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Battery fuses

SD_DRACULA

I have seen a few installations, usually with the pylontechs that use this fuse/disconnect https://shop.shortec.com/eaton-moeller/ebh00o3tm8-size-00-hor-fsd-mount-plate-m8-screws/ and 80A fuses with it.

My question is, if the inverter can do 100A charge/discharge, will that not trip it and fuse(s) higher than 100A, i.e. 125A should be used?

Or maybe that's fine since it can do continuous 160A current?

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reklamos

You need to look at the whole setup but in general fuses are there to protect the wires and should be rated accordingly. It is not only charge/dischage currents that should be looked at.

SD_DRACULA

I believe the cables usually are 25mm2 if I'm not mistaken.

reklamos

here is a good article about fuse wire and fuse sizing for DC systems. It has also charts. It uses AWG for wire sizes but google has plenty conversion charts.

SD_DRACULA

https://www.boards.ie/discussion/comment/118773934#Comment_118773934

Where? 😂

I think it's pretty straight forward what I need to do, the battery cables are 25mm2 and I need another set of them so one connects to the fuse/disconnect/breaker and the other end from that to the inverter, i.e. this:

reklamos

sorry here is a link

Diagram looks fine, this is I how my pylons were connected.

SD_DRACULA

Thanks and yeah 25mm2 needed for 100a and that's what the supplier has for these batteries which spot on.

I assume that fuse disconnect above needs two fuses, and both + and - cables get connected to their own pole on the switch

reklamos

You only need 1 fuse on positive line, there is no need to have 2. Also if there is circuit breaker I do not think that fuse is required as they both serve the same purpose, the only difference is that fuse is sacrificial device. Now it is up to debate which is batter.

SD_DRACULA

Looks like in the official install guide it does show a breaker with both +/- cables going through it, not the fused disconnect so maybe that one?

Which type would be required, I would guess a DC type and 125A rating since it will be used at 100A charge/discharge?

reklamos

DC breakers have both +/- cables going trough. This does not apply to fuses though. High amp DC breakers are not very common and can be expensive. I got 100A from midsummer. I have not seen 125A for sale but I see that projoy do manufacture them so you may ask midsummer if they have any.

SD_DRACULA

Yeah proper DC breakers like the Noark 125a is between 400-600 but I did check with midsummer and they did say the 100a one they sell will cover my needs and they are preferred over the fuse ones.

Looks like solartricity do the 125a one as well.

the_amazing_raisin

Wouldn't a few mega fuses be just as good and a lot cheaper? You can pick them up for a few euros so you can have some spares handy

E30M3

https://www.boards.ie/discussion/comment/118797915#Comment_118797915

I understand that with DC Voltage Breakers/Fuses are critical as DC Higher voltages may ARC and also up to about 10 Amps they are relatively cheap and available but get quite expensiver and specialised for higher ratings.

the_amazing_raisin

Still not quite getting the specific requirements here, you can get DC MCBs for a few euros as well

https://www.bimblesolar.com/extras/dc-circuit-brakers/125a-din-breaker-tomzn

Do they need to be a specific type of fuse?

reklamos

https://www.boards.ie/discussion/comment/118799143#Comment_118799143

This is single pole breaker hence it is cheaper. It may work perfectly fine. I use double pole. My aproach is not to try to save on safety.

Here is good example of cheap one: https://www.youtube.com/watch?v=2TJEzdqtXlQ

SD_DRACULA

For sure, go with what the installer/suppliers recommend

the_amazing_raisin

I was reading through the Pylontech manual and noticed the cables to connect the batteries to inverter are rated for 100A

So if you've 8 batteries you're limited to 4.8kW discharge because of the cables, right?

I wonder would it be better to connect the batteries to a DC busbar in groups of 4 each through it's own 125A fuse, then a 250A fuse on the busbar connection to the inverter?

SD_DRACULA

Highest Solis hybrid inverter (single phase) will only charge/discharge at 100A so why does it matter if you can't go higher?

The cables are 25mm2 if I recall and that can do more than 100a ofc but you'd need an inverter/charger that can go higher anyway

the_amazing_raisin

I was looking at an 8kVA Victron which can pull more than 100A

Victron actually provide an integration guide for Pylontech and I noticed in the diagram they have the batteries in groups of 4 wired back to a busbar before going to the inverter

I might check this with them, did they just put it in by coincidence

munsterfan2

Hi, installer left me equipment for battery install as he didnt have one in stock, since ordered via aliexpress, Tried googling the fuses & box in image, trying to confirm if they are for the DC between battery and inverter. Is that correct ?

irishchris

https://www.boards.ie/discussion/comment/118804629#Comment_118804629

Yes that is the battery fused disconnect.

the_amazing_raisin

So I think I found the answer to going over 100A with Pylontech batteries. The manual for the US2000B says to connect a second set of power cables to the first and last battery

So you'd have 2 positives and 2 negatives coming from the battery to the inverter

From what I can tell the Pylontech BMS calculates the max current by the number of batteries in a group. So 8 batteries will allow 200A nominal discharge regardless of the battery cables

I spoke to someone at Victron and they said the groups of 4 connected to a busbar are preferable to stop a lot of current going through the first and last battery

I'm not really sure that's a problem, but I can see if being better from a fusing standpoint. If you have a group of 8 with 2 sets of cables, then you'll need each set to go through 125A fuses. But if the resistance of the cables isn't equal then more current will flow through one path and might pop the fuse even if the battery was well within limits

Having separate groups each with its own cables and fuses back to a busbar gets around this problem

SD_DRACULA

Yeah and if you watched any of Will Prowse's videos he does a test where he parallels a few batteries and uneven cable lengths will have an impact to the "furthest" batteries, they will charge slower than the first ones.

Basically use the same type of cable and lengths and also bus bars. If using those short daisy chain pylons cables it will be fine I'd say but the 2 positive and 2 negative long cables should be the same length as well.

Or you could just buy 4 of the new US5000 batteries and stack them on top of each other and not have to deal with two stacks of 4 x 2.4

the_amazing_raisin

I've seen similar stuff mentioned in this book

https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

Definitely a must read for anyone designing a system

I would imagine using the cables supplied by Pylontech they should be well matched, but better to avoid the possibility of imbalances as much as possible

PS, I know I keep mentioning Victron stuff, I'm not affiliated or anything, I just think they've one of the best knowledge bases around 😅

reklamos

https://www.boards.ie/discussion/comment/118804629#Comment_118804629

Fuse looks ok. If you looking for more than 100A then you will need 00 size fuses but these will not fit into fuse disconnect. Here is a link for fuse specs. Google for part number and you will find then online also.