Parallel 12V DIY 130Ah CALB Battery Output

[PeterH]

I need some advice.

For the past year, I've had 4 batteries in my camper. I built the batteries from 130 Ah CALB cells I pulled from an EV I built several years ago. I have a 100 Ah or 120 Ah Overkill BMS in each battery. The batteries are connected to the buss bars with Anderson plugs to make connection easy. For the strictly DC system, that all worked just fine. With the exception of the BMS disconnecting when any of the cells reaching 3.6 V which takes the battery out of the mix... guess that's the problem with a common port BMS.

I chose the 100 Ah BMS thinking that eventually I'd add an inverter which would draw a max of 200 Amps at a nominal 12 VDC from the battery bank. In parallel, each battery should have no trouble providing 25% of that 200 Amp load. Well, 'eventually' is here and this winter's project is to upgrade my camper with a Victron Multiplus-II 2x 120v inverter. BUT at a recent Victron training event, I learned about ripple voltage/current caused by the inverter when cables are too long, or resistance is too great between the inverter and the battery bank. Now, it is all about reducing resistance between the batteries and the inverter, so those Anderson plugs have to go. Oh, and I also have a 150 Amp thermal breaker between each battery and the buss bar as overcurrent protection.

Without the Anderson plugs, I want to move to battery terminals installed on the side of each battery box. I've searched this forum for discussions describing how others have boxed their batteries. I went with simple plywood boxes that work just great to protect the batteries. I have the BMS attached to the side of the battery, within the minimally vented box.

1. I plan to add battery terminal posts to each box and use 0 AWG cables between each battery and the buss bars, to eliminate the Anderson plugs.

2. Which overcurrent device has less resistance? A 150 Amp fuse, or a 150 Amp thermal breaker? I could add the fuse to the inside of the box for a cleaner installation. Or keep the thermal breaker in the circuit, but outside of each box.

3. Anyone see a fatal flaw in my intentions for this modification?

Thanks in advance for your thoughts!

 

[DJSmiley]

Fuse is way better. There are plenty of reports about those thermal breakers. The majority of them adds resistance (Get hot, even at 50% of their rated current). Hot = voltage drop..
Also, vibrations might cause them to trip as well... which can be pretty common in a van.

I don't see why anyone would prefer a thermal breaker on these locations. For outlets and sockets? Yes, might be easy, just reset them, since there is a risk of a short on a device or similar. (But in my campervan I still use fuses: Cheaper and more reliable imho, and i'm not expecting to use failed equipment on crappy wire which requires me to frequently trip a fuse/breaker...)

In all other situations: If they trip, there is something seriously wrong. They should't trip. In the rare case it does, you're going to fix it, and replace the fuse. Just resetting isn't going to fix anything wrong.

If you do plan using thermal breakers: Go for decent stuff like Bluesea. But that comes at a price. Those cheap black-with-red things: Avoid at any costs. Plenty of people experiencing voltage drops with these (thus heat)

As for Andersons: I agree, any connector will add resistance. If you really want to keep it modular (thus require plugs), go for higher-rated plugs than you need.. I would consider going for the 350A version if your current is >150A, and not opt for the 175A (Bigger connectors = more contact surface / lower resistance). I won't run a connector near its max rating.
Also, make sure you're getting genuine Andersons. There are plenty of imitations available. Probably works fine if you're pushing 50A on a 175A-rated-clone, but things might be completely different when pushing 150A.

 

[PeterH]

Thanks for sharing your opinion! Sounds like I should switch to fuses and avoid the Anderson plugs for this portion of my system. Been thinking I'll need to wire directly (without the easy disconnect plug) to the bus bar. I'll go with the Victron bus bar because it has built in fuses and will be consistent with all my other Victron equipment. Honestly, haven't had any trouble with the thermal breakers, but knowing where they come from, never had complete trust in them. Basically, this will be complete rebuild of my solar/power system. Good thing I like this sort of work!

 

[S Davis]

I would just go with a fuse on your positive terminal of your battery.

 

[PeterH]

What fuse did you use? I've ordered a set of terminal posts, similar to what you appear to be using. I like the idea of an internal fuse to keep things less cluttered on the outside, just not sure how I'll include it.

 

[S Davis]

I used this holder from west marine, I am using a 200amp fuse for now.

Fuse block

 

[PeterH]

Thank you! Funny, I found that same solution on Amazon and ordered one yesterday. I have four batteries to update in this project, but I'm buying the various bits for only 1 battery. I'm a slow learner sometimes... in the past I'd just order all 4 and take a chance. Soon as I know I have a workable design, I'll order the remaining quantity.

I do think you found the right solution for this. It reduces the number of connections and takes up a lot less space!

 

[S Davis]

No problem, I have plenty of room for components but my system is going to be mobile and set up so if one goes bad or the BMS fails I can just swap it out. I wanted an onboard fuse to make it safer handling the battery packs.