How do I connect a high current relay?

[Unclebob]

Ok, this might be a bit of a noob question but I don't want to set my car on fire so here we are! I picked up some relays for my latest project and the bloke at the shop tried to convince me that I should use some of these yellow quick connects. I already had a few floating around at home so I didn't buy them, but something just seems a little off here.



None of these quick connects seem to have an amp rating. The cable that went to my aux battery (now DC-DC charger, thanks for the writeup @Delmassive) is something like 10mm and had an 80A fuse and 100A relay, with a cable run length of I guess 2-3m. This is probably going to be about 2m, and needs to handle up to 120A comfortably (it'll have a 120A breaker). It's going to have a 120A Anderson connector which looks far more robust than these little connectors. The point just above the insulation where it flares out is tiny (either side of the hole is about 3mm and about 0.5mm thick so very roughly 3 mm2 cross sectional area) and aluminium, not copper like the connector on the original relay holder. I haven't been able to have a good look at the original connector because it's stuck inside the holder, but I'd expect something a bit beefier. Am I unnecessarily worried here or is there a better option?

Great segue - are the relay holders like the one used by the stock aux battery charging relay available generally (if so, what are they called?) or are they a VW special? I've got a lot of spare slots under both seats I'd prefer to use rather than figuring out an alternative mounting solution. I'd need SPDT rather than SPST like the original one.

datasheet for the relay: https://www.jaycar.com.au/medias/sys_master/images/images/9671127662622/SY4073-dataSheetMain.pdf

 

[Deaky]

I’d use something like this 12V 200A Heavy Duty Relay

 

[Loz]

Out of interest, you say you have a DC-DC setup, so what will this relay be used for?

 

[Unclebob]

Hmm, this does seem like a better option. How silly of me to assume that if I can buy a 150A relay, I'd be able to connect to it -_-

I've got a 100Ah battery under the passenger seat but a much larger (and heavier) 400ah removable battery bank. I'm working on a way to be able to put the removable battery bank in the back, hook up a single Anderson plug, and (eventually) it'll become a single 500Ah battery bank without setting my car on fire if one is full and the other is flat.

This is all Renogy kit so the plan is to use the serial interface to monitor the state of charge of the batteries and use the dc-dc charger to bring the voltage of the lower one up to match the higher one, then join them together.

Tbh it's very unlikely there will ever be 100A going through the relay unless I stuff up the control of the relay (which is more what the breaker is for). I'd have to be drawing 500A from the stuff hooked up to the removable battery side, but I want the BMS to shut the battery off before the breaker trips (separating the bank), or there's going to be a big jump in the draw on the removable battery which would already be pushing beyond its limit. I'm also going to have load shedding as the state of charge drops (the nice to haves get shut off so that the fridge gets to run longer) - I could probably use this to start ditching load if it gets anywhere near that high.