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 > Voltage drop on inverter

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BFL13

Victoria, BC

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Posted: 08/13/19 07:41am Link  |  Quote  |  Print  |  Notify Moderator

The smartgauge fan method mentioned earlier might actually resemble your buss method.

The fuse is to protect the wire, but which wire? It is the long one after the fuse to the inverter. The short wire from the fuse to the battery is not protected. With the buss method, if the fuse is on the inverter side of the buss, that is more wire not fused. Seems you need a fuse for each battery between battery and bus?

The one wire from buss to inverter must be gauged to carry all the amps total of the amps from the various wires into the buss. Charger plus solar one way and inverter plus other 12v the other way, whichever has more amps total. It needs a big fuse, while the wires into the buss need to match the gauges of their wires.

Yes you can parallel the fuses and also the wires. Some inverters have two pos and two negs for DC input. You can use one fat wire or two thinner ones. Fusing can be one big one or two smaller ones and you can use two smaller ones even if you use one fat pos wire.

With such high amps to fuse for with those fat wires, my inverter would hit the low voltage alarm and shut down before the amps could be as high as your fuse rating. With Li batteries and such low voltage drop, your inverter might not be triggered to shut down, so the fuse is even more important.

I do not use the inverter rating to decide on wire gauge, but instead use the max loading, which treats it as a lower watt inverter in effect. So I use thinner wire. BUT that thinner wire is still fused for its own gauge, so it works out.

Just don't overload the inverter past what you planned or else now instead of the inverter's own overload shut down, you will blow the fuse.

I suggested bunching batteries. ISTR (could be wrong) there are "issues" paralleling so many batteries, but that might have been solar panels (or both cases). So you can limit the number in parallel by bunching.


1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
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53chevy

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Posted: 08/13/19 03:14pm Link  |  Quote  |  Print  |  Notify Moderator

MEXICOWANDERER wrote:

Telephone and talk to Blue Seas Systems. They have their act together when it comes to supplying what you need. Phone: +1 800-222-7617

A direct continuous short can blow your batteries to shreds. Ignite your inverter and a bunch of other nasty deeds.

They say and I agree CLASS T fuses are the proper way to fuse ANY inverter. I learned this 30 years ago from Trace Engineering. But Blue Seas will set you straight.

Circuit breakers have a specific use for a specific application and PROTECTING ELECTRONICS is not on that list.

Hope this helps


I apologize for hijacking this thread. I'm looking to get about a 2KW inverter, I called Blue Sea and was told the class T fuse size depends on the inverter input specs. None of the inverters I look at online give that particular spec. Am I not looking in the right place?


Allan

BFL13

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Posted: 08/13/19 03:23pm Link  |  Quote  |  Print  |  Notify Moderator

At 2000w, DC amps draw will be about 200a (divide by 10) Surge rating 4000, so 400 amps

phemens

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Posted: 08/13/19 05:47pm Link  |  Quote  |  Print  |  Notify Moderator

Ok, so if I follow method 3 in the Smartgauge example, I am back exactly to my bus layout.

Here is a diagram I drew up to illustrate. The only change from the previous layout would be moving the fuse to in-between the buses (pos. battery bus & pos. distribution bus).

[image]
(Drawing modified based on comments)

* This post was edited 08/14/19 05:55am by phemens *


2012 Dutchman Denali 324LBS behind a 2006 Ford F-250 V10 out of Montreal
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1Kw solar, 500 AH LIFePO4, Yamaha EF2000 gen, Samlex 3000w Inverter

BFL13

Victoria, BC

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Posted: 08/13/19 06:10pm Link  |  Quote  |  Print  |  Notify Moderator

I am not clear whether you have allowed for the proper method of fusing "branches" and the output of a bus to total the amps of all the branches. I assume there are branch fuses not shown: inverter to bus, MPPTs, RV, Victron positive?

This is very good at explaining it all. Worth a look!

http://www.bcae1.com/fuses.htm

I see two batts "bunched" and three separate. I still think 2 and 3 bunched is better, but no proof to hand.

pianotuna

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Posted: 08/13/19 06:43pm Link  |  Quote  |  Print  |  Notify Moderator

Your diagram is not balanced.

All the battery leads need to be identical in length.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

phemens

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Posted: 08/14/19 05:32am Link  |  Quote  |  Print  |  Notify Moderator

pianotuna wrote:

Your diagram is not balanced.

All the battery leads need to be identical in length.


Yes, that's not clear in the diagram, all the cable lengths from the batteries are equal length. I updated it to reflect that and other comments.

* This post was edited 08/14/19 05:55am by phemens *

phemens

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Posted: 08/14/19 05:35am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

I am not clear whether you have allowed for the proper method of fusing "branches" and the output of a bus to total the amps of all the branches. I assume there are branch fuses not shown: inverter to bus, MPPTs, RV, Victron positive?

This is very good at explaining it all. Worth a look!

http://www.bcae1.com/fuses.htm

I see two batts "bunched" and three separate. I still think 2 and 3 bunched is better, but no proof to hand.


The 2 batteries are not bunched, the drawing software insists on overlaying the lines, they each have their own run to the bus, but share a lug. I'm not sure I understand why fuses would be needed between each battery and the bus if the bus overall is 'protected' by the fuse between the buses?

Thanks for the link!

pianotuna

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Posted: 08/14/19 09:53am Link  |  Quote  |  Print  |  Notify Moderator

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.

BFL13

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

I stole this from a site:

"With a parallel battery bank, one fuse is adequate for protecting the wiring against load overcurrent (between the parallel-connected batteries and the load), but we have other concerns to protect against as well. Batteries have been known to internally short-circuit, due to electrode separator failure, causing a problem, not unlike that where batteries of unequal voltage are connected in parallel: the good batteries will overpower the failed (lower voltage) battery, causing relatively large currents within the batteries’ connecting wires. To guard against this eventuality, we should protect each and every battery against overcurrent with individual battery fuses, in addition to the load fuse..."

"Bunching" is Method 4 in this link, except with 5 batts it would be with 2 and 3.

http://www.smartgauge.co.uk/batt_con.html

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.

* This post was edited 08/14/19 10:25am by BFL13 *

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