Solar panel charging conundrum

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simon501

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I have bought and installed a solara 45w panel and charge controller as an addition to my boat system.

The problem is this:

If I connect the solar charge controller output to the domestic battery bank (2 x 105Ah) the voltage at the controller for the battery connection is as at the battery (12.5V) as I would expect.

However, the voltage at the solar panel input is also 12.5V (not it's open voltage of 19V).

If I connect a 4.5Ah battery to the charge controller battery connection (instead of the domestic bank) the voltage is the same as the battery (as expected) BUT the voltage at the solar panel input stays at its open voltage of around 19V.

It appears (and this may be logical rubbish) that the small battery is being charged correctly but the larger batteries are not.

The charging lights on the controller seem to be correct with no indication of a problem.

The (BEP) battery monitor does not appear to show any charging when the solar is connected, but does if the shore power charger is on.

The battery system is the domestic bank plus a 85Ah starter battery and a VSR.

Can anybody help??

Thanks,

Simon
 
Simon, we have a Solar 45w panel and solar regulator, it trickles in about 13.7 - 13.9 volts permanently, well when the sun is shinning. Your 12.5v at the battery is the battery voltage not the solar panel, I don't think you panel is doing anything.

Pete
 
Controller units need to be attached to inputs and outputs in a specific sequence, which varies between makes.

Can you confirm that you have done this ?
 
Could be depending on the type of regulator. If it is a simple on/off regulator the output from the solar panel will be the same as the battery until the battery voltage gets to the cutoff voltage of the regulator.

Disconnect the solar panel from the regulator input to check the open circuit voltage of the solar panel.
 
Various observations/comments ... not in any particular order

Take note of what Sarabande says. If the instructions for the controller specify the order in which connections should made do as they say.

What is the controller

May be your large battery bank is not fully charged. It is still drawing current from the solar panel so its terminal volts have not had a chance to get up to 19.whatever.

BUT BUT BUT at 12.5 volts it is not charging anything not the small battery either.
I suspect your solar panel and or its controller may not be working at all.

Perhaps the BEP monitor is not registering the charge from the panel because you have the negative connected directly to the battery and the current is not going trough the shunt BUT more likely on reflection its because the solar panel system is not working!
 
The more current you are drawing from the panel, the lower the voltage will be.

What you are seeing, therefore, seems to be correct i.e. your main batteries are drawing a higher current so the voltage at the panel is lower, whereas the small battery is drawing little or no current so the voltage at the panel is close to or at open voltage.

It seems that you are expecting "charging" to be indicated by a high solar panel voltage, which is not the case.
 
What type of controller is it? Anything like "switching" or "MPPT" in the description?

The solar panel has an output characteristic that causes the voltage to drop as more current is taken from it. The controller is probably trying to take as much current as possible from the panel to charge the dirty great batteries you've connected to it and the panel voltage has fallen accordingly.
 
Wow - that was quick - many thanks!

Pete - That's what I think too, but only for the domestics. What's confusing me is the 4.5Ah battery I'm using to test the system appears to be being charged.

Sarabande - the make is Solara SR135TL - and the panel is Solara SM160M. According to the panel installation manual 'To prevent a short circuit, the cables to the battery should always be connected as the last ones, or removed as the first ones during any work on the module. So, battery first then solar array - seems to match up with the charge controller which is in interesting English!

Rogershaw - open voltage (at 1629) is 19.2V (Not connected to anything except the cell protector). Input side of the cell protector is also 19.2V. The user manual for the charge controller says it is a stage charge controller which include automatic adaptation to the ambient temperature.
 
Simon, we have the same Solara 15TL regulator, the connections on it are quite big to take HD wires, but even so we folded over the wire ends so they clamp properly.

I would ignore the little battery and go back and make all the connections again. Ensure as Vic says you wire the regulator to the right side of the battery.

Its going to be something simple like a poor connection. Test each of them with a separate volt meter.

Pete
 
Ensure as Vic says you wire the regulator to the right side of the battery.
Click to expand...
The right side of the shunt. The output from the regulator must pass through the shunt not go direct to the battery terminal. With a battery monitor there should be nothing directly connected to the battery terminal apart from the shunt or, apart from the wiring to the monitor, anything to the shunt terminal to which the battery is connected. All charging and loads must be connected to the other terminal of the shunt.

The controller is a PWM type (pulse width modulated) This means that as the battery becomes charged the output from the controller becomes broken into a series of pulses, of decreasing duration (width) as the battery approaches full charge.

I believe, but not certain, this pulsing is fairly slow. Possibly slow enough to see a fluctuating reading on a voltmeter.

My overall feelings are than the solar panel may not be working properly. You do say you get 19.something volts when the small battery is connected but that the battery volts is only 12.5. 12.5 is not going to charge anything. It suggests that the battery is not fully charged and that the solar panel is not charging it either.

But it could be a controller problem.

I would disconnect the controller and wire the solar panel to the battery directly. As the battery charges you should see the volts rise to around 14 or so once it is charged but then continue to rise further. If not suspect the panel. If,however, you do get those sort of readings then suspect the controller.
 
I just added a solar panel and first connected it directly (via the controller) to the house batteries. Batteries were half discharged, went away for two weeks, came back, batteries fully charged. BUT, according to the Mastervolt amp meter, the solar panel was making no difference to the amps being drawn in use.
The reason was that I had connected it to the batteries, not the output side of the shunt. When I changed this, all was working perfectly.
 
VicS has a good point about the pulsing charge. Some voltmeters do not read on a continuous basis but on a sample rate of anything from 3 to 5 times a second, and then average that out to the display unit.

You may be getting uncertifiable readings from the interaction of the charger and the voltmeter.
 
I'd be suprised if the voltmeter and charger managed to stay synchronous for any length of time!
 
Stupid question - but what is the voltage of the domestic batteries at rest - ie disconnect them - leave them stand whilst you have a cuppa and then measure the voltage on them ...

VicS says at 12.5v you're not charging anything - but this isn't strictly true - you could well be charging a duff battery which sits at <11v at rest ...

I had an old car battery I wanted to charge up to test run an Eber - it took ages using a normal mains charger - resting volts was 8! needless to say it didn't hold charge for long and required the charger on there to keep it going whilst I ran the Eber .. next stop was the tip ... BUT ... the point is - whilst it was charging I could measure the volts across it and they were around 11v to start with ...
 
Given that the panel is only 45W (i.e. it can output about 4A at 12V) and the battery capacity is 210Ah, the panel is not going to be able to lift the voltage on the battery much.

The way to see if they are being charged is to stick a current meter in series with them, connect the panel and see if anything up to 4A is flowing into them.

If the baterries are flat, at 4A, it will take 50 hours to charge them. Given that flat is typically around 11.8V and full typically 12.5V, you are not going to see the voltage rise - it's too slow, 0.7/50 is 14mV per hour.
 
I don't think the house batteries are flat, the BEP is giving 12.5 volts, but I do think the solar panel isn't working or isn't connected properly. We have the same solar panel and charge controller. It gives a constant 13.7 - 13.9 volts only the amps change. At mid day with the shadow of the boom across the panel we only see 0.4 amps, however by mid afternoon when the sun has moved round to clear the boom we are back up to 1.9 amps, probably as high as it's going to get given the panel is mounted flat on the deck.

Some work with a portable digital meter should find the problem.

Simon, the later Solar 135TLs could be altered (I think from searching the net) for different battery types but as I don't have a manual for ours or know if its an early type or not I can't change ours. Had a look inside for something resembling "dip switches" but couldn't see any. You may have the later type which can be adjusted.

Pete
 
P7 makes a valid cautionary point. Some solar panels (I stress some) will lose output dramatically if part of the circuitry is obscured by a shadow; others, with cleverer more complex circuits, avoid these losses.
 
Indeed, we are in Portmsouth harbour. When a Port Solent gin palace motors past at 10 knots the wake rocks the boat to such an extent you can see the voltage rise and fall as the angle of the panel to the sun changes :(

Simon, the good news is once sorted it will keep the batteries nicely topped up. Oh one other thing we have noticed, ours is connected to the house side of the BEP VSR, rather than the recommended engine battery side according to the Merlin documentation. The upshot of this is when the panel reaches 13.7 volts each morning at some unearthly hour the VSR kicks in and connects the engine battery to the house batteries so charges that as well. The VSR and its LED does go out eventually but only after dark.

http://www.power-store.com/view-item.asp?itemid=1155&id=199&

Pete
 
I don't think the house batteries are flat, the BEP is giving 12.5 volts
Click to expand...
a fully charged and rested battery should give at least 12.7 volts preferably 12.8.

12.5 volts from a battery which has not been subjected to any load for 12 hours would only correspond to about 70-80% of charged.

A good suggestion to check the current with an ammeter although if it is all correctly wired the battery monitor should indicate that is is charging. It will display the net current in or out of the battery.
 
Many thanks everyone.

I did have the output connected to the shunt, and I did check the open voltage from the panel to make sure it was working.

But the answer is(was) - connect the output of the charge controller to the battery having covered the panel and there being NO output from it. Works fine now :-))

A case of RTFM at least twenty more times. What I said in reply to Sarabande is true, but previous to this in the Solar Panel manual is the clue. My fault entirely as I was referring to the charge controller manual when installing the charge controller, and that procedure doesn't mention covering the panel. Silly me! Just happy I haven't damaged anything.

Thanks again everyone

Simon
 
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