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 > Voltage drop on inverter

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Itinerant1

Itinerant

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Posted: 08/14/19 10:44am Link  |  Quote  |  Print  |  Notify Moderator

BLF13 is that site talking specifically to a lfp dropin battery. You realize that within each of his drop in batteries there is bms that is cell balancing and if the cells drift outside their lvd/hvd it will shut his batteries down.

phemens

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Posted: 08/14/19 10:54am Link  |  Quote  |  Print  |  Notify Moderator

Yes, that was my going-in premise, that the BMS would take care of any per-battery specific issue.


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phemens

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Posted: 08/14/19 10:56am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

I still think a "circle" bus would be best, with the feed taken from the center of the disk and the 5 batteries equally spaced around the perimeter.


I think that's what I'm doing in essence, if all the cable lengths are the same that's what it works out to, if the diagram doesn't make that explicit.

CA Traveler

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Posted: 08/14/19 11:02am Link  |  Quote  |  Print  |  Notify Moderator

Based on the diagram I'd make 2 changes:

1. Change the wiring so that there is a maximum of 2 wires on any battery buss bolt.

2. Move the cutoff switch to the negative buss. When it's off then a short (like a wrench) from any positive post or wire to ground will not cause a problem.


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Bob


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Posted: 08/14/19 11:06am Link  |  Quote  |  Print  |  Notify Moderator

Here's my switch, battery buss bar not needed for balanced connection. AGM batteries so no concern about the shunt location.

[image]
[image]Click For Full-Size Image

BFL13

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Posted: 08/14/19 11:10am Link  |  Quote  |  Print  |  Notify Moderator

Itinerant1 wrote:

BLF13 is that site talking specifically to a lfp dropin battery. You realize that within each of his drop in batteries there is bms that is cell balancing and if the cells drift outside their lvd/hvd it will shut his batteries down.


No, it was about flooded batts.

Related? Is that rule for the battery fuse to be no more than 18" from the battery on the pos wire.

I was told at a car audio shop (which had big enough ANLs that I was looking for) that this rule came from car crashes. The battery can short and a fire start in the wiring to the audio amplifier (plus the other wires) back in the car somewhere. With the fuse there, only the 18" wire is not protected.


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Posted: 08/14/19 11:24am Link  |  Quote  |  Print  |  Notify Moderator

Well I can't remember any post of someone actually fusing all parallel batteries. More danger I'm sure walking on my street with no sidewalk.

BFL13

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Posted: 08/14/19 11:26am Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

Well I can't remember any post of someone actually fusing all parallel batteries. More danger I'm sure walking on my street with no sidewalk.


Theory vs practice! [emoticon]

phemens

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Posted: 08/14/19 11:38am Link  |  Quote  |  Print  |  Notify Moderator

I don't think I'd have room for all that anyways [emoticon] My storage bay is already pretty cramped with all h heavy gauge wiring as it is.
The fuse off the battery bus would be a couple of inches max, no worry there.
I can put the battery cut-off on either pos. or neg., I was always 'told' to put it on the positive side, but the possibility of shorting pos. battery to frame wasn't something I had considered (I do have battery post covers on all connections).

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Posted: 08/14/19 11:44am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:



I still don't understand why he wants the pos and neg links to the batteries to be equal. I get that all the pos links should be equal to each other and all the neg links be equal to each other. IMO the pos and negs do not need to be equal, since it is a circuit.
You are correct.

His method is less wordsmithing. And method 4 would be even more involved explanation.

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