100W solar panel

wildebus

Full Member

Messages
3,745
How close do the specs have to be? Does it have to be an exact match? Is it the open circuit voltage we need to look at?
Basically, when you connect multiple panels in Series , you add the voltages together, and the amperage is the lowest of any of the panels.
If wired in Parallel, you add the amperages, but the voltage is the lowest of any of the panels.

Give you an example from a pair of panels from Photonic Universe ....

80W Panel - Max Voltage = 20.2V; Max Current = 3.96A
100W Panel - Max Voltage = 20.2V; Max Current = 4.95A

If you wired up in Parallel, you would get the full 180W potential, but in Series, the 100W Panel is limited to 80W maximum. In this case the Panels are from the same range so have a common factor and can be configured optimally.

If I used a 100W Renogy Panel instead, that has a Voltage of 17.9V and Current of 5.72A. Add this to the 80W Panel above, you would have:
in Series: Voltage of 38.1V & Current of 3.96A = 151W
in Parallel: Voltage of 17.9V & Current of 9.68A = 173W
Here, you cannot get the full benefit either way of the extra 100W panel, but parallel will give you the best possible result. If you happened to add a 24V panel to an existing 12V panel, you would never wire in parallel as you would instantly halve the 24V Panels output.

End of the day, if you know the spec of the panel fitted, you can try to find the best matched option to add in.


(corrected: had Series and Parallel swapped!)
 
Last edited:

Full Member

Full Member

Messages
4,587
Basically, when you connect multiple panels in Parallel, you add the voltages together, and the amperage is the lowest of any of the panels.
If wired in Series, you add the amperages, but the voltage is the lowest of any of the panels.

Give you an example from a pair of panels from Photonic Universe ....

80W Panel - Max Voltage = 20.2V; Max Current = 3.96A
100W Panel - Max Voltage = 20.2V; Max Current = 4.95A

If you wired up in Series, you would get the full 180W potential, but in Parallel, the 100W Panel is limited to 80W maximum. In this case the Panels are from the same range so have a common factor and can be configured optimally.

If I used a 100W Renogy Panel instead, that has a Voltage of 17.9V and Current of 5.72A. Add this to the 80W Panel above, you would have:
in Parallel: Voltage of 38.1V & Current of 3.96A = 151W
in Series: Voltage of 17.9V & Current of 9.68A = 173W
Here, you cannot get the full benefit either way of the extra 100W panel, but series will give you the best possible result. If you happened to add a 24V panel to an existing 12V panel, you would never wire in series as you would instantly halve the 24V Panels output.

End of the day, if you know the spec of the panel fitted, you can try to find the best matched option to add in.

Dave- you may wish to revisit sentences 1 and 2 et cetera.

Colin :):):)
 
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TrevandJenny

Full Member

Messages
74
Thanks to you all for the above, Molly 3 hits the nail on the head, My system is as Mollys, ref 120 watts input, my panel 80 watts I can see the need to change controller ect to obtain the max on roof, 2 x 120w panels could fit, together with suitable MPPT controller,
.
I have got my head round it now, thanks. Just a thought though, can I still use the sargent 240v system to charge my batteries when on leccy hook up???? Will the alternator still charge the leisure batteries with the new MPPT controller when fitted???

Thanks again.:):)
 

wildebus

Full Member

Messages
3,745
Thanks to you all for the above, Molly 3 hits the nail on the head, My system is as Mollys, ref 120 watts input, my panel 80 watts I can see the need to change controller ect to obtain the max on roof, 2 x 120w panels could fit, together with suitable MPPT controller,
.
I have got my head round it now, thanks. Just a thought though, can I still use the sargent 240v system to charge my batteries when on leccy hook up???? Will the alternator still charge the leisure batteries with the new MPPT controller when fitted???

Thanks again.:):)
There are a couple of Sargent systems that apparently will charge Leisure and Starter Batteries at the same time. I am not sure which models they are. Most of them, including mine (I have an EC325) will charge whichever battery is selected on the Control Panel - e.g. Leisure OR Vehicle (but no both).

Changing the Solar Control should have no effect on how either the Mains Charger or the Split (alternator) charger operates.
 

trevskoda

Full Member

Messages
2,087
I would take in what wildbus is telling you, I did and done some upgrades to my sys with a votronic unit, now as happy as a pig in s-it.solar duel a.png
 

Markd

Full Member

Messages
1,078
That's a good price for 250w controller not much more than I paid for my 165w 😀
I wish I'd got this capacity to allow me to double up my solar panel.
 

TrevandJenny

Full Member

Messages
74
I must be missing something here, correct me if I am wrong. By fitting a upgraded controller I assume that the wiring from the Sargent system is disconnected and new wiring installed from panel to controller to batteries.
.
If this is the case how does the alternator and hookup work unless original wiring is split.
.
When we purchased our MH on handover the salesman advised that the solar system will always charge the engine battery to max then change over to leisure battery, I now doubt his advice.
 

wildebus

Full Member

Messages
3,745
I must be missing something here, correct me if I am wrong. By fitting a upgraded controller I assume that the wiring from the Sargent system is disconnected and new wiring installed from panel to controller to batteries.
.
If this is the case how does the alternator and hookup work unless original wiring is split.
.
When we purchased our MH on handover the salesman advised that the solar system will always charge the engine battery to max then change over to leisure battery, I now doubt his advice.
The only thing you are disconnecting from the Sargent unit is the connection between it and the solar panel. That has no impact on anything else. It will like the Sargent is not aware of any solar being installed.

You have not told us what model of Sargent unit you have in your Autosleeper, so can't be sure if what you have been told is correct or not, but my suspicion is it was not correct. It sounds at best that he got the batteries round the wrong way, but I think he was just plain wrong.
 

Markd

Full Member

Messages
1,078
When we purchased our MH on handover the salesman advised that the solar system will always charge the engine battery to max then change over to leisure battery, I now doubt his advice.
Personally I'd set any solar dual charger the other way round prioritising Leisure Batteries.
However I can see the argument that if the starter battery is full you can at least run the engine to charge the Leisure battery.

I tend to agree with Wildebus about the Sargent charger being sequential - it's my understanding that it does one or the other depending on which battery you've selected to run habitation electrics.
 

TrevandJenny

Full Member

Messages
74
MH back home, Sargent charger is a 328 model, Specs in MH booklet says max 120W panel and will charge the engine and leisure batteries ,
.
I am now of the mind to retain the Sargent system and replace the 80w panel with a 120w panel to see the outcome, now with the advice and statistics given as above it seems a good option, if it does not go as well as I hoped I can then refit the original 80W panel together with the 120w panel and a MPPT controller, that would give me 200w. Then when my pair of AGM batteries fail I could replace with lithium. Hopefully job done.
.
Unless the teckky ones on the forum think its not a good way to go.

Thanks for all the advice given so far.
 

Markd

Full Member

Messages
1,078
Glad to hear that E328 does both sets on a needs based priority. I'm happy to eat humble pie on that.
I have read on a website that I can't link to from here that Sargent Solar controllers are far from the best and if your leisure battery is more than a metre or two from it the voltage drop will significantly reduce performance.
If you have the inclination and time it might be I treating to measure the voltage at the battery when it's being bulk charged.
On my motorhome the cable length was 5m and only 4mm² - when I put in my Votronic I cut the connection length to 1m with 6mm². Votronic also claim that their chargers compensate for any voltage drop by measuring battery voltage between charge pulses.
Hang onto your 80w panel in case you don't get the performance you want and you can add it to the 120w and hook them up to a Votronic - with 2 AGM leisure batteries you're far more likely to get them fully recharged in one day of solar.
 
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Geek

Full Member

Messages
42
I have never seen an MPPT controller that properly charges two lots of batteries. Not saying there aren't any, but I've not seen one.
The Votronic unit is a good MPPT charger that does multistage charging to the leisure bank, but just provides a trickle charge to the starter battery.
If that isn't good enough, you'd be well advised to find the fault that's draining the starter battery rather than look for a different charge controller.
 

Geek

Full Member

Messages
42
Hang onto your 80w panel in case you don't get the performance you want and you can add it to the 120w and hook them up to a Votronic - with 2 AGM leisure batteries your far more likely to get them fully recharged in one day of solar.
Maybe. I've tried connecting two solar panels using two MPPT controllers to the same battery bank.
Each time, as soon as I connected the second controller, they both stopped working. Even though worth of them works with mains or alternator charge going in.
I've no idea why. Perhaps it will work for you, but it didn't for me.
 

wildebus

Full Member

Messages
3,745
Maybe. I've tried connecting two solar panels using two MPPT controllers to the same battery bank.
Each time, as soon as I connected the second controller, they both stopped working. Even though worth of them works with mains or alternator charge going in.
I've no idea why. Perhaps it will work for you, but it didn't for me.
If I am reading this correctly, you have been unable to run more than one Solar Controller (and maybe specifically MPPT Controllers?) on single Battery Bank?
That is certainly not a common problem. I have not actually heard of anyone having that issue before.
 

Geek

Full Member

Messages
42
Connecting them was no trouble. They just didn't work!
As I said, no idea why not.
It didn't matter which order I connected them, when the second one was connected, the first one stopped charging within a few seconds. Seemed very odd to me.
 

Markd

Full Member

Messages
1,078
Perhaps because they each sensed the 'high' voltage from the other and concluded that the battery was charged so 'shut' down?
 

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