Hank the Tanks Dodgy battery and solar system

barryd said:
This is how I understood it should work up thread. The first one is wrong as it will cause the first battery to discharge quicker I think and the second one will try and then charge the first one. I think you have to wire the positive feed to one battery and then the negative to the other to in effect create one battery from the two and you need to do the same with anything that is connected to it so the positive of say a 12v socket goes to one battery but the negative goes to the other. What I need to know is what cables are required for connecting the two batteries inbetween. I think I have this right but my heads a bit fuzzy this morning.

View attachment 141040
View attachment 141041
Click to expand...
With 2 batteries it honestly really won't make that much difference .

Cable wise ....you want some nice chunky cable

This is what I've used

Screenshot_20250314_092603_Chrome.jpg
 
barryd said:
This is how I understood it should work up thread. The first one is wrong as it will cause the first battery to discharge quicker I think and the second one will try and then charge the first one. I think you have to wire the positive feed to one battery and then the negative to the other to in effect create one battery from the two and you need to do the same with anything that is connected to it so the positive of say a 12v socket goes to one battery but the negative goes to the other. What I need to know is what cables are required for connecting the two batteries inbetween. I think I have this right but my heads a bit fuzzy this morning.

View attachment 141040
View attachment 141041
Click to expand...

OK Barry the second diagram is the preferred method. You simply "join" both pos and neg terminals together but take the pos feed from battery B but make sure the neg feed comes from batt A.


Simples
 
mistericeman said:
With 2 batteries it honestly really won't make that much difference .

Cable wise ....you want some nice chunky cable

This is what I've used

View attachment 141043
Click to expand...

Thanks. I assumed we would get something ready made up but I am not sure what connections we need at both ends now after chatting with Merl yesterday. I need to compile a list of exactly what needs to be ordered and from where.
 
barryd said:
Thanks. I assumed we would get something ready made up but I am not sure what connections we need at both ends now after chatting with Merl yesterday. I need to compile a list of exactly what needs to be ordered and from where.
Click to expand...
The ends you need will I'd guess depend on what battery clamps you already have and which ones you buy for the new batteries .
 
mistericeman said:
I meant more the attachments for the cables ...

I used these

View attachment 141045

BUT they do need attaching to the cables ...soldering/crimping

Then connected them to the clamping bolts on the actual battery clamps ....as the clamps I used didn't have busbars on them .
Click to expand...
Absolutely, none of the screw on types posted before.

I have these arriving today to replace the manky ones I have on the LB.

 
barryd said:
It will be two of these. Identical.

View attachment 141044


From the link above. Looks like the positive is slightly larger than the negative.

Terminal LayoutPositive on Right (Layout 0)
Terminal TypeStandard Round (Type 1)

View attachment 141046
View attachment 141047
Click to expand...
Maybe get two sets of the same types as this Barry, easy to work with and the clamps stay fastened.

 
barryd said:
This is how I understood it should work up thread. The first one is wrong as it will cause the first battery to discharge quicker I think and the second one will try and then charge the first one. I think you have to wire the positive feed to one battery and then the negative to the other to in effect create one battery from the two and you need to do the same with anything that is connected to it so the positive of say a 12v socket goes to one battery but the negative goes to the other. What I need to know is what cables are required for connecting the two batteries inbetween. I think I have this right but my heads a bit fuzzy this morning.

View attachment 141040
View attachment 141041
Click to expand...
Technically the link cables only need to be 50% of the capacity of the main feed, ( because they'll be carrying 50% of the total current) . Your main feed looks like 10mm so anything over a paltry 5mm will suffice. What we go for will depend on how much future proofing you want to build in, we can discuss that.....along with quite a lot more.
Biggest issue is cable size between solar controller and batteries, looks like you've currently got about 3m of 1.5mm flex. At full sun this cable will be dropping approx 1/2 a volt so when the controller thinks your battery is full and reduces its charge current because it senses 14.6 volts the actual battery will only be at 14.1v and way under charged, this (IMO) is why you seem to be able to recharge the leisure battery very quickly and why you don't seem to have a lot of useable capacity.
We should consider moving the controller closer to the batteries and/or upping the cable gauge between SCC and batteries.
As I've expressed previously (way back in this thread) you should consider a mppt controller, either get a Votronic with a maintenance output to the starter battery or a single output mppt and I'll make you up a 'little Gizmo' that'll fit between the leisure and starter battery and keep the starter maintained, it's basically like the Ablemail, Stirling etc battery maintainers but better and cheaper. I've got one fitted to my van and it works like a charm. (I'm going to post details of this device soon for anyone interested)
I think the best thing you and I can do is have a discussion about your usage (current and projected) and devise a plan and at that point ( if you feel a need to get qualification before proceeding) post details here so anyone with an opinion can chip in. We then alter/modify the plan if needed and then get the job done.
 
merl said:
Technically the link cables only need to be 50% of the capacity of the main feed, ( because they'll be carrying 50% of the total current) . Your main feed looks like 10mm so anything over a paltry 5mm will suffice. What we go for will depend on how much future proofing you want to build in, we can discuss that.....along with quite a lot more.
Biggest issue is cable size between solar controller and batteries, looks like you've currently got about 3m of 1.5mm flex. At full sun this cable will be dropping approx 1/2 a volt so when the controller thinks your battery is full and reduces its charge current because it senses 14.6 volts the actual battery will only be at 14.1v and way under charged, this (IMO) is why you seem to be able to recharge the leisure battery very quickly and why you don't seem to have a lot of useable capacity.
We should consider moving the controller closer to the batteries and/or upping the cable gauge between SCC and batteries.
As I've expressed previously (way back in this thread) you should consider a mppt controller, either get a Votronic with a maintenance output to the starter battery or a single output mppt and I'll make you up a 'little Gizmo' that'll fit between the leisure and starter battery and keep the starter maintained, it's basically like the Ablemail, Stirling etc battery maintainers but better and cheaper. I've got one fitted to my van and it works like a charm. (I'm going to post details of this device soon for anyone interested)
I think the best thing you and I can do is have a discussion about your usage (current and projected) and devise a plan and at that point ( if you feel a need to get qualification before proceeding) post details here so anyone with an opinion can chip in. We then alter/modify the plan if needed and then get the job done.
Click to expand...
That sounds like a good plan Merl
 
Geek said:
Not incorrect at all.
The first battery gets the full output, the second just gets a trickle. You say 1 amp, which sounds about right.
Which bank is the first is down to the installation, but they do NOT both get MPPT charging.
I do have one of these units, and although I don't use it, I have tested it.
Click to expand...
You have wired it up incorrect, the high feed goes to as many batteries as you like for hab, the small output goes to the starter batt, i have a city & gills in electronics so i have a good notion what im talking about.
start.jpg
 
merl said:
Technically the link cables only need to be 50% of the capacity of the main feed, ( because they'll be carrying 50% of the total current) . Your main feed looks like 10mm so anything over a paltry 5mm will suffice. What we go for will depend on how much future proofing you want to build in, we can discuss that.....along with quite a lot more.
Biggest issue is cable size between solar controller and batteries, looks like you've currently got about 3m of 1.5mm flex. At full sun this cable will be dropping approx 1/2 a volt so when the controller thinks your battery is full and reduces its charge current because it senses 14.6 volts the actual battery will only be at 14.1v and way under charged, this (IMO) is why you seem to be able to recharge the leisure battery very quickly and why you don't seem to have a lot of useable capacity.
We should consider moving the controller closer to the batteries and/or upping the cable gauge between SCC and batteries.
As I've expressed previously (way back in this thread) you should consider a mppt controller, either get a Votronic with a maintenance output to the starter battery or a single output mppt and I'll make you up a 'little Gizmo' that'll fit between the leisure and starter battery and keep the starter maintained, it's basically like the Ablemail, Stirling etc battery maintainers but better and cheaper. I've got one fitted to my van and it works like a charm. (I'm going to post details of this device soon for anyone interested)
I think the best thing you and I can do is have a discussion about your usage (current and projected) and devise a plan and at that point ( if you feel a need to get qualification before proceeding) post details here so anyone with an opinion can chip in. We then alter/modify the plan if needed and then get the job done.
Click to expand...

Thanks very much Merl. I am more than happy to be guided by you. Totally agree about the cabling. I was never happy with that. Not averse to changing the controller either or how the engine battery is topped up. Lets have a chat over the weekend maybe. Ill see if I can get measured up on the roof as well.

I always liked my old MPPT Controller as it displayed all the voltages / watts going in and out on an LCD screen. Old hat now I would imagine and as suggested its probably best to have something thats future proof for Lithium.

This was my old one.

MPP Solar Inc » PCM2012/3012 Series

www.mppsolar.com www.mppsolar.com
 
Last edited:
You must log in or register to reply here.

Users who viewed this discussion (Total:52)

Back
Top