Need help! 48 volt caught fire

7TZ

New Member
Hello, I need help I put together a 48 volt 3.2V 120Ah Lithium Iron Phosphate LiFePO4 battery pack. I had bms all hooked up everything was reading good I got 52 volts, i connected it to my growatt 3k all in one based off the blueprint on the mobile solar sight the only thing I had different was a 48 to 12 conversion box for my tong jack. I used a pre charge resistor no sparks when I connected everything then 30 seconds later sparks flying and one batter catches fire. The ground wire to the converter melted off, I’m not sure what I did wrong or where I should go from here are all the cells bad or just the ones that leaked? Where do you think I went wrong on my wiring. Please help!
 

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Terrapin

Solar Enthusiast
Oh man I am so sorry. This stuff is all new to me so I have no help to offer, just sympathy and thanks it wasn't worse!
 

Boondock Saint

Solar Addict
Your DC-DC converter is only rated for 30A. My initial guess would be that your 12v batteries were basically dead and had a high demand, or you had such a load on your 12v system that it far exceeded the 30A supply.

If at first you don't succeed, fuse, fuses again.

I think it's recoverable in a fairly inexpensive way. If I were to rebuild I would redo the cables and lugs and not initially incorporate the DC-DC converter. Stand up your other systems and gives things time to operate and level out. Then after a couple of days of otherwise normal use, tie in the DC-DC converter with it's own fuses and shunt and measure the draw across the line IN and OUT of the converter.

Wear safety glasses. Have fire extinguisher.
 

wholybee

Solar Addict
Sorry about the mishap. The drawing for the voltage converter doesn't have a fuse in it. It really needs one. In your picture it looks like you tried to use a circuit breaker, and (if I am seeing it right) it is all wrong. For some odd reason, the converter seems to use black as positive and yellow as negative. You connected black to the chassis/frame, which would be a direct short. You also connected the negative input wire to the same terminal as the output positive wire.
If you redo this, instead of a circuit breaker, use 2 fuses. Put one fuse in the red wire, and the second in the black wire that is the positive output. Don't cross-connect the input and output in any way.
 

7TZ

New Member
Thank you everyone for your advice. I think my issue is the converter, it shows the yellow it + load and the red is + battery both black as - or ground. This might be a dumb question but what kind of inline fuse would you guys recommend I be using on a 48volt connection for the converter? I ordered 3 more cells and am going to give it another shot when they arrive, I want to make sure I get it right this time. I’m going to order another converter any recommendations, the only thing I need the converter from 48v to 12v is for it lights (for when the inverter is off) and for the tongue jack. I have the inviter wired into the ac input on the main breaker box so that should control everything else. Thank you for your help everyone I really appreciate it!
 

OnTheRoadAgain

Solar Addict
Man, that kind of stuff can be nerve wracking. Sorry you had to experience it.
It does serve to remind others to take all precautions so some good comes from it.
I would think ANL or Mega Fuses would be good.

Good luck
 

wholybee

Solar Addict
I see now (if I zoom in) that yellow is positive and black is negative. The battery in the drawing is connected wrong then. I still think the issue is related to the breaker connections.

The fuse needs to be smaller than the max current the wire can handle without melting and burning up. I don't know what size wire you used, but that is what dictates the fuse.
 

7TZ

New Member
So I ordered a 30 amp ANL fuse for the converter and was thinking a 100 amp ANL fuse for the main positive that goes to the growatt. Should I do anything different? Thank you all again
 

Zwy

Solar Addict
So I ordered a 30 amp ANL fuse for the converter and was thinking a 100 amp ANL fuse for the main positive that goes to the growatt. Should I do anything different? Thank you all again
Have you actually measured the startup amp load of the jack? The usual amp clamp many use here won't show the amp surge at startup, you really need a graphing meter.
 

G8trwood

Solar Enthusiast
My cargo trailer jack is 30 amp. They put it on a 40amp circuit and said it would blow a 30amp circuit. Whether this is your issue or not....
 

Supervstech

Administrator
Staff member
Moderator
I don’t think you have the converter wired in properly...
looks like you have the input and output positives wired to the same post...
 

Supervstech

Administrator
Staff member
Moderator
I am amazed the converter wiring could but pan up the cell cable connection.
Can we see a full wiring picture of your setup, see what is wired wrong.
That picture of the converter to battery certainly is not correct.
 

Bud Martin

Photon Sorcerer
Picture #2 show + of the Load connected to the Black wire (-) of the buck converter, the - of the Load is connected to the Yellow (+) of the buck converter, that is wrong.
 

mikefitz

Solar Addict
It seems there was a direct short on the battery or part of the battery. No fuses and no BMS? You say there was a BMS, it should have shut down with over current.

The wiring diagram for the converter seems to have the load connections incorrectly labeled, does not inspire confidence in the product.

If the converter is rated at 360 watts, with a 48v input ( assuming the converter is a 48 to 12 unit) you will need a 10 amp fuse, or perhaps higher at 15 amps, at the battery on the input cable. A fuse for the output, say 40 amp for the load, would be advisable.

This issue shown the importance of suitable fuses or breakers in a system.
Fortunately nobody was injured.

It would be helpful if a connection diagram were made available.

Mike
 
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7TZ

New Member
I just took it all apart to remove the bad cells, I have the the negative coming off the bms going to a bus bar and the positive off the batteries going to a bus bar. From the bus bars I have one positive and one negative going to the growatt and on positive and one negative going to the converter. From the converter I had the red wire going to the positive bus bar and the negative to the negative bus bar the the yellow going to a 40amp circuit breaker the negative ground on the frame. From there I have the main 12volt positive for the trailer connected and my tong jack positive.
 

chrisski

Photon Sorcerer
So I ordered a 30 amp ANL fuse for the converter and was thinking a 100 amp ANL fuse for the main positive that goes to the growatt. Should I do anything different? Thank you all again
My Blue Sea ANL 200 amp fuse is only rated for 32 volts, less than your 48 volt system. Check the voltage ratings of the fuse. As far as the amperage, I did a bit of calculations for my loads before I chose the 200 amp fuse. Really based off the highest wattage I wanted my inverter to deliver after calculating everything wired to it and the wiring could withstand more than 200 amps.

Unfortunately the fuses I deal with are ANL and Maxi fuses, and those max out at a 24 volt system, which a 32 volt max is good for most chargign profiles on 24 volt systems. I think the problem with going a higher voltage than the fuse is rated for with a DC system, the fuse could blow at 30 amps, but continue to ARC across the open fuse. I was surprised when I did an amp test on my 48 volt panels at 3 amps, and the current arced over 1/4 of an inch. That is less than disintegrates in most fuses I have blown.

The AIC rating becomes important also. That ANL fuse I use has a 2000 AIC rating. Even in the voltage were less than 32, that ANL may not be good for lithiums because they deliver so much amperage.
 
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7TZ

New Member
This is a picture of the actual inverter I used, it’s a 48 to 12
 

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GXMnow

Photon Sorcerer
I see one serious mistake in the second picture. It shows the black output wire of the 48-12 volt converter going to the load + OUCH!
It looks like you had the fried black wire was also connected to the yellow wire. The two black wires are internally connected together, I have one of those also. That looks like a dead short.
 

7TZ

New Member
I am using a overkill BMS for 48volt not sure why it didn’t cut off
 

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