Input from solar panels

Submitted: Monday, Oct 20, 2014 at 11:47
ThreadID: 109871 Views:1895 Replies:4 FollowUps:10
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How many volts should be going into a vehicle battery from a 140 w panel in full sunlight through a MPPT controller? I'm seeing low 13s which I suspect is not enough. Should I be getting closer to 14?
Thanks in advance.
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Reply By: Gronk - Monday, Oct 20, 2014 at 12:18

Monday, Oct 20, 2014 at 12:18
Depends on the state of charge of the battery...

It may start off with low 13's, but then slowly climb to low or even mid 14's, then settle around 13.7 when the battery is fully charged ( float voltage ).

These figures are an AGM battery, but depends on if you have AGM or wet cell batteries and if you have/can adjust the controller to suit..

AnswerID: 540586

Follow Up By: Krooznalong - Monday, Oct 20, 2014 at 12:24

Monday, Oct 20, 2014 at 12:24
Thanks Gronk
Battery would have been close to fully charged - driving most of previous day so had only run the fridge overnight and it was a cool night so it wouldn't have had to do too much work.

Battery is a normal lead acid - not AGM.

Controller is not adjustable - it's the one that came attached to the ebay panels so undoubtedly a cheapie.

I have never seen anything more than low 13s so I suspect a better quality MPPT controller is required.
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Follow Up By: garrycol - Monday, Oct 20, 2014 at 12:42

Monday, Oct 20, 2014 at 12:42
Krooznalong - sounds all normal to me for a battery that is near fully charged.
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Follow Up By: Nomadic Navara - Monday, Oct 20, 2014 at 13:59

Monday, Oct 20, 2014 at 13:59
Disconnect the panel after the days charge. Reconnect it mid morning the next day (or get someone else to connect it) whilst you are watching the volt meter. The meter should slowly rise to over 14 V, stay there for some time and then drop back to the float voltage. If you reconnect the panel with a fully charged battery it can go through that voltage cycle in less than 30 seconds so you have to watch the meter whilst reconnecting.


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Reply By: Bob Y. - Qld - Monday, Oct 20, 2014 at 15:22

Monday, Oct 20, 2014 at 15:22
Krooz,

Have a 160w panel permanently fixed to my slide-on camper, running through a Redarc BMS to 2 x 120 amphr batteries. The readout of the BMS often tells me I have 19-20 volts solar output, and 13-14 volts going into the battery, so yours sounds okay to me.

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Follow Up By: Krooznalong - Monday, Oct 20, 2014 at 15:41

Monday, Oct 20, 2014 at 15:41
Thanks Bob and others
Still concerned because I've never seen anywhere near 14v. 13.2 is about the highest I ever recall seeing and I think that's too low. To charge properly I believe it needs the same as the alternator which usually sits a bit above 14v until it is fully charged and then drops back to mid/high 13s.
Might have to do some testing on the weekend (hopefully the sun will be shining!).
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Follow Up By: B1B2 - Monday, Oct 20, 2014 at 17:46

Monday, Oct 20, 2014 at 17:46
Krooza,
Disconnect your battery and check the output voltage from the solar panels. It should be around 17 vdc. That will prove the panels are good.


Cheers,

Bill
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Follow Up By: Krooznalong - Tuesday, Oct 21, 2014 at 08:36

Tuesday, Oct 21, 2014 at 08:36
Bill - I know the panels are good. Tested them some time ago. I suspect the controller. More testing to be done.
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Reply By: patsproule - Monday, Oct 20, 2014 at 19:29

Monday, Oct 20, 2014 at 19:29
Unglue the controller from the back of the panels and mount it up near the battery. This will avoid the voltage drop over the feed cable.
AnswerID: 540597

Follow Up By: Gronk - Monday, Oct 20, 2014 at 21:55

Monday, Oct 20, 2014 at 21:55
Yep, how long is the lead from the panel to the battery ?
How big is the cable ?

If the controller is putting out 14 + volts and you have 1 volt voltage drop, then there is your problem. Even 1/2 a volt is too much, which is why it's always a good idea to have the controller as close to the batt as possible.
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Follow Up By: Krooznalong - Tuesday, Oct 21, 2014 at 08:39

Tuesday, Oct 21, 2014 at 08:39
I already have the controller near the battery. So I'm dubious about the controller. Will be doing some testing over the weekend to see if it is the problem.
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Follow Up By: willys701926 - Tuesday, Oct 21, 2014 at 11:28

Tuesday, Oct 21, 2014 at 11:28
Is you MPPT adjustable? With mine you can set voltage levels for bulk and float charge states
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Follow Up By: Garry S3 - Tuesday, Oct 21, 2014 at 21:47

Tuesday, Oct 21, 2014 at 21:47
it sounds like a voltage drop more than anything. one way to check it is to check at the output point on the solar regulator. it might be doing something like 14v but through the cable, reduce to 13
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Reply By: Travelling - Wednesday, Oct 22, 2014 at 16:26

Wednesday, Oct 22, 2014 at 16:26
An MPPT controller that WORKS correctly will cost you more than $200
Haven't yet tested an MPPT controller under $200 that works as well as a good PWM regulator. They lock onto the wrong part of the curve and then stay at the incorrect point and don't resample the curve.
The regulator on the back of the panels is useless. The regulator needs to be within 1M of the battery with correct size wire and correct size wire from solar panel to regulator.
This is the cheapest MPPT solar regulator that functions as described
http://www.morningstarcorp.com/products/sunsaver-mppt/
and MPPT solar regulators from there go up on price.
AnswerID: 540687

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