Battery-inverter cables upgrade

[pudding]

I've just changed my inverter to a 5kW Sunsynk upgrading from the 3.6kW version.

I've still got the same cabling to my 6 Pylontechs, going with 2x25mm cable from inverter - 100A Jean Muller Disconnector - 2x25mm Pylontech cables - 6x3000C.




Obviously, with these cables still in place I'm still limited to max of 100A and cant use the full 5kW rate to the battery stack yet, and I've limited the charge/discharge rate in the new Sunsynk to 95A. I want to get these cables/disconnector changed to both handle more from the 5kW Sunsynk, but also prepare for swapping out the Pylontechs for 2 of the Seplos Mason DIY kits (https://www.fogstar.co.uk/collections/s ... e-a-bundle).

So, what the best way to do this and what do I need? I'm thinking I'll need to bump up to 2x35mm cables from inverter to the DC disconnector with new fuses (160A? - https://www.bimblesolar.com/index.php?r ... Yk_FaXfahK), 2x35mm to a connector block such as this - https://www.electrical2go.co.uk/70mm-1x ... gIGG_D_BwE, then 2 lots of 2x25mm or 1 lot of 2x35mm cables to the actual batteries?

Any tips or suggestions for best places for cables/fuses/connectors/crimps etc would be great.

[Stinsy]

I've just changed my inverter to a 5kW Sunsynk upgrading from the 3.6kW version.

I've still got the same cabling to my 6 Pylontechs, going with 2x25mm cable from inverter - 100A Jean Muller Disconnector - 2x25mm Pylontech cables - 6x3000C.




Obviously, with these cables still in place I'm still limited to max of 100A and cant use the full 5kW rate to the battery stack yet, and I've limited the charge/discharge rate in the new Sunsynk to 95A. I want to get these cables/disconnector changed to both handle more from the 5kW Sunsynk, but also prepare for swapping out the Pylontechs for 2 of the Seplos Mason DIY kits (https://www.fogstar.co.uk/collections/s ... e-a-bundle).

So, what the best way to do this and what do I need? I'm thinking I'll need to bump up to 2x35mm cables from inverter to the DC disconnector with new fuses (160A? - https://www.bimblesolar.com/index.php?r ... Yk_FaXfahK), 2x35mm to a connector block such as this - https://www.electrical2go.co.uk/70mm-1x ... gIGG_D_BwE, then 2 lots of 2x25mm or 1 lot of 2x35mm cables to the actual batteries?

Any tips or suggestions for best places for cables/fuses/connectors/crimps etc would be great.

A few initial points:
- You are skating on thin ice! The pylontech cables are already 2m (IIRC) and you're adding another 1m of 25mm² as well as the termination points and fuses. That's a fair amount of voltage drop (and therefore heat).
- Any cable bought from eBay/Amazon (or even some reputable suppliers) will not be as advertised. It'll be at least one size smaller!

The easy way to improve connection to the Pylontechs is to use two sets of cable to double-up on the stock 35mm² to the batteries. This isn't just saving the cables but also the connectors. You can then terminate those in a NH1 2-pole fused disconnect and have a short length of 70mm² (or whatever you choose) going from the disconnect to the inverter.

[pudding]

Thanks for the reply. Do you mean the current setup is skating on thin ice, or the proposed changes would be? Currently yes as you say, it appears there's maybes 3m of 25mm cable handling up to 95A.

I think the current 2m Pylontech cables are just the standard ones that are 25mm2, so should these be 35mm2 versions currently you think? I can swap to 2 lots of 35mm cable from Pylontech to disconnect no probs though.

Also, why does the fused disconnect unit need changing to the nh01 type you mention, rather than just switching the nh00 fuse out for a larger 160a one?

[Stinsy]

Thanks for the reply. Do you mean the current setup is skating on thin ice, or the proposed changes would be? Currently yes as you say, it appears there's maybes 3m of 25mm cable handling up to 95A.

I think the current 2m Pylontech cables are just the standard ones that are 25mm2, so should these be 35mm2 versions currently you think? I can swap to 2 lots of 35mm cable from Pylontech to disconnect no probs though.

Also, why does the fused disconnect unit need changing to the nh01 type you mention, rather than just switching the nh00 fuse out for a larger 160a one?

Don't get me wrong. I'm not suggesting your current setup is "bad" or "dangerous", just skating close to the wind!

3m of 25mm² at 100A and 48V is a voltage drop of 0.462V or 0.963%. If you consider 1% to be the maximum then that is very close. That is before you consider the additional resistance of the terminations and fuses. Set the batteries to charge for an hour or so and get an IR thermometer or thermal camera on the cables/terminations. They'll be plenty toasty!

Using two sets of cables to connect both ends of the batteries the the Switch fuse disconnect would improve the situation a lot, as would using a bigger cable from the disconnect to the inverter. In resrospect you're probably fone with NH00 which is rated to 160A so is fine for 105(ish)A. NH1 is rated for 250A...

[pudding]

Oh yes, I've felt the cables when at full tilt and they're warm!

I'll get 2 sets of 35mm cables, ready for the upgrade to 2x Diy Seplos Mason kits too. Now, diy cables and new crimping tools, or are there ready made 35mm cables to use? Guess I'll need a crimping tool though for a 70mm cable from disconnect to inverter so may as well diy the lot and all connectors.

[Saladin]

I'm a fan of oversizing cables so I'd go 35mm² for 100A.
25mm² is adequate if it's genuine cable, and not all of it is. Funny thing I've noticed on boats is 10 year old 35mm² cable doen't fit into modern 35mm² lugs...but modern 35mm² cable does (actually 30mm² referencing the specific one I'm talking about, with 35mm² printed on the insulation).

Nothing wrong with warm cables as long as it's below 60°C at full load or higher for heat resistant cables. It's one of those compromise things, you factor it in. It's quite an undertaking to build anything over 300A without heat soaking hysteresis. Day one isn't cabling it's metal fabrication!

I over-spec for overhead, upgradeability, unforgiving voltage drop issues like using engine alternators to charge leady house batteries on liveaboards, for thermal wicking of fuseholders, mechanical resilience, to prevent conducting heat into other components like inverter FETs and motherboards.

I've seen plenty commercial installations running 90°C cables in silicon jackets because the losses are subsidised by the clients and workers but the installation wasn't.

[Stinsy]

I'm a fan of oversizing cables so I'd go 35mm² for 100A.
25mm² is adequate if it's genuine cable, and not all of it is. Funny thing I've noticed on boats is 10 year old 35mm² cable doen't fit into modern 35mm² lugs...but modern 35mm² cable does (actually 30mm² referencing the specific one I'm talking about, with 35mm² printed on the insulation).

Nothing wrong with warm cables as long as it's below 60°C at full load or higher for heat resistant cables. It's one of those compromise things, you factor it in. It's quite an undertaking to build anything over 300A without heat soaking hysteresis. Day one isn't cabling it's metal fabrication!

I over-spec for overhead, upgradeability, unforgiving voltage drop issues like using engine alternators to charge leady house batteries on liveaboards, for thermal wicking of fuseholders, mechanical resilience, to prevent conducting heat into other components like inverter FETs and motherboards.

I've seen plenty commercial installations running 90°C cables in silicon jackets because the losses are subsidised by the clients and workers but the installation wasn't.

+1 for going up a size and also for cable fraud being widespread!

I'm seeing a lot more battery packs and inverters in the 80-480V range. If you're charging/discharging much faster than 100A then this seems very sensible.

[Joeboy]

If its of use to anyone. I have bought a couple of times from an ebay seller 'split charge' being their shop name. Good quality cables, many sizes.

https://www.ebay.co.uk/itm/201702388802

[pudding]

Excellent, love the suggested retailers etc. I'm thinking of going for 50mm cable from inverter to disconnector/connector block, so I can use a crimping tool that goes up to 50mm cable (Seems to jump in price if you need more for example 70mm cable). Any suggestions for these, or will any cheap crimping tool such as this do - https://www.amazon.co.uk/Electrician-Re ... rce=1&th=1 or hydraulic - https://www.ebay.co.uk/itm/365165203632 ... B300390417&

[Stinsy]

Excellent, love the suggested retailers etc. I'm thinking of going for 50mm cable from inverter to disconnector/connector block, so I can use a crimping tool that goes up to 50mm cable (Seems to jump in price if you need more for example 70mm cable). Any suggestions for these, or will any cheap crimping tool such as this do - https://www.amazon.co.uk/Electrician-Re ... rce=1&th=1 or hydraulic - https://www.ebay.co.uk/itm/365165203632 ... B300390417&

Crimping tools aren't sophisticated. The expensive ones will last longer if you're doing hundreds and might be more enjoyable to use. But physics is physics, so long as the handles are long enough and the ,ug passes the pull test, you're golden.