Lambretta conversion

[Lammy]

That integrated pre charge/ disconnect is a nice solution. I think as you say I should try to build in as much headroom as I can sensibly into the system wherever there is a component choice that will allow that.

I am incorporating a switch, just to provide the option for swapping batteries, or away from vehicle charging. The pack size I can incorporate is not huge in terms of parallel groups due to packaging into the existing space, so the overall capacity is limited, approx max 3.6kwh so it would be helpful to have that option.
I’ve been looking for a bolt in fuse somewhere around 100 to 110vdc, I have found a motor home battery disconnect with a claimed rating to handle 300 Amps it is ip65 so that is a bonus although none of these components will be exposed to the weather and a 30w Vishay relay from Mouser.
The spec sheet for the BMS 20s 20p model states a continuous 200A and peak 350A rating so the fuse perhaps should rate at or slightly below 200A? Unfortunately there isn’t any detail that I can see the gauge of the built in cables but my plan was to use both B- and P- cables to carry current from the pack to the controller and to splice off a separate connection to the charger and to do the same for the + from the battery.
Thanks again this is really helpful.

 

[amberwolf]

That integrated pre charge/ disconnect is a nice solution. I think as you say I should try to build in as much headroom as I can sensibly into the system wherever there is a component choice that will allow that.

I am incorporating a switch, just to provide the option for swapping batteries, or away from vehicle charging. The pack size I can incorporate is not huge in terms of parallel groups due to packaging into the existing space, so the overall capacity is limited, approx max 3.6kwh so it would be helpful to have that option.
I’ve been looking for a bolt in fuse somewhere around 100 to 110vdc,

There should be some around, Bussman, etc., make them; high voltage ones may be sand-filled (or other nonconducting stuff that will fill in the hole left by the melted fuse lead, so that any arc could be extinguished better (no plasma conducting it, no arc)).

I have found a motor home battery disconnect with a claimed rating to handle 300 Amps it is ip65 so that is a bonus although none of these components will be exposed to the weather and

Battery disconnects have to handle cranking amps for the engine, so they have to be rated for that (if they're not, they'll fail in perhaps catastrophic ways while trying to start a "cranky" engine).

a 30w Vishay relay from Mouser.

What is the relay going to do? (sorry, I read all the threads each day and there's more than one I"m helping in with precharge/etc stuff, so I've forgotten and must have missed it in a lookback of this thread)

The spec sheet for the BMS 20s 20p model states a continuous 200A and peak 350A rating so the fuse perhaps should rate at or slightly below 200A? Unfortunately there isn’t any detail that I can see the gauge of the built in cables but my plan was to use both B- and P- cables to carry current from the pack to the controller and to splice off a separate connection to the charger and to do the same for the + from the battery.
Thanks again this is really helpful.

You cannot use the B- cable except to run from BMS to the battery cells, or else the BMS cannot do it's job of disconnecting the pack when limits are exceeded.

P- is the power output from the pack (pack negative, so P-) to the system. For BMSes with common C & D ports its' also the charging input.

B- is the power output from the battery cells (battery negative, so B-) to the BMS, and power input from the BMS to the battery cells.

C- is the charger input to the BMS (charge negative, so C-), for BMSes with separate C & D ports.

The BMS FETs are basically switches between each of those ports. (with limitations).

 

[Lammy]

There should be some around, Bussman, etc., make them; high voltage ones may be sand-filled (or other nonconducting stuff that will fill in the hole left by the melted fuse lead, so that any arc could be extinguished better (no plasma conducting it, no arc)).



Battery disconnects have to handle cranking amps for the engine, so they have to be rated for that (if they're not, they'll fail in perhaps catastrophic ways while trying to start a "cranky" engine).




What is the relay going to do? (sorry, I read all the threads each day and there's more than one I"m helping in with precharge/etc stuff, so I've forgotten and must have missed it in a lookback of this thread)



You cannot use the B- cable except to run from BMS to the battery cells, or else the BMS cannot do it's job of disconnecting the pack when limits are exceeded.

P- is the power output from the pack (pack negative, so P-) to the system. For BMSes with common C & D ports its' also the charging input.

B- is the power output from the battery cells (battery negative, so B-) to the BMS, and power input from the BMS to the battery cells.

C- is the charger input to the BMS (charge negative, so C-), for BMSes with separate C & D ports.

The BMS FETs are basically switches between each of those ports. (with limitations).

Sorry I didn’t realise you had posted! I really need to proof read my posts, I meant resistor not relay doh and that’s poor grammar on my part about the cable, what I meant to say was the BMS is a common port and has pairs of cables for B- and P- so I was going to use both P- cables to carry discharge current to the controller, in the manual they have the option to use one to take charging current.
So next time I will check my typing a bit better! I have worked up a design for all of this so I will post it up when I’m at my workstation.