Breaking on the negative pole has the potential to induce an inductive response on the upstream side of the circuit if you interrupt while there's significant current flowing.
As such I wouldn't recommend it.
Breaking on the positive pole on the other hand basically leads to brownout in the downstream systems which definitely preferable.
If you're stuck with breaking on the negative pole then I'd put in some appropriately rated clamping(TVS) diodes to in there so that any such spikes don't exceed the ratings of any other connected hardware.
Breaking on the negative pole has the potential to induce an inductive response on the upstream side of the circuit if you interrupt while there's significant current flowing.
As such I wouldn't recommend it.
Breaking on the positive pole on the other hand basically leads to brownout in the downstream systems which definitely preferable.
If you're stuck with breaking on the negative pole then I'd put in some appropriately rated clamping(TVS) diodes to in there so that any such spikes don't exceed the ratings of any other connected hardware.
I'm trying to determine if I am stuck or if I can fit it to the positive lead or it has suitable safety hardware built in. I bought a BMS24t which looked good with all the bells and whistles and within my budget. They also offered a DCC300 contactor that replaces two contactors. I only realised after the fact I shouldnt have a circuit breaker on the negative side which the DCC unit suggests. It does say it has inbuild safety protection but Im yet to get an answer from the owner. There's a link if you're interested in having a read.
Last edited by Podbuilder; 29 October 2020 at 0447.
Hmm... from the reading of that it appears that it has some form of built-in inrush limiting, so it's not out of the question that it has TVS in there too but it doesn't say anything about it which I'd expect it would.
That being said, I don't see a break rating in there either which suggests to me that this thing is only designed to be used to open and close under no-load conditions - as long as that's the case then you can put it wherever you like.
The potential to induce an inductive response it linked solely to opening operation while the circuit is under load; so turning off the ignition which accelerating or decelerating hard basically. Even in that circumstance, if the break rating is low you may well find that the magnetic aligning force on the contacts simply won't let the circuit release until you're below the danger zone (this won't be by design, more a function of not being designed as a 'breaker').
Hmm... from the reading of that it appears that it has some form of built-in inrush limiting, so it's not out of the question that it has TVS in there too but it doesn't say anything about it which I'd expect it would.
That being said, I don't see a break rating in there either which suggests to me that this thing is only designed to be used to open and close under no-load conditions - as long as that's the case then you can put it wherever you like.
The potential to induce an inductive response it linked solely to opening operation while the circuit is under load; so turning off the ignition which accelerating or decelerating hard basically. Even in that circumstance, if the break rating is low you may well find that the magnetic aligning force on the contacts simply won't let the circuit release until you're below the danger zone (this won't be by design, more a function of not being designed as a 'breaker').
Lots to take in here. I better read up on contactors so I have a better understanding of there specs. They are sold in differing amp ratings so you'd assume he's selling a functional product. But I'll ask the questions. I dont wish to damage a $600 controller.
Chargery's reply. "your consideration is correct, DCC is built-in arc-suppression circuit, generally, the DCC should be installed on the positive, but the DCC has mosfet, don't drive it on positive." So on the negative wire it goes.
Yeah that makes sense now alright - sounds like they've an N-channel FET driving the contactor coil.
Assuming your HV and 12V circuits aren't isolated, you likely need the voltage at the common terminal of the contactor to be less than ~10V for the 12V circuit to be able to run it.
If there's arc suppression built in there then it's less likely that you'll provoke an inductive response in the circuit - precisely how likely depends on the nature of the arc suppression circuit, but it does mitigate the concern to a degree.
As to whether or not is a 'functional product' I've absolutely no doubt that it is - the only question is what is it designed to do.
From my reading of it, it seems like that thing is designed to close on an inductive circuit without welding itself (hence the inrush limiting) and has a thermal rating appropriate to sustain a 300A load.
What it does not appear to be designed to do it to break/disconnect under load. This isn't a bad thing, it's simply not a part of its feature set.
More often than not, the price of switchgear is more heavily linked to its break rating than it's thermal rating; so this isn't to be unexpected in cheaper kit.
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Originally Posted by Spoonman
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