Battery Bank Limit?

[Ronnie]

Originally Posted by Framus

Appreciate all the feedback and opinions. If I still go through with Renogy, it'll be through Amazon to avoid that customer service nightmare for sure. But back to my initial question, is there any limit to how many batteries I can connect to my setup? If I had unlimited funds, is there any downside (besides space) to overdoing it with a battery bank and getting 4, 5, 6+ for a 400W solar setup?

There is a specific rate of charge range that is best for lead acid batteries, and by going to big they will not get charged properly. What works out is around half the batteries in amp hours as the amount of solar in watts. In other words 400 watts of solar and 200 amp of batteries. You can look it up online to get detailed charge rates and numbers.

[Framus]

Originally Posted by Ronnie

There is a specific rate of charge range that is best for lead acid batteries, and by going to big they will not get charged properly. What works out is around half the batteries in amp hours as the amount of solar in watts. In other words 400 watts of solar and 200 amp of batteries. You can look it up online to get detailed charge rates and numbers.

I'm definitely going with the li-ion batteries by Battle Born. So in that case?

[TheHubbardBus]

Originally Posted by BeNimble

If you go lead acid batteries, they do best when fully charged, so if you go too big, they might not get fully charged often. For lithium, they prefer to NOT be fully charged, so you can go as bigger is better.

You're absolutely right regarding the state of charge (SOC) most capacity-sparing for each chemistry during periods of non-use (storage). But in use, I believe most people's usage patterns would indicate doing the opposite of what you suggest.

Buying more battery than you need in lithium is wasting a lot of money, while negating their most noteworthy advantages: the ability to discharge deeply w/o incurring significant capacity loss, and a high cycle life. An unnecessarily-large lithium bank will sit at a higher SOC for longer periods in use, which is exactly what we don't want.

Deep cycle lead acid, on the other hand, likes sitting at a high SOC, so having excess capacity means that in use, they're sitting at higher SOCs for longer timeframes, & that's muy bueno. Also, LA is much more detrimentally impacted by increasing depth of discharge, so the more capacity you have, the shallower your discharge cycles, and the happier your batteries. And of course, LA capacity compared to lithium is much less expensive.

When not in use, keeping each chemistry in their happy range is easy. With LA, just keep the bank on a trickle charger so it states near 100% SOC all the time. With lithium, just draw it down to 40-60% or so w/o charging before cutting the draws.

Here's a resource to better illustrate the bit about lithium bank sizing (covered in the first few paragraphs). The entire site is Gold, though. Tons of info regarding lithium / solar.

Assembling a Lithium Iron Phosphate Marine House Bank | Nordkyn Design

[Ronnie]

Originally Posted by Framus

I'm definitely going with the li-ion batteries by Battle Born. So in that case?

I am not sure, I would ask the Battle Born

[BeNimble]

Lithium lasts longest when it is never recharged. If you have a giant bank, it will never get fully charged from a small solar panel. If you fully charge it you would be making a mistake, one that people used to lead acid make all the time. Should only charging it to 80% for maximum life, and with a big bank, you would never need to charge over 80%. Wasting money? Maybe.

Let me add, sure if you have full lead acid and only take out as much as your solar provides it stays full and all is good. But then you run the microwave too much, now what? you can't get it back to full from solar. Not a problem with the big lithium bank. It can stay half full no problem.

[TheHubbardBus]

Originally Posted by BeNimble

Lithium lasts longest when it is never recharged. If you have a giant bank, it will never get fully charged from a small solar panel. If you fully charge it you would be making a mistake, one that people used to lead acid make all the time. Should only charging it to 80% for maximum life, and with a big bank, you would never need to charge over 80%. Wasting money? Maybe.

No maybe about it. And you're wasting it for nothing.
80% SOC full to 80% DoD empty is 60% of capacity.
That's only 10% more than you'd get from deep cycle lead acid limited to 50% DoD.
You're paying lithium prices for lead acid performance.

What other lithium advantages are you throwing out the window?


Fast charging. Lithium can charge at C/1 or more. LA a fraction of that.
But you propose under-sizing your charging source relative to capacity.

High discharge current. But you propose a large bank where each battery trickles current.

So once again you've turned your lithium bank into the LA equivalent.

Will you maximize cycle life? Sure. But lithium has a finite lifespan regardless of cycles. Going to extreme lengths to maximize the already extremely high cycle life inherent to lithium chemistry will only result in aged-out batteries with cycles never realized. Money wasted - definitely.

And what happens when something goes wrong, and that unnecessarily large bank goes tits up. That's potentially a lot of cheese all up in smoke.

Charging to a high SOC is not what harms lithium chemistry. Leaving it there is. There are two ways to avoid that happening. Your way, where you neuter everything positive about lithium, or the way I linked to, where you size the bank appropriately so it's actually being used, not just sitting there burning a hole in your wallet.

Originally Posted by BeNimble

Let me add, sure if you have full lead acid and only take out as much as your solar provides it stays full and all is good. But then you run the microwave too much, now what? you can't get it back to full from solar. Not a problem with the big lithium bank. It can stay half full no problem.

Alternatively, you could size your panel array appropriately, so that it's able to maintain the necessary SOC to power your anticipated loads, to include your microwave ;) There's no law saying you can only buy one panel.

[rffffffff]

Originally Posted by Shorty Wandermeyer

Thanks for the input and quick replies! The rationale behind keeping certain things on 12v makes good sense. In my scenario I'd probably keep my fridge, A/C, electric tankless water heater, and GFCI outlets on AC power and put lights, water pump, fans and USB charging stations on 12v. Does that make sense? Sounds like I need a converter now.
Do you happen to have a good wiring diagram for a set-up like the one we're talking about? I'm a better plumber than electrician

This is my diagram that I drew for someone else. It may help clear some of it up.

[Doktari]

I agree, bigger lithium is better. I connected my 200ah Lithium to my alternator as well as solar and now I need to double my Lithium to 400ah because it charges so quickly and I want to use the middle capacity. I like 200ah. I’m going to really like 400ah.
To address the OP’s question: I could add 600ah or 800ah if I wanted and it would only make it better. Just remember to protect your cables with properly sized fuse or breakers. That many batteries in parallel can deliver massive amount of amperage. Some people put a breaker or fuse on each lithium battery. It’s important to have well matched and balanced batteries which I would think you would get from Battleborn Batteries.

[TheHubbardBus]

Originally Posted by Doktari

I agree, bigger lithium is better. I connected my 200ah Lithium to my alternator as well as solar and now I need to double my Lithium to 400ah because it charges so quickly and I want to use the middle capacity. I like 200ah. I’m going to really like 400ah.

I don't understand why your solution to overly-rapid charging, or exceeding whatever SOC limit you choose, is to add more batteries? Do you limit your drive time based on how much charge your batteries require?

Why not just use a smart BtB charger that will limit alternator charge current and/or stop charging when you reach your chosen threshold? Why not do the same w/ your solar charge controllers? Both are far less expensive than doubling lithium capacity.

Not trying to come off argumentative. I know y'all are sharp cookies. I just don't understand this reasoning. There are obvious benefits to having more capacity, especially now that you've added another charge source to take advantage of. But that's a separate concern from the issue of maintaining a desired SOC.

[Doktari]

Sorry about the confusing posts. I think depression is affecting my brain. Thank goodness 2020 is almost over.
My B2B Charger is already turned down to 20 amps. I would like to be able to run it at 40 amps. And I am constantly watching my small battery so I don’t overdischarge. It would be nice to have a bigger battery and not worry about it as much. I could run loads in the longevity zone of 12.00-13.3 volts for longer with a bigger battery. The LifePO4 batteries would have a longer life because most of my charging is done by solar and a bigger battery would halve the charge rate.
It will be a tight fit but they will fit. I’ll just need to remove half of them to work on my engine.
And as I have not found a good BMS (battery management system) for my system a bigger battery is safer when not using a bms. Staying in the middle voltage of the pack and having low charge rates helps the cells stay equal.
Electrodacus is a excellent BMS but not for my components. I’m considering selling my charge controller and solar panel and following the instructions of Electrodacus. I’m going to try and hack the power switch in my inverter to work with the Electrodacus.
The internal BMS that comes with Battleborn batteries is even worse IMHO. As far as I know there are no wires for it to turn off a charger or inverter. The internal BMS simply disconnects the battery power. So it could potentially dusconnect under load and damage them. I sure hope there is more standardization of BMS systems soon.

[TheHubbardBus]

Thanks for the explanation Doktari. Well understood.

Have you worked with / considered the Orion Jr BMS?
Best thing about Battleborn is their warranty, assuming they honor it. Not to insinuate they wouldn't. But a 10-year warranty assumed they're around in 10 years. Still, they made it through 2020, so that's saying something.

[Doktari]

I looked at Orion jr bms a couple years ago but when I added up the cost it was around $600-$800. But that’s a lot less than some of them such as Batrium. Then I got interested in Energus BMS which looks like another quality BMS for around $300 with accessories. Then I went back to looking at Electrodacus which is even more affordable and quality. Around $200 with accessories like the DSSR20 charge controller. So I bought one but need to order the DSSR20 charge controller (only $37). But I’m struggling to figure out how it, or any of them, will disconnect the PV to my Morningstar Prostar Mppt charge controller. I thought I could simply use a DSSR20 as a PV disconnect but they are limited to 51 volts input. The input voltage of the Prostar is is around 80 Volts with the huge solar panel I’m using. I’m thinking of using the big panel and Prostar just for charging a ebike and replacing it with some smaller 12 volt panels and Electrodacus DSSR20 controller for the bus energy system. I new Lithium would involve some challenges but didn’t think it would take this long.

[TheHubbardBus]

@Doktari,


That's what I liked about the Orion Jr... it was generic enough so you could do your own thing w/ everything outboard of the unit itself, and powerful enough to do more than I ever wanted. But that comes at the cost of a steep learning curve (at least for me), and definitely a price tag. It was, in fact, the price & complexity of the BMS functionality I desired that has caused me to once again reconsider previously-discarded options.

That in itself may be a good argument for a 'large' lithium bank... A good BMS & the required hardware on a small bank has a significant impact on the cost / ah.

[JeffCurry]

Nate Yarbrough has a blog and newsletter signup, I’m attaching a link for his very intuitive and easy to read solar diagrams. A plethora of knowledge on solar, batteries and incorporating into many different setups.

https://www.explorist.life/solarwiringdiagrams/

[mymincave]

Originally Posted by Framus

I'm currently in the middle of a build and purchasing the 400w solar kit from Renogy. They make no mention of how many batteries they suggest and from researching the issue, there's no answer. Sorry for possibly being a complete noob here but is there any limit to how many batteries I can connect to my setup?

Will Prowse on YouTube has incredibly clear minded vids on every aspect of solar. His book “Mobile Solar Power Made Easy” has saved my sanity!

[Doktari]

If going the spendy but viable Victron Energy route I recommend reading the Victron books. I like them because they are very thorough and methodical in explanation. They are Energy Unlimited and Wiring Unlimited. They even sent me a hard copy free of charge but is available as a PDF download. They explain it in terms of a boat energy system but if it’s good enough for a boat it’s more than good enough for a bus. This is for people who want to grasp the fundamentals:
https://www.victronenergy.com/upload...limited-EN.pdf

[rffffffff]

Originally Posted by Doktari

I looked at Orion jr bms a couple years ago but when I added up the cost it was around $600-$800. But that’s a lot less than some of them such as Batrium. Then I got interested in Energus BMS which looks like another quality BMS for around $300 with accessories. Then I went back to looking at Electrodacus which is even more affordable and quality. Around $200 with accessories like the DSSR20 charge controller. So I bought one but need to order the DSSR20 charge controller (only $37). But I’m struggling to figure out how it, or any of them, will disconnect the PV to my Morningstar Prostar Mppt charge controller. I thought I could simply use a DSSR20 as a PV disconnect but they are limited to 51 volts input. The input voltage of the Prostar is is around 80 Volts with the huge solar panel I’m using. I’m thinking of using the big panel and Prostar just for charging a ebike and replacing it with some smaller 12 volt panels and Electrodacus DSSR20 controller for the bus energy system. I new Lithium would involve some challenges but didn’t think it would take this long.

Entering the conversation late and I haven’t read much of it but if you need to disconnect the panels from the charge controller in the event of a bms shutdown just use a contactor or relay with the coil powered by battery voltage. If the battery voltage goes away it’ll cut the panel to charge controller connection too. Been thinking of doing the same here.

[Doktari]

Originally Posted by rffffffff

Entering the conversation late and I haven’t read much of it but if you need to disconnect the panels from the charge controller in the event of a bms shutdown just use a contactor or relay with the coil powered by battery voltage. If the battery voltage goes away it’ll cut the panel to charge controller connection too. Been thinking of doing the same here.

Exactly what I decided to try. I ordered 3 SSR’s (solid state relays) and heat sinks today. I already had ordered one SSR after watching a video by Will Prowse recommending the Opto22 SSR (solid state relay) because they are made in USA and have lower failure rate. However the other 3 I ordered are made in China to try and save money. I hope I don’t regret it. Dacien at Electrodacus recommended getting the heat sinks to keep them cooler. I got a higher amp model, 40 amp, because I realized they would not get as hot. I’m using my system without bms currently. I check the cell voltages every few days. I was checking them several times a day when I started. I hope I don’t trash these batteries

[jeffmakley]

Renogy recommends at least a 12V 200ah on their 400W premium kit.

[rffffffff]

interesting to use an ssr. I am likely to go with something like this because it can handle some stupid high 900V and 500A I think, and in my experience they very rarely fail, although I never used tdk specifically. Something to consider if the ssr's become an issue with heat.

https://www.mouser.com/ProductDetail...uK%252BQ%3D%3D

Originally Posted by Doktari

Exactly what I decided to try. I ordered 3 SSR’s (solid state relays) and heat sinks today. I already had ordered one SSR after watching a video by Will Prowse recommending the Opto22 SSR (solid state relay) because they are made in USA and have lower failure rate. However the other 3 I ordered are made in China to try and save money. I hope I don’t regret it. Dacien at Electrodacus recommended getting the heat sinks to keep them cooler. I got a higher amp model, 40 amp, because I realized they would not get as hot. I’m using my system without bms currently. I check the cell voltages every few days. I was checking them several times a day when I started. I hope I don’t trash these batteries