Extra solar power...or not.

[slocumjoseph]

I have a newly installed 200w solar system to dual charge my batteries through a Renogy DC-DC charger and MPPT controller. I still have my old 100w portable panel and thought if I ever needed the extra PV power I could just plug it directly onto the leisure battery like I used to do. However I have a couple of cracks in my confidence and need a bit of expert reassurance…or otherwise before I add it. It has a PWM controller and plugs directly on to the leisure battery with crocodile clips. Hopefully there is no conflict between the PWM and MPPT controllers as although connected to the same battery they are independent of each other. The output from the panel on the pop top is 23.9v so within the Renogy controllers maximum of 25volts but I’m hoping that if I plug the portable panel directly into the leisure battery while the one on the roof is still connected nothing will get fried. In other words, can I have both systems on at the same time?

 

[Pete C]

It should work fine, as each controller will sense the battery voltage and do what it thinks appropriate. The geek in me would be interested to see how they interact with each other in sunny weather.

Pete

 

[Nigel W]

Thinking about this my leisure battery has charging from MPPT, B2B, mains hook up charger and for good measure because the converter didn’t know better a split charge device.
so when driving it has 3 things charging it and when on hook up 2.
I guess they all sort things out between them?

 

[t0mb0]

Thinking about this my leisure battery has charging from MPPT, B2B, mains hook up charger and for good measure because the converter didn’t know better a split charge device.
so when driving it has 3 things charging it and when on hook up 2.
I guess they all sort things out between them?

All of the actual chargers should interact fine. Having a split charge relay in there too could be very odd though, when the relay is closed, it’ll connect the batteries and therefore short the input/output of the B2B? If you really have got a relay and a B2B active at the same time then I would assume your B2B isn’t doing anything at all?

 

[Nigel W]

All of the actual chargers should interact fine. Having a split charge relay in there too could be very odd though, when the relay is closed, it’ll connect the batteries and therefore short the input/output of the B2B? If you really have got a relay and a B2B active at the same time then I would assume your B2B isn’t doing anything at all?

At the risk of going off topic, I have a Sargent unit which has a built in split charge and as an after thought the converter subsequently fitted a Sterling B2B (this was 5 years ago when this issue was all very new and misunderstood).
It seems to work OK and I must admit it has given me concerns over the years but the converter is still using this arrangement and says it is safe.

 

[t0mb0]

At the risk of going off topic, I have a Sargent unit which has a built in split charge and as an after thought the converter subsequently fitted a Sterling B2B (this was 5 years ago when this issue was all very new and misunderstood).
It seems to work OK and I must admit it has given me concerns over the years but the converter is still using this arrangement and says it is safe.

I’m not making any statement on safety, but I’m reasonably sure that if the split charge relay is active and therefore connecting the starter and leisure battery together, then any B2B can’t be working at the same time because it’s had its input and output connected together. It may well be that they disabled the split charge when installing the B2B though - that would be the obvious thing to do.

Simple way to test is to start it up and just measure the voltage at starter and leisure - if it’s always basically the same (give or take some cable losses), then your B2B isn’t doing anything.

 

[Nigel W]

I’m not making any statement on safety, but I’m reasonably sure that if the split charge relay is active and therefore connecting the starter and leisure battery together, then any B2B can’t be working at the same time because it’s had its input and output connected together. It may well be that they disabled the split charge when installing the B2B though - that would be the obvious thing to do.

Simple way to test is to start it up and just measure the voltage at starter and leisure - if it’s always basically the same (give or take some cable losses), then your B2B isn’t doing anything.

Hi, sorry I didn’t mean to imply that you thought it was unsafe, that was just my thoughts on having 3 separate devices charging the battery at the same time.
thinking this through a bit more and looking at the battery connections I can see that the B2B is wired directly between the two batteries separately from the Sargent wires so they are both independent from each other.

 

[Salty Spuds]

I’m not making any statement on safety, but I’m reasonably sure that if the split charge relay is active and therefore connecting the starter and leisure battery together, then any B2B can’t be working at the same time because it’s had its input and output connected together. It may well be that they disabled the split charge when installing the B2B though - that would be the obvious thing to do.

Simple way to test is to start it up and just measure the voltage at starter and leisure - if it’s always basically the same (give or take some cable losses), then your B2B isn’t doing anything.

Maybe the split charge relay & the B2B are in series rather than parallel. I had this arrangement in my previous work T5. It had the factory 2nd battery & split charge relay. I took the output from the relay & fed it into the input of a Sterling 1230. The Sterling then fed the 2nd battery. Worked fine for the 5 years I had the van.

 

[t0mb0]

Maybe the split charge relay & the B2B are in series rather than parallel. I had this arrangement in my previous work T5. It had the factory 2nd battery & split charge relay. I took the output from the relay & fed it into the input of a Sterling 1230. The Sterling then fed the 2nd battery. Worked fine for the 5 years I had the van.

This is true, series would be fine. Hopefully it is.

Having said that, this might not be the case if the B2B is indeed wired directly between the batteries as a previous post says.

Easy to confirm by sticking a voltmeter over it.

 

[slocumjoseph]

Now there’s some interesting angles. Thanks for all the input. One of the things that prompted me to reorganise the charging system and add solar was the old split charge relay that was causing me big problems. Very little alternator charge got through to the leisure battery. So that was the first thing I removed from the system. As Renogys DC-DC charger and MPPT controller boasts it does it all. However, priorities have changed, the leisure battery is now kept topped up with the solar, even on dull days parked in the street but the SOC of the starter battery still slowly drops. It seems it does last longer without an alternator charge possibly because the controller is giving it a float charge. Of course as soon as I start the engine all charging goes straight to the engine battery. What I haven’t quite cottoned yet though is when/if the Renogy controller will eventually switch on a boost charge from the solar panel to the starter battery before it gets too low. Although without comprehensive monitoring it’s difficult for me to understand all the details of what’s going on.

Now I’ve just had another thought…my brain hurts!! What if put a permanent connection to the starter battery that I could use inside the cab. Then, if I left the portable solar panel on the top of the dash while I’m parked up in the street. Both batteries kept topped up without hot-wiring the lamp post!

 

[Nigel W]

I have a little solar panel on the dash which I just plug into the cig lighter which keeps the vehicle battery charged, no need to run any extra wires.

 

[prog99]

I’m not making any statement on safety, but I’m reasonably sure that if the split charge relay is active and therefore connecting the starter and leisure battery together, then any B2B can’t be working at the same time because it’s had its input and output connected together. It may well be that they disabled the split charge when installing the B2B though - that would be the obvious thing to do.

Simple way to test is to start it up and just measure the voltage at starter and leisure - if it’s always basically the same (give or take some cable losses), then your B2B isn’t doing anything.

Or simpler, look out for the lights on the sterling indicating the charger has kicked in.