At the weekend, I moved my car on the drive and noticed my reversing camera had stopped working with the error "Park assist not available". I used OBDeleven and scanned the car and had 27 faults related to electrics: implausible signals, lights not working, trailer errors, all sorts. Despite turning the car off and on a few times, the errors didn't go away. Noticing they were all electrical, I stuck the car on a battery charger as it had been sat for a couple of weeks and later the same day, tried it again and all was fine, including the reversing camera.

 

So I dug out my solar charger and I have now left that connected. It's an 8w one so quite small, but unregulated. It gives a no load voltage of 22v but when connected to the car, it gives 12.8. Is there any harm in leaving this connected long term do you think? I'd rather leave a proper battery conditioner connected, but needs must. What do you think?

 

Thanks!

 

Nick

By asking the question, you have your doubts already!

 

Really it should be regulated to 14.8v to stop overcharging especially for AGM spec batteries. If you are lucky enough for it to be that sunny you get peak charge out of the solar panel for a while, its possible to boil the battery. With a potential difference up to 22v vs 12v of the battery, there is the opportunity for a higher than necessary current to flow though it.

 

Overcharging long enough causes the battery to 'boil' as it splits water content into Hydrogen and Oxygen gas. If there is enough gas pressure inside, this gets vented so you lose a very small quantity of water from the battery each time it does this. EFB's have way more electrolyte than AGM's but the long term risk is that the stronger the electrolyte becomes as the water level drops, the quicker the decay of the plates happens shortening battery life. Also the battery can warm up which also is detrimental to the life of the battery by accelerating plate decay.

 

Best get a charge controller or just charge the battery with a decent plug in charger once every couple of weeks.

 

Otherwise, if you have stop start, let it idle until first idle stop cuts in.

Edited 31 March, 20206 yr by BigEjit

An 8W rated solar charger will probably manage 0.8W in reality if you're lucky. Measure the current it's putting into the battery by putting a meter (on a mA dc range) in series with one of the connections . I bet you only see a very small number of milliamps.

 

I would say the chances of the voltage exceeding 14V when connected to the battery are zero.

 

See my post below dated 15th April. The struckthrough info above isn't correct. FAO @NikTheGeek and others reading

 

Edited 15 April, 20206 yr by Wino

Hi,

 

if you are any good with electronics you can make a constant voltage charge controller with a LM7805 chip, or look on Amazon as I am sure they will have one

 

John

Just measure the voltage across the battery terminals when you think it ought to be doing its peak output, I think you'll find that very reassuring, and it will rapidly make you realise there is no need for any sort of regulation on such a small panel.

2 hours ago, Wino said:

Just measure the voltage across the battery terminals when you think it ought to be doing its peak output, I think you'll find that very reassuring, and it will rapidly make you realise there is no need for any sort of regulation on such a small panel.

I did. 12.7v without the panel connected. 12.8v with it connected.

  No cause for concern then.  

On ‎31‎/‎03‎/‎2020 at 14:21, Wino said:

An 8W rated solar charger will probably manage 0.8W in reality if you're lucky. Measure the current it's putting into the battery by putting a meter (on a mA dc range) in series with one of the connections . I bet you only see a very small number of milliamps.

 

I would say the chances of the voltage exceeding 14V when connected to the battery are zero.

 

 

I have to retract this post (will strikethrough in a minute) as I have just taken two photos that prove it to be duff information (based on measurements of a rather smaller panel years ago that was very disappointing).  I have a 7.5W rated panel now that I've had sitting on the car roof facing directly at the sun, at a favourable inclination.  Battery was reading 12.4-ish before connecting, this is after half an hour:

 

 

 

With current meter inline it was reading around 0.5A, which at that voltage suggests the 7.5W spec is being achieved.  Wouldn't want to charge at that voltage for long so turned it away from the sun a bit which dropped it straight down to lower output, obviously.

Won't do as much behind a windscreen; it was managing only 300mA the other day in one of the other cars in similar sun, inside the windscreen, which didn't result in a between-battery-posts charging voltage of any more than about 13V.

 

So some form of regulation might be a good idea after all. Will see what I can come up with as a cheap and cheerful bolt-on. High power zener diode might do it.

Something like this in parallel with the output cables ought to do it I think, with cathode to positive ought to work I think, I'll try it.

https://uk.rs-online.com/web/p/zener-diodes/7743293/

 

 

 

3 hours ago, Wino said:

 

I have to retract this post (will strikethrough in a minute) as I have just taken two photos that prove it to be duff information (based on measurements of a rather smaller panel years ago that was very disappointing).  I have a 7.5W rated panel now that I've had sitting on the car roof facing directly at the sun, at a favourable inclination.  Battery was reading 12.4-ish before connecting, this is after half an hour:

 

 

 

With current meter inline it was reading around 0.5A, which at that voltage suggests the 7.5W spec is being achieved.  Wouldn't want to charge at that voltage for long so turned it away from the sun a bit which dropped it straight down to lower output, obviously.

Won't do as much behind a windscreen; it was managing only 300mA the other day in one of the other cars in similar sun, inside the windscreen, which didn't result in a between-battery-posts charging voltage of any more than about 13V.

 

So some form of regulation might be a good idea after all. Will see what I can come up with as a cheap and cheerful bolt-on. High power zener diode might do it.

Something like this in parallel with the output cables ought to do it I think, with cathode to positive ought to work I think, I'll try it.

https://uk.rs-online.com/web/p/zener-diodes/7743293/

 

 

 

 

I shall go an double check my battery voltage right now and report back!

 

...

 

...

 

Looks fine. 12.47v in full sun on the dash inside the car. Maybe it would generate more if it was outside on the roof, but its not.

 

I originally got it to charge the battery on my jetski which gets rarely used, but the battery is tiny in that thing so I never used it. I've finally found a use for it now! BTW, that looks identical to the panel I have, even down to the folding leg. Mine is waterproof (aparently). Anyway, it looks ok to me...

Edited 15 April, 20206 yr by NikTheGeek

Good news, but please keep an eye on it voltage-wise, and I'll feed back soonish about implementing a cheap and cheerful regulation, to be on the safe side.

 

18 hours ago, Wino said:

Good news, but please keep an eye on it voltage-wise, and I'll feed back soonish about implementing a cheap and cheerful regulation, to be on the safe side.

 

Don't know if it make a difference, car circuit-wise, but the charger is plugged in by the cig lighter inside the car, not connected directly to the battery...

As long as the ciggy lighter socket stays live 24/7 it should be OK, there'll be tiny losses through a couple of fuses on the way back to the battery, but insignificant.

My car wouldn't start the other day due to a flat battery with standing round, took the battery off and charged it in the house, then invested £25 in solar charger from Halfords, seems to be working perfectly so far. 👍

I've been using this 15W solar panel from Amazon Saronic 15W 12V during lockdown when I noticed that the battery voltage was down to 11.7V. Since using it it's keeping the battery voltage (at the 12V socket in the centre console) around 12.6V.

This little gadget is useful for monitoring voltages and currents etc too.

 

You stick it inline with your solar charger to see what is going in.