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Battery Disconnect - Latching Relays
#1
Was wondering if there was a general consensus on what to use for a battery disconnect (OV & UV protection)

Latching relays in the 200A range aren't exactly common - so I was wondering what others recommended.
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#2
A disconnect is a disconnect and for that I would not use relays. I would use a breaker of some kind. In my case i use Breakers with trip function like an ABB S5N or S3 series

Just make sure you get one rated for the voltage you need at DC and not just AC!
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#3
Thanks for getting back to me! I guess I'm a little confused as to why - If a latching relay/contactor is rated for continuous duty at 200A DC, why would I use a breaker and then have to trip it via microcontroller for an undervoltage condition?
I don't know enough about the difference to understand why one would be chosen over the other.
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#4
(01-23-2019, 06:48 AM)Mikethezipper Wrote: Thanks for getting back to me! I guess I'm a little confused as to why - If a latching relay/contactor is rated for continuous duty at 200A DC, why would I use a breaker and then have to trip it via microcontroller for an undervoltage condition?
I don't know enough about the difference to understand why one would be chosen over the other.

You would need to control the latching relay somehow as well.....
A breaker would also be an over current protection device.
A breaker would need to be manually reset, ie you could not get a switch on/off cycle going.
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#5
The reason for a breaker is as redpacket said. Its one way kind of so you know its off when its off. Thats the main reason you do shut it off right? last protection if neededn.

Using relays that you do when you should via a system switch somtehing on again but I do not see the use in a powerwall for that. The software on the gear should act as the on off instead.
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#6
I was thinking it might be needed if a single with a lower capacity was rising in voltage faster than the others - you would turn off current into the system until equalization was done - then allow current back into the battery pack to finish charging. I'm realizing at this point, that was a probably insane thought - balancing shouldn't work like what I was originally thinking.

Is there a breaker with external tripping functionality that doesn't cost so darn much? Even used ABB breakers are nearly $200
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#7
You can pick up ABB breakers used for cheap, they certainly are not $200. Some of the lower amp ones are $60ish. I just bought an ABB DC 300A breaker for $90 shipped.

Check some of these listings on eBay... https://ebay.to/2DvVRPn
BRAND NEW: LiFePO4 26650 Cells! Starting at $2.50 each!!
^ Use coupon code "powerwalls" on checkout for a 10% discount
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#8
Does not have to be ABB only, any top brand manufacturer will do the job as long as it is rated for DC and the needed Ah. For instance the NS250N from Schneider can be found at very reasonable prices and it is rated up to 250 VDC and 250A. Just do not rush it and wait for the right deal.
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#9
Ahh, I see now. Thanks for the heads up, yeah looks like I can probably get one around the $60 range.

Just wondering - Since I'm also working on a BMS - are most of these tripped by 24VDC? Is that a standard trip voltage for these breakers?
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#10
The Schneider I mentioned avobe uses a 220 V coil for tripping, at least the one I got in EU
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