Fuse recommendation for battery boxes

[phillipschip]

Hi,
I was hoping someone could recommend a fuse for each of my battery boxes. I will have two boxes, each with 5 x 39v LIfePo4 modules, in series to make a total of 390v fully charged at the motor (SDU). Currently I have a Tesla harness with the Pyro Fuse and box/connectors/long cables. I don't know much about that fuse, just that it has some Lithium Ion batteries in it, a ground, and some type of connector coming off it which I assume plugs into something in the Tesla that notifies when the batteries are low or fuse is blown. Not sure if I should just get another Pyro Fuse for the other box, or go with something different and less mysterious :0 Thanks for any help with this.

[nubster]

Hi,
I was hoping someone could recommend a fuse for each of my battery boxes. I will have two boxes, each with 5 x 39v LIfePo4 modules, in series to make a total of 390v fully charged at the motor (SDU). Currently I have a Tesla harness with the Pyro Fuse and box/connectors/long cables. I don't know much about that fuse, just that it has some Lithium Ion batteries in it, a ground, and some type of connector coming off it which I assume plugs into something in the Tesla that notifies when the batteries are low or fuse is blown. Not sure if I should just get another Pyro Fuse for the other box, or go with something different and less mysterious :0 Thanks for any help with this.

The white connector on the side of the HV Fuse box on the Tesla HV cables connects to a little "deadman" switch on the housing. If you open the fuse box, this switch will be released. Wire your contactor relay wires in series through this connector to implement an HVIL function. If you have a negative contactor (recommended), I would integrate it into that. This will ensure the contactor(s) open if you stupidly try to open the fuse box while the system is energized. https://www.diyelectriccar.com/threads/ ... le.208101/

[phillipschip]

Ah, ok. Could I put one of these at each of my two battery boxes ? Do I even need the fuse box, or can I just wire them without-easier to fit inside battery box.

[nubster]

Ah, ok. Should I just put one of these at each of my two battery boxes? Do I even need the fuse box, or can I just wire them without?

I would put a fuse in each battery box as close to the cells as possible, connected with bus bars, so the chance of a short in-between the fuse and cells is extremely low.

The fuse on the cable can only help if the short (or cause of overcurrent) is on the motor side of the fuse. If you get into an accident and/or the cables on the battery side of the fuse get damaged (causing a short), the cable fuse won't help.

I would connect the fused cable from the inverter to the primary battery box and then a non-fused cable from the primary to the secondary box and integrate dedicated fuses and contactors inside each battery box. I would design the system so that no HV leaves either battery box when the system is de-energized. I would use a cable fuse rated slightly lower than the battery box fuses so it pops first if the motor draws too much current, as it will be much easier to replace.

DISCLAIMER: This is not a recommendation. It is just my personal preference and opinion on how I would do it if it were me based on my imperfect understanding of things.

[phillipschip]

That sounds just like what I was thinking. My main question at this point I guess is: Could I use Pyro Fuses for all that-no fuse box for the ones inside the boxes? They are pretty cheap. Any other fuse rated as such looks to be hundreds of $ each.

[uhi22]

I would recommend to study the data sheet of the pyro fuse. My understanding is that the pyro fuse is designed to be externally triggered (like an airbag) in case of a crash. In contrast, a normal fuse is controlled by the flowing current. Maybe there are devices that are specified for both cases.

[phillipschip]

From what I understand, the Pyro fuse is triggered more abruptly at overcurrent than a normal fuse that can take quite a bit of overcurrent for some time before melting. I also read somewhere that when triggered it keeps some low power to get to the side of the road and protect the inverter. Not sure about any of that though :0

[phillipschip]

I found these fuses at Ev West for $79:

https://www.evwest.com/catalog/product_ ... cts_id=711

Rated at 500v and 600a continuous, 900amp peak. I could use one of these on each of my battery boxes and keep the pyro fuse for the motor.

[jrbe]

From what I understand, the Pyro fuse is triggered more abruptly at overcurrent than a normal fuse that can take quite a bit of overcurrent for some time before melting. I also read somewhere that when triggered it keeps some low power to get to the side of the road and protect the inverter. Not sure about any of that though :0

Pyro = airbag like explosive device to cut the battery connection. This is likely blown by the airbag computer over some level of impact.
What's your plan to trigger it in your conversion?
How are you determining when that's needed?
This is very likely overcomplicating things for you. I'd strongly suggest skipping the pyrofuse idea.

I think you're confusing a mild isolation monitor fault allowing you to get off the road. This is watching high voltage to the chassis of the car and warns to cuts the battery power off depending on how bad it is. It's watching if there's too low of resistance from the high voltage battery to the chassis.

A pyrofuse blowing is essentially instant.

You would never want a fuse to half blow, if something is very wrong you want the fuse to open immediately.

A fuse is to protect the wires or the battery. Do not think a fuse will protect your motor or inverter, this is incorrect.

[phillipschip]

From what I read, the HV pyrofuse doesn't communicate with anything in the car-it's just a fuse triggered by overcurrent. There is another pyrofuse for the 12v system hooked to the air bags in case of accident. The OEM harness with the correct connectors for my SDU that I got on eBay has a pyrofuse/box between the motor and the negative battery terminal. Should I cut this out? I was thinking about checking to make sure it is the newer version without batteries and just keep it in the loop, then fuse each box with the fuse from ev west that I linked. However, if it isn't needed I could just loose it to make things more simple.
I have an IMD on order and will be installing that too per NHRA requirements.