High amp 12v box

[Infinityedge]

So I need to build a battery box to run a 12v winch.

The winch manual puts max amp draw at 430A.

I’m using headway cells from batteryhookup super beast pack converted to 12v. I’ve previously made a motorcycle battery out of these headway cells and was impressed with amp output and ease of build.

I have two 300A BMSs to run two 12v packs in parallel and give a bit of headroom for amp draw. Plan on mounting it in a dewalt tstak box along with a 30A solar controller and maybe a 120VAC->24VDC power supply if it fits. For outputs, battey lugs for the winch, a couple lower amp 12v outputs, and USB out & solar in because PGE sucks enough to need every solar generator I can get.

Now to the questions:

Fusing? Should I fuse the main feed or let the BMS handle it? Fuse on each bank or a single one for the output? Fused at 600A (or 2x 300A) or higher than the BMS rating? Should I individually fuse all the 12v outputs? How about the solar input to the charge controller?

Thermal? Given that this will primarily be used in the dirt and dust, it would be nice to keep everything sealed. I can open the top when 120VAC charging, but would rather it be as tight as possible for solar charging and high amp use. Should I just roll with it and monitor temps to see if I should change things? Glue in a big heat sink? Switch to a metal box? Add computer fans with filters?

Any comments or suggestions welcomed.

 

[HRTKD]

Never let the BMS be your first line of defense. Put a fuse in there.

One fuse or one on each battery? Forum members are doing it both ways. Best is to fuse each battery. But, if one fuse blows, the other won't be far behind because it had to pick up the full load.

Are these good quality BMS? Or cheap Chinese BMS that shouldn't be used for more than half their rating, continuously?

Why are you going to use a 120 Vac -> 24 Vdc power supply on a 12 volt system?

A winch isn't often used for long periods. You may find that the battery/BMS doesn't heat up enough to warrant active cooling.

 

[Infinityedge]

Never let the BMS be your first line of defense. Put a fuse in there.

One fuse or one on each battery? Forum members are doing it both ways. Best is to fuse each battery. But, if one fuse blows, the other won't be far behind because it had to pick up the full load.

Are these good quality BMS? Or cheap Chinese BMS that shouldn't be used for more than half their rating, continuously?

Why are you going to use a 120 Vac -> 24 Vdc power supply on a 12 volt system?

A winch isn't often used for long periods. You may find that the battery/BMS doesn't heat up enough to warrant active cooling.

Aren't all BMSs cheap Chinese BMSs? Regardless, my use case could probably be done with a 5500lb class winch, but those pull 300A at 5000 load while the 12000lb class winch I got is around 200A at the 5000lb pull. It should be rare to max out the winch. Plus I was citing max amp draw from someone on a jeep forum who was talking about max draw if everything was bound up. Looking at the manual now, they cite 350A for 12,000lb load. The bus bars are rated for 300A, which is one of main reasons I went with 300A BMSs rather than 200A and pushing closer to using all the BMS is rated for. I should have more than enough headroom for even a Chinese BMS.

The 120VAC->24VDC is so it can be fed into the solar controller which claims to use a charging profile optimized for LiFePO4 batteries. If I'm going to put in a solar controller so I can actually use panels during blackouts, I figured I might as well filter mains power input through it too.

Good point about cooling. The motorcycle battery I made is fully sealed and works fine because you don't crank for that long. The duty cycle for a winch isn't going to be that much as setup and teardown will take way longer than the pull. I think I'll start with a temp sensor then decide on fans after use.

Any thoughts on using a pair of 300A circuit breakers rather than fuses?

Thanks for the feedback. I'm looking forward to this project even if I was kinda forced into it given the amp ratings of off the shelf LiFePO4 12V batteries.

 

[MisterSandals]

my use case could probably be done with a 5500lb class winch, but those pull 300A at 5000 load while the 12000lb class winch I got is around 200A at the 5000lb pull.

How often and for how long would one use a winch?

 

[Infinityedge]

How often and for how long would one use a winch?

I live on a steep hill and have stuff too heavy to carry, downhill of where it should be. Even with dragging friction, most loads will likely be under 3000lbs. Full extension is 65’ with line speed ranging from 11.2 fpm to 5.8 fpm based on load (3000lbs vs 12000lbs). So worst case scenario of 11min at 350A, in reality, less than 6min at 160A. Setup and tear down will likely each take longer than the pull. Will probably do less than 10 pulls a day.

 

[MisterSandals]

Wow, thats some serious winching. Glad i asked before making a silly suggestion.

Just messing with numbers...
65' / 8 fpm = 8 min x 10 pulls = 80 min. (1.3hrs)

1.3h x 300A = 400Ah

 

[Infinityedge]

Wow, thats some serious winching. Glad i asked before making a silly suggestion.

Just messing with numbers...
65' / 8 fpm = 8 min x 10 pulls = 80 min. (1.3hrs)

1.3h x 300A = 400Ah

The pack is only going to be 96Ah, so recharging would be needed for that many pulls. Dragging the battery to the mains won’t be that big of a deal, but getting an extension cord that can handle that load to where it needs to be is. But most pulls won’t be 65’ or that up there in weight. And 10 pulls a day makes me hurt thinking about it. I’m just trying to bracket things with worst case scenario limits.

 

[HRTKD]

Aren't all BMSs cheap Chinese BMSs?

Nope. The 120 amp JBD BMS that I bought through Overkill Solar has been tested to run continuously at 120 amps.

For high amp situations, my preference is fuses, not circuit breakers.

I had two winch power setups. My front, permanently mounted winch was connected to the vehicle's AGM battery. The rear winch was in a cradle mount and I ran it two different ways. The first was from a Warn kit that connected the truck's battery to a plug at the rear bumper. That worked fine. The second was just a standard lead acid car battery connected to the winch. That worked OK, but I had to be very selective with how long I ran it.

I think your limitation is going to be how well the BMS hold up to the surge and continuous amp load.

 

[MisterSandals]

pack is only going to be 96Ah, so recharging would be needed for that many pulls.

So you will be recharging at least 3 times during the day. Maybe more if discharging at 3C.
How long do you expect it to take for each recharge?

 

[Infinityedge]

So you will be recharging at least 3 times during the day. Maybe more if discharging at 3C.
How long do you expect it to take for each recharge?

It's going to take over 3hr to fully recharge the battery. I seriously doubt I'd do more than two battery drains per day.

 

[Infinityedge]

Nope. The 120 amp JBD BMS that I bought through Overkill Solar has been tested to run continuously at 120 amps.

Still a "cheap Chinese BMS" though. On the plus side, it is hard to screw up shoving a bunch of mosfets on circuit boards too badly. I do try to inspect all solder joints prior to use. I don't have an inverter or heat load that could run 300A continuous to test it myself, but the number of mosfets and wiring cross section check out.

For high amp situations, my preference is fuses, not circuit breakers.

Not arguing, but is there a reason why?

Should the fuses be sized for the continuous current rating of the BMS or the surge current?

I had two winch power setups. My front, permanently mounted winch was connected to the vehicle's AGM battery. The rear winch was in a cradle mount and I ran it two different ways. The first was from a Warn kit that connected the truck's battery to a plug at the rear bumper. That worked fine. The second was just a standard lead acid car battery connected to the winch. That worked OK, but I had to be very selective with how long I ran it.

I think your limitation is going to be how well the BMS hold up to the surge and continuous amp load.

Yeah, I'm pretty sure the BMS will be the weak point, but I cringe at direct discharge, even of headway cells. The BMS claims 300A continuous 900A surge, but I'm not sure I want to be around an 1800A surge load.

 

[MisterSandals]

Yeah, I'm pretty sure the BMS will be the weak point, but I cringe at direct discharge, even of headway cells.

This was going to be my suggestion if your winching was for rare occasions of getting stuck or helping other stuck vehicles.

If you will be in close proximity to the winch and battery, you could get a battery monitor with alarms to let you know if any cells get low. In this case YOU would be the BMS and be responsible to shut down on alarm.
A little Battgo monitor with audible alarm is about $35.

 

[HRTKD]

Not arguing, but is there a reason why?

Should the fuses be sized for the continuous current rating of the BMS or the surge current?

Check out this thread.

Do DC breakers work?

I'm considering this kind of 200A breaker between 200Ah lifepo battery and 3000VA Victron inverter/charger.: https://www.amazon.com/YOUNG-MARINE-Circuit-Trolling-Mount-60A/dp/B076P8PS3Y What I have researched, these don't work properly and may even be dangerous. So what do you think? Or are...

diysolarforum.com

Fuse for continuous. 1.25 times the continuous amps.

 

[Infinityedge]

Check out this thread.

Do DC breakers work?

I'm considering this kind of 200A breaker between 200Ah lifepo battery and 3000VA Victron inverter/charger.: https://www.amazon.com/YOUNG-MARINE-Circuit-Trolling-Mount-60A/dp/B076P8PS3Y What I have researched, these don't work properly and may even be dangerous. So what do you think? Or are...

diysolarforum.com

Fuse for continuous. 1.25 times the continuous amps.

Thanks!