Idiot's guide to a self build battery

[Joeboy]

Where is the air in coming from?

A hole

If it close to a 6" match I'd try what I said.

[Andy]

Where is the air in coming from?

A hole

If it close to a 6" match I'd try what I said.

Ah. The two big fans are doing what you say already. They are shifting hot air from the ceiling to outside to be replaced by cool(relatively) air from the outside. The trouble is I still got the temp gradient. It was only when I mixed the air from top to bottom that I was able to get rid of the temp gradient.

[Andy]

25mm is the same size as the standard pylontech cables, they get warm at 100A and hot at 120A. If your thinking of a continuous max over 100A I would be going to 35mm or even 50mm. I was shocked when you earlier mentioned “future proofing” at 25mm.

It’s not just the cables that generate heat, but the isolators, fuses, crimp connectors, etc.

I have 70mm cables to my main 8kW battery inverter and 50mm intermediates to each of my battery banks. I used to use 35mm for my intermediates but they got too warm for my liking if I was running only off a single bank at 150A so I upgraded to 50mm.

My loading per cable at the moment will be about 66A when I've finished the upgrade. It would go to 115A if I put in another 32 panels. In reality maybe 25A less if I'm constantly exporting 5kW. I've been having a nightmare trying to determine the cable size. The websites all have such widely varying stats. Do you have a go to reliable table based on max continuous usage? I have been leaning back to 35mm but will take your advice and go 50mm. I had 50mm installed on the 100A mppt and they barely get warm. Thanks for pointing out my mistake.

I've been trying to work out how things work with regards to heat. I have one 90mm or 100mm wire (I forget) which carries 9kW. The neutral which is uninterrupted is cool. The red one which goes through an isolator is always very warm. I can't see any extra hot spots at the lug crimps. Could the heat be travelling from inside the isolator? The wire also has got a tighter bend on it. Why would it be so much hotter. I'll try and get some photos when its running next time.

The pylontech are 21mm2 and good for 120A. I think they have a plastic coating that is rated for high temperatures. Even with only 4 sets they never seemed to feel warm while transferring about just below 300A between them.

[Joeboy]

A hole

If it close to a 6" match I'd try what I said.

Ah. The two big fans are doing what you say already. They are shifting hot air from the ceiling to outside to be replaced by cool(relatively) air from the outside. The trouble is I still got the temp gradient. It was only when I mixed the air from top to bottom that I was able to get rid of the temp gradient.

It's not quite the same. The cold air is being drawn in passively (albeit by expulsion of the two 6" fans). Thats not the same as forced cold air induction by a dedicated fan.

As to the heat in cables, could easy be resistance in an isolation switch, needs further investigation?

[Andy]

It's not quite the same. The cold air is being drawn in passively (albeit by expulsion of the two 6" fans). Thats not the same as forced cold air induction by a dedicated fan.

Ok, I'll try having reconfiguring the fans to an IN and an OUT and check out the difference. Will have to wait for a month or so as it's quite busy right now. Will keep you updated.

I do need to get the thermal camera on the inside of the isolator to see what's up. That's the only bit I haven't checked yet.

[Joeboy]

It's not quite the same. The cold air is being drawn in passively (albeit by expulsion of the two 6" fans). Thats not the same as forced cold air induction by a dedicated fan.

Ok, I'll try having reconfiguring the fans to an IN and an OUT and check out the difference. Will have to wait for a month or so as it's quite busy right now. Will keep you updated.

I do need to get the thermal camera on the inside of the isolator to see what's up. That's the only bit I haven't checked yet.

Think about setting up a positive crossflow. It does make a difference.

Discharge cables much the same length? For heat generation its traditionally a slack connection somewhere. .

[Andy]

It's not quite the same. The cold air is being drawn in passively (albeit by expulsion of the two 6" fans). Thats not the same as forced cold air induction by a dedicated fan.

Ok, I'll try having reconfiguring the fans to an IN and an OUT and check out the difference. Will have to wait for a month or so as it's quite busy right now. Will keep you updated.

I do need to get the thermal camera on the inside of the isolator to see what's up. That's the only bit I haven't checked yet.

Think about setting up a positive crossflow. It does make a difference.

Discharge cables much the same length? For heat generation its traditionally a slack connection somewhere. .

I got an insulated torque wrench on the way from ebay so I'll go and give them a tweak when it arrives. I think I might have offered too much as the seller accepted on the first go

[Stinsy]

Ok, I'll try having reconfiguring the fans to an IN and an OUT and check out the difference. Will have to wait for a month or so as it's quite busy right now. Will keep you updated.

I do need to get the thermal camera on the inside of the isolator to see what's up. That's the only bit I haven't checked yet.

Think about setting up a positive crossflow. It does make a difference.

Discharge cables much the same length? For heat generation its traditionally a slack connection somewhere. .

I got an insulated torque wrench on the way from ebay so I'll go and give them a tweak when it arrives. I think I might have offered too much as the seller accepted on the first go

A VDE torque wrench is very swish!

You can achieve something similar with insulating tape on your spanners.

However these batteries require a very high level of paying attention to what you’re doing. You’re working live with something that can deliver 1000A…

[Andy]

However these batteries require a very high level of paying attention to what you’re doing. You’re working live with something that can deliver 1000A…

Yes, it properly focusses the mind. I'll be isolating everything and even then wearing goggles in case I screw up. As someone said at work its worth working to a checklist.

[resybaby]

[/quote]

Hi, is something that they are happy to provide to people generally? I might be tempted myself if that’s the case
[/quote]

Robert, yes i think so. I just emailed them asking about the VAT removal and went from there - during our emails they offered the £50 'installation' VAT free idea.

Im collecting mine tomorrow, so will have a chat with them then if you want? and see if this is something they will do generally, will let you know what they say. I cant see they wouldnt as they were quite upfront with me and suggested it first.

Let me see what happens tomorrow and i'll report back on wednesday when im back home.