[mitchhodge]

Hi all, This seems to be an ongoing issue but I'm still foggy. My conversion has a battery pack with eight 64v LG batteries for 500v.
I'm splitting them up with two fuses in a 3-2-3 manner. I have a DTI controller and Emrax228MV motor. The peak power is 124kw that puts me around a 250 amp max. As I understand, the eight batteries in series essentially makes them one big batteries voltage-wise.
The question is how do I size the fuses? Two 250 amp or two 125 amp?
It is a very basic truck. The only other loads are low voltage for the water pump, cooling fan, lights, etc...

 

[kennybobby]

What gauge of wire are you using and need to protect?

 

[mitchhodge]

50 mm wires which is equal to 1/0

 

[mitchhodge]

I'm seeing that 1/0 wire can handle 300 amps so a 250 amp fuse obviously will handle that. I'm new at this but if I put more than one fuse within the battery configuration, do each of the fuses need to be 250 or do I divide that by the number of fuses.
Thanks for reaching out

 

[piotrsko]

Each fuse needs to be sized for the wire rating. In your case one 250 rated DC. Do not parallel lesser value fuses to make up the fusing current since that causes erratic and dangerous behavior. Don't Ask me how I know. Also realize your 250 will probably allow more current than 250 to flow for a while until it melts. I use a 450 AND have documented 600 amps in the circuit for a monemt or so without failure. However it will still fail before the insulation melts

 

[mitchhodge]

The controller and motor is rated at 250 amps. That is where I"m getting the max. But thanks so much to both of the you for pointing that it is the wire being protected, as in house wiring. I've gotten way off track. So I'll be using the fuses to "break up" the assembly for safety while I'm working on it. To sum up, I'll be installing 250 amp fuses regardless of the number of fuses in the assembly. Feel free to correct me if I've missed anything. Again, thanks for info.

 

[remy_martian]

You need a fuse for each circuit (loop), rated for your peak pack voltage DC, at the power source so anything after the fuse is protected so it doesn't catch fire.

Do not go by ampacity of bare wire. You need the max current of the insulated cable you are using.

 

[mitchhodge]

Thanks for the info....It's clearing up things for me.

 

[cricketo]

Like Remy reminded, ampacity of the wire is typically tied to the insulation rating. Smaller wire will carry quite a bit of current without melting the conductor, but can fry the insulation and cause a fire. I often buy wire from this company, and they specify 285A max for their 1/0 AWG :

https://www.windynation.com/Welding-Battery-Cable/Windy-Nation-Inc/1-0-AWG-WELDING-CABLE-WIRE-RED-BLACK-GAUGE-COPPER-WIRE-BATTERY-SOLAR-LEADS/-/689?p=YzE9MjM=

 

[remy_martian]

Factor in the cost of turning a cable orange (split loom or tape, labor) if you decide to use black, red, or other cable colors for your HV runs on a roadgoing, or other, vehicle where first responders may get involved.

 

[kennybobby]

Here's a pop quiz related to a somewhat similar thread (nobody could provide an answer):

Factor in the resistance of the fuse, the contactor contacts, the terminal connectors, any jumper connectors, plus the resistance of the wire (all of these in series) and assume that this totals to 1 Ohm. Assume a diy EV build of a 360V pack which provides a current draw of 500 Amps (AC or DC motor). What voltage drop might you expect to see?

 

[cricketo]

I think that's an impossible circuit. In order for the draw to be 500A at 360V total circuit resistance needs to be 0.72Ohm.

 

[remy_martian]

Not only that, the power dissipation into one-ish ohm is horrific....

 

[catphish]

Factor in the resistance of the fuse, the contactor contacts, the terminal connectors, any jumper connectors, plus the resistance of the wire (all of these in series) and assume that this totals to 1 Ohm. Assume a diy EV build of a 360V pack which provides a current draw of 500 Amps (AC or DC motor). What voltage drop might you expect to see?

nobody could provide an answer

There's a reason for that

 

[piotrsko]

Which voltage drop where, battery or load?

 

[cricketo]

Which voltage drop where, battery or load?

Battery voltage will sag under load, but I think he was asking about an ideal circuit since that sag can't be determined from the data provided. Remy pointed an important point though - heat dissipation. If one's contactor has let's say 0.25Ohm resistance (arbitrarily accounting for 1/4 of the hypothetical resistance) at 500A that is 62.5kW of power being dissipated through such hypothetical contactor...

 

[remy_martian]

^ that's called, "welding"