Small solar panel query (1 Viewer)

[pappajohn]

I just can't get my head round it.

Possibly a 50watt panel, I assume 50watt as I haven't seen it.

Multi meter onto Pos and Neg wires and reading 21volts

Its been wired direct to battery with no regulator.
Due to it being such a small panel Will the battery self regulate the voltage down to a more useful voltage or is it just banging in 21volts?
The battery is totally knackered....
After a 24hr charge it shows 13.7v
Only 1 strip light running the voltage drops to less than 5 volts in around 5 minutes.

 

[fat haggis]

It will kill your battery or even a new one get at least a cheap solar regulator on it
It’s not the volts it’s the amps that are important

 

[pappajohn]

It will kill your battery get at least a cheap solar regulator on it
It’s not the volts it’s the amps that are important

My thoughts too but many of these small panels are chucked on the dash and clipped to the battery not needing a regulator.... But the question is do they still bang out 21volts or are they self regulating in some way.
It wouldnt surprise me if it isn't a larger panel anyway.

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[fat haggis]

50w is not that small really or wasn’t a short time ago

 

[Tombola]

too many volts but only 4 or 5 amps. the panel will just keep climbing the volts and boil it.
you do need a regulator Im afraid

 

[pappajohn]

too many volts but only 4 or 5 amps. the panel will just keep climbing the volts and boil it.
you do need a regulator Im afraid

No amps at all today, very overcast so maybe a few Milliamps.
I disconnected the panel anyway.

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[cmcardle75]

My thoughts too but many of these small panels are chucked on the dash and clipped to the battery not needing a regulator.... But the question is do they still bang out 21volts or are they self regulating in some way.
It wouldnt surprise me if it isn't a larger panel anyway.

No. They couldn't bung out 21V whilst connected directly to a lead acid battery. If they did, they'd be pumping 100s of amps into the battery and they simply don't have the power to do so.

However, what will happen is that they will do a reasonable attempt at bulk charging at maximum rate (but somewhat inefficiently due to lack of MPPT). This means the voltage will slowly rise up to 14.4V, just like with a smart charger.

However, once bulk finishes, it will fail to move to absorbtion phase, let alone float. The voltage will go way above 14.4V and result in excessive gassing, eventually destroying the battery.

You may get away with it with a very low charge rating, (ie. 0.05C), as the overcharge will be slight. With a 50W panel, not a chance.

 

[pappajohn]

Just realised where the flaw in my thinking is...... I'm thinking those 5watt panels supposedly to trickle charge a battery.....not a 50watt.
The previous owner of this shed knew nothing about it but had a tinker anyway.
Fridge didn't work.... Yes it does.
Didn't know how to light the gas fire... Gas valve turned off on manifold.
Just the little things like that.

 

[DBK]

To answer your original question the 21 volts you measured would be the open circuit voltage of the panel without load. When attached to a battery the voltage will fall to something around 13 or 14, the exact amount will depend on the state of charge and the amount of sun. It will certainly charge the battery like this and some cheap controllers do exactly this - connect the battery directly to the charger. But these controllers sense the voltage and disconnect the battery when the voltage reaches a higher limit. With use the battery voltage will reduce and at a set lower limit the charger will reconnect the battery. This isn't a very efficient way of doing it but the system works. These are called shunt chargers.

Just seen your edit, if it is a 5W panel it won't do any harm connected directly - or much good but probably better than nothing.

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[andy63]

It will certainly charge the battery like this and some cheap controllers do exactly this - connect the battery directly to the charger.

Thats basically what any true pwm controller does.. or at least that was my understanding...it connects the panel directly to the battery and acts as a switch to control the charge ..
Andy

 

[pappajohn]

Just seen your edit, if it is a 5W panel it won't do any harm connected directly - or much good but probably better than nothing.

Certainly not a 5watt jobby.
My mate had a look on the roof and said it was around 18" Square so I assumed it to be around 50watts.
But he has a strange perception of distance and weight... It could be 3ft by 2ft for all I know
It will remain disconnected until I get my spare reg on it to test.

 

[Lenny HB]

Max recommended without a regulator is 20 watt.

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[Revolvor]

Amazon product ASIN B071ZZ2S84
I've got two of these - one on my shed, and one on my boat. Cheap, but they seem to do a good job. The boat batteries (40 watt panel) were sat at 13.5v after last year's lockdown, and engine started instantly.

 

[cmcardle75]

Thats basically what any true pwm controller does.. or at least that was my understanding...it connects the panel directly to the battery and acts as a switch to control the charge ..
Andy

The difference between a PWM and a "shunt" style is that the PWM will rapidly connect and disconnect the panel to give somewhere between full and no charge, so can do effective voltage regulation. Basically, the "shunt" style has to switch off and can't perform absorbtion phase, whilst PWM can.

MPPT is more clever in that it can have different voltages across the battery and the panel, so can optimise the panel voltage for its maximum power output during the bulk phase, which might not match what voltage the battery is producing. PWM has no choice but to run the panel at battery voltage, which may reduce power output by up to 30% depending on how mismatched they are.

 

[andy63]

MPPT is more clever in that it can have different voltages across the battery and the panel,

That would be my understanding..the fundamental difference between pwm and mppt is that there is no direct connection between panel and battery with a true mppt controller.. whereas there is with a traditional pwm..
Andy.

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[Raul]

The difference between a PWM and a "shunt" style is that the PWM will rapidly connect and disconnect the panel to give somewhere between full and no charge, so can do effective voltage regulation. Basically, the "shunt" style has to switch off and can't perform absorbtion phase, whilst PWM can.

MPPT is more clever in that it can have different voltages across the battery and the panel, so can optimise the panel voltage for its maximum power output during the bulk phase, which might not match what voltage the battery is producing. PWM has no choice but to run the panel at battery voltage, which may reduce power output by up to 30% depending on how mismatched they are.

A PWM pulse with modulator will only modulate when charging reaches constant voltage ( absorb). Until then the panel is directly connected to the battery, and the battery voltage and resistance is doing the pulling down of the panel voltage. Once the CV is active, the PWM it switches at very high frequency on and of to maintain the voltage set. So until CV mode the PWM does nada. The battery pulls the panel down.
You will end up with amps in -amps out, as long as the panel voltage can stay above battery voltage.

The mppt is a dc buck converter, you still need higher panel voltage to charge a lower battery voltage, with added dc conversion, that results in power in- power out. No extra voltage is lost. The added bonus is, it tracks the maximum power point of that time. The more samples it takes the more modulation will do. There is even a therm for fast and lazy tracking.
Even more clever mppt chargers used on wind turbines that have buck AND boost converter, you can have a lower OR higher input than the battery.

 

[pappajohn]

He has a new 110ah battery coming tomorrow and the panel WON'T be getting connected until everything else is checked and sorted.
Think I've located the split charge and fridge relays so that's the next thing.
Water pump was running very slowly and needed a tap with a spanner to get going.... Tried it with the valve block off, no better so took it off to have a look.
Took the armature out and the fixed magnets were stuck to it. They had debonded from the motor case. I'm surprised it ran at all.

 

[Phill D]

I detect your enjoying this pappajohn

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[pappajohn]

I detect your enjoying this pappajohn

Nice to get me hands dirty again.
Very dirty soon, he wants the cambelt changing.

 

[Phill D]

Nice to get me hands dirty again.
Very dirty soon, he wants the cambelt changing.

does it have one,

 

[pappajohn]

does it have one,

You have me thinking now. I only mentioned today it looked like a pushrod engine.
There is a plastic belt cover but it may only be the injector pump belt.
Everything else is by visible aux belt.

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[Phill D]

You have me thinking now. I only mentioned today it looked like a pushrod engine.
There is a plastic belt cover but it may only be the injector pump belt.
Everything else is by visible aux belt.

i am really not sure !!!! when ford introduce belts and on what engine.. i guess its not difficult to find out with that cover off.

 

[cmcardle75]

i am really not sure !!!! when ford introduce belts and on what engine.. i guess its not difficult to find out with that cover off.

I remember changing the cambelt on a 1983 Ford 1300 CVH when I was at university. Although hopefully, this doesn't have that particular engine!