing at the tower, the dish is powered by POE and the max for POE is 48v, but 12v is the norm for virtually every POE device. I'm an IT guy who works from home, so got to keep that stuff going. At least my ham radio gear is all standard 13.8v (12v). I have buck converters for the odds and ends too. It's good to know my little pack can last that long. I have a 26 Watt Power Film rollup I can hand in the window of my office to charge it too.
