Idiot's guide to a self build battery

[nowty]

I'll be using 20mm cable for battery interconnects that I can't do with the supplied busbars, which should be good for 135A. And a set of long pylontech cables to branch off the Pylon stack. So to protect the cables 100A fuses should be good I think. I reckon I could go lower as during normal operation once balanced I'd expect no more than about 10 - 20A as the LF280s will share the work with all 6 Pylons.

Whatever the spec says, halve it, 135A on a 20m㎡ cable ?

100A on a 25m㎡ Pylontech cable is very warm, 120A on 25m㎡ Pylontech cable is very hot. There are some thinwall cables capable of higher temps but do you want cables which are potentially too hot to touch ?

I sometimes go to 166A on my 70m㎡ cable back to the inverter and its warm. And hot where it goes through an isolator or fuse block even with bolt down ceramic fuses with extra copper here and there for both conductivity and heatsinking.

This is what I used to have, within spec for 120A or more but it was too hot for comfort at around 120A, even with 35m㎡ intermediate cables.



Now with more copper and 50m㎡ intermediate cables, much more comfortable, still gets warm though at 120A. The bottom left cable is only 25m㎡ because it comes from my Victron charge controller and supplementary battery charger limited to around 40A max.

[Joeboy]

I'll be using 20mm cable for battery interconnects that I can't do with the supplied busbars, which should be good for 135A. And a set of long pylontech cables to branch off the Pylon stack. So to protect the cables 100A fuses should be good I think. I reckon I could go lower as during normal operation once balanced I'd expect no more than about 10 - 20A as the LF280s will share the work with all 6 Pylons.

Whatever the spec says, halve it, 135A on a 20m㎡ cable ?

100A on a 25m㎡ Pylontech cable is very warm, 120A on 25m㎡ Pylontech cable is very hot. There are some thinwall cables capable of higher temps but do you want cables which are potentially too hot to touch ?

I sometimes go to 166A on my 70m㎡ cable back to the inverter and its warm. And hot where it goes through an isolator or fuse block even with bolt down ceramic fuses with extra copper here and there for both conductivity and heatsinking.

This is what I used to have, within spec for 120A or more but it was too hot for comfort at around 120A, even with 35m㎡ intermediate cables.



Now with more copper and 50m㎡ intermediate cables, much more comfortable, still gets warm though at 120A. The bottom left cable is only 25m㎡ because it comes from my Victron charge controller and supplementary battery charger limited to around 40A max.

That's all great to read Nowty, looking forward to seeing it next week on our return. I'll be buying myself an ampclamp too as going this far it would me mad not to have that flow info readily to hand. If its OK I will ask you about the benefits if any of fusing each of the three banks of 5 batteries even though they are in series. Seems logical as fault within one battery will hopefully blow the fuses on each end of the 5 bank and not melt any other assets (cables) or stress the other batteries?

It seems strange to me that the max load the LF280's will see in normal operation is during charging. The discharge side is relatively low due to inverter restrictions. Again, I may be stating the obvious but it's all new to me as was the thought of the figure C yesterday as a handle on discharge rate and heat.

I am also just becoming aware that my Victron set up has the potential to be putting out a fair skite of power unrestricted on its own. 4,800kW max at 115v to the charge controller is 41.7A. I am looking forward to seeing what the amp clamp figure is from the charge controller to the Pylontechs in reality.

[Stinsy]

That's all great to read Nowty, looking forward to seeing it next week on our return. I'll be buying myself an ampclamp too as going this far it would me mad not to have that flow info readily to hand. If its OK I will ask you about the benefits if any of fusing each of the three banks of 5 batteries even though they are in series. Seems logical as fault within one battery will hopefully blow the fuses on each end of the 5 bank and not melt any other assets (cables)?

It seems strange to me that the max load the LF280's will see in normal operation is during charging. The discharge side is relatively low due to inverter restrictions. Again, I may be stating the obvious but it's all new to me as was the thought of the figure C yesterday as a handle on discharge.

It is generally external factors you are insuring against with a fuse. Your Pylontechs have inbuilt overcurrent/short-circuit protection but your new batteries don’t. Therefore a metal tool used negligently, or other mishap, could cause a short drawing thousands of amps. This would damage the batteries and could be unpleasant for nearby humans. A cheap fuse close to the battery pack would be a good precaution.

[Joeboy]

That's all great to read Nowty, looking forward to seeing it next week on our return. I'll be buying myself an ampclamp too as going this far it would me mad not to have that flow info readily to hand. If its OK I will ask you about the benefits if any of fusing each of the three banks of 5 batteries even though they are in series. Seems logical as fault within one battery will hopefully blow the fuses on each end of the 5 bank and not melt any other assets (cables)?

It seems strange to me that the max load the LF280's will see in normal operation is during charging. The discharge side is relatively low due to inverter restrictions. Again, I may be stating the obvious but it's all new to me as was the thought of the figure C yesterday as a handle on discharge.

It is generally external factors you are insuring against with a fuse. Your Pylontechs have inbuilt overcurrent/short-circuit protection but your new batteries don’t. Therefore a metal tool used negligently, or other mishap, could cause a short drawing thousands of amps. This would damage the batteries and could be unpleasant for nearby humans. A cheap fuse close to the battery pack would be a good precaution.

Sounds good to me, I will be seeking help on the fuse spec and positioning. I would like to be able to tag a fuse onto each end of each bank of 5 batteries, preferably straight onto the incoming and outgoing terminal then link all in series? I can't though can I? As the new bank is all in series. Do I instead fuse both ends of the entire15 bank and forget about protecting each bank of 5 as well? I don't want to install blocks to flow unless they serve a good purpose?

I thought this wee unit would be enough for my simple DIY needs?
https://www.ebay.co.uk/itm/393983757199 ... %7Ciid%3A1

[billi]

I thought this wee unit would be enough for my simple DIY needs?
https://www.ebay.co.uk/itm/393983757199 ... %7Ciid%3A1

Better get one , that meters DC- current too

[Caesium]

I have this one which I can recommend, does DC and AC current up to 100A https://www.ebay.co.uk/itm/384965746593

[Joeboy]

I have this one which I can recommend, does DC and AC current up to 100A https://www.ebay.co.uk/itm/384965746593

That's actually hilarious. I would go and buy a meter that won't do AC & DC as a current clamp . Well, as the title says...
Luckily I've not bought yet!

[marshman]

__

[Joeboy]

I have this one which I can recommend, does DC and AC current up to 100A https://www.ebay.co.uk/itm/384965746593

That's actually hilarious. I would go and buy a meter that won't do AC & DC as a current clamp . Well, as the title says...
Luckily I've not bought yet!

So easy to do on eBay, the product title is deliberately misleading in my opinion, but the real indicator is the price. "non invasive" DC measurement is harder than AC, AC "just" needs a current transformer, most DC clamps need to use a hall effect device.

The UNI-T one linked to by Caesium is the one I have and I can recommend it as well, not that accurate at low DC levels (<1 A) but otherwise OK.

Thank you Marshman and all of you! Never overestimate my knowledge or indeed skill in these sparky things!

[Oldgreybeard]

The give away, as well as the often dodgy description, is whether there is a zero button usually. Those with no zero button don't usually measure DC current, those with usually do. These cheap meters drift off zero when measuring DC current a fair bit, hence the need to zero the current reading every time it's used.