Three cheers for Solar Charging!

[MikeHA4]

Clearly my Peugeot's 6 yo 60Ah battery isn't quite so good. Over three days on charge and not got beyond 12.6v steady when evening comes. The 110Ah camper battery, being new and on the west-facing 12W panel, yes, twelve it says on the box, has in three days from a bit over 90% charge got to 12.77V. I think Mr. Ecosse's TR7 must have a very good battery condition.

[MikeHA4]

Its some days now that the Pug car has been either in use or on the small panel charger. It doesn't want to go over 12.6V settled. It is well over 13V immediately after stopping the engine of course. The flashing indicator on the panel I don't think is very helpful. It shows the panel to be generating, nothing more. Even if that is only 4V in low light, which is effectively 'off' as far as putting anything through a 12V battery is concerned.

The VW T4 camper is doing well on the big panel - 12W max output and no flashing gizmos. In the sunshine today, it achieved a 'system voltage' of 14.76v and the battery at 13.50V. It has settled this evening at 12.89V. It has been brought up from 12.58V over about a week, in a 110AH battery.

[MikeHA4]

This morning, Easter Monday Bank Holiday, T4 is static overnight at 12.8V. Great. Pug is static at 12.56V, not used yesterday. Oh, it'll still work the heaters and starter but as it cost £30 six years ago, I'm thinking its soon for Battery Heaven... Or shall I bung it on the automatic charger for a day?! Of course, everytime I unlocks the door, the modern gizmos clunk and click using electricity!

[ptitterington]

I have one but not convinced it works. I dont have a volt meter but if I touch the ends on my tongue I feel electricity.
I used it to keep an old dumper charged but maybe that was asking too much of it.

[MikeHA4]

What condition was the dumper battery? Also, was the panel outdoors? It would need to be the weatherproof type for that or encapsulate it in some way! The 1.5W which is on the car dash certainly is putting out current. The 12W, hanging in the Garage Window is doing extremely well into a few months' old 5 yr warranty Elecsol 110Ah... Actually, I had two exactly the same 60Ah's new at the same time. One has already been scrapped (was in the camper) so I'm not surprised the one in the car isn't likely to be at its best!

I have checked the off-load voltage of these panels. Even in cloud conditions, they are at 18V or so. Around 22V in sunlight, so they ought to deliver a charge..

Smaller output altogether, is a plug-in charger of 350mW for long-term trickle charge maintenance. Even that got a system voltage up to nearly 15V over a winter period. So low power is almost fine..

[kittyfell]

To get the best from a solar charger it should really face due South, not West. They definitely work!

[MikeHA4]

Agree, Kittyfell, I'm quite pleased. I have only a window to the west but its working fine. It was the first part of this topic encouraged me to go out and by one, followed by the next! I don't want the 110Ah suffering, I want nigh on ten years out of that! Unless it got sold with the camper, say.

[brian]

Hi got mone from maplins over a year ago as the battery on my 1990 bmw 3 series kept going flat as I do not use it a lot,since having the solar panel (9.99 from maplins) I have had no problems,cheers,Brian[frame][/frame]

[MikeHA4]

Thanks for that, Brian - I was put onto them by the Originator of this thread. You can read and see my reports of progress. So far, so good! The big panel isn't so cheap though, £50 but it was still reduced in a sale. I've seen that it charges rather than simply maintains so thats good for the big battery. It can be made part of a bank of panels if wanted, too.

[xpress]

i wonder how the 50 quid solar would fare on a camper ..

[MikeHA4]

Its going jolly well, Mr Xpress! Battery is now up to 12.83V static (before the light levels rise in the morning) from a 12.58V start a couple of weeks ago. 'Tis a big capacity battery and vehicle has modern-day electronics drawing from it all the time. Other thing was, in the winter it will get less daylight and the garage window only faces slightly south of west. I don't want to put it outside, though it is weatherproof. I wanted to try the big panel as a charger rather than just a maintainer. Value was £70 but got it for £50. It is proving an interesting gamble. It has a 5 year guarantee so, the equivalent of three pints of beer a year for five years..

[MikeHA4]

Bingo! or is it 'Snap'? The big battery has hit a static voltage of 12.85 so I've caught up with Mr. B. M. C. Ecosse's TR7. The Peugeot battery isn't doing so well, it is back at 12.58 again this morning. Still works though but I'll need to watch it...

[xpress]

hi there guys, i was wondering if you could put me in the right direction for testing batteries and assessing condition.

what sort of current should i be getting in volts on the multimeter for a healthy battery that's just been charged on the car battery charger and left to stand for a day? any tips for testing and assessing? any other tests i can do, say testing amps? also if they're maintenance free they can't be helped but is there anything you can do to ones that can be maintained, how does adding to the electrolyte level boost the volts and by how much? as you can see i just need a few pointers. so 12.8ish is good and 12.5 not so good?

i have a couple/few batteries to test and maybe throw out if they're not working.

[xpress]

also with a 50 pound panel from maplins, i guess you could charge portable things and run a tv set with not much trouble and still charge/maintain a leisure battery in a camper right? i guess you could use pretty much anything but hair straighteners and vaccuum cleaners on the battery and it would stay charged and maintained with a big solar? what things could yo use and what things could you not use?

[MikeHA4]

Hello, M. Xpress! Well, reading your post, I think first to recap that Volts are a measure of electrical 'pressure'. This exists in the supply, even whether something is switched on or not. Amperes are a measure of electrical 'flow' and indicate how much (volume, if you like) is passing along the wires when an appliance is switched on. The actual amount of energy used is measured in Watts, a multiplication of the Volts x Amps.

When '12V' batteries are 100%, fully charged up electrically, they have a voltage reading of around 12.7 v to 12.9 v. When they are discharged to say 40% capacity, the voltage will be lower, at around 11.9 v. Test this with a multi-meter set to the correct range. Any voltage below say 11.5v. is very seriously discharged. 10.5 v. indicates a completely flat battery with no reserve of energy. Left in this state, batteries will physically deteriorate such that it is generally difficult to re-instate them.

Car 'Starter/Lighting/Ignition' batteries are physically constructed specially to do this job.

The electrolyte, which is the liquid is a dilution of sulphuric acid and distilled /de-ionised (pure) water. When the battery is fully charged, the Specific Gravity will be around 1.25 compared to water, which is 1. This is the time when the acid content is strongest. At any time, the electrolyte is a dangerous material.

When a battery is seriously discharged, less of the acid will be in the electrolyte so the S.G. will be lower, closer to 1, maybe 1.15 or so. The level of liquid can also be lower. It is still a dangerous material.

The acid doesn't wear out. Loss of liquid (without leaks) is due to overcharging and evaporation of the water content. It is this we replenish with battery top-up for those where the cells are accessible. They should be refilled when charged up, to a level of 1/4" over the plates seen inside.

From this, you can see the easy tests are on voltage. Don't add any electrolyte (acid and water) to any battery unless you know it has been knocked over and the original lost. Adding water to battery cells will weaken the strength and is only done to cover the plates as above. No adjustment to acid should be made in attempts to change battery voltage.

Sealed batteries operate at a slightly weaker mix, are vented discretely and provided are charged properly at the correct rate of charge, won't lose liquid over their life.

Yes, 12.8 v showing after being on a car battery charger and then left to stand for a few hours is good. Or, on the car of course. 12.5 v is OK but if the battery doesn't come up above that, it isn't getting or keeping a full charge so needs thinking about.

News on mine, is that it is back at 12.75 now so I'm not worrying, just remembering it is 6 years old. It was a £30 cheapie with a 12 month warranty only!

To test a battery in a discharge mode, requires 'special' equipment and doesn't do the battery much good either. Best thing I can suggest is a normal situation equivalent: whilst reading the battery voltage, make sure the engine won't start (take off HT lead or something or rotor arm) and then operate the starter. Watch the voltage whilst the starter is working. It will drop probably to 11 plus volts. When the starter motor is stopped after a few seconds, see how the battery voltage recovers. If the voltage stays low, the starter runs 'slowly' etc, indicates a tired battery. My example was a drop to 9.5v when the starter was operated (diesel engine, heavy to turn) which the AA man confirmed meant 'You need a new battery'!


Your question about an 11Watt panel. this is about 1amp output during maximum daylight conditions. This certainly recharges the battery and might well allow operation of a 12V TV set over a week with no other source of charging. Some battery reserve will be drawn over that time and the charging panel will put something back. Anything using more than five or six amps (60W) for a few seconds, which means water pumps OK really but not much else. No mains inverters connected to hair dryers for instance!

Theres more to this to refine the position; for instance it is useful to know that as a battery recharges, the charge rate reduces for technical reasons. It probably takes longer to put back the last 10% than it does the first 40% for a half-discharged battery, roughly, anyway! Also, about 10% more charge has to be put in than the battery capacity, to fully recharge it. Inefficiencies creep in.

Hope this helps your understanding.
Mike

[MarkyB]

Thank Mike, very informative write up.
Am I right in thinking the resistance goes up the more the battery is charged?

[MikeHA4]

In the sense that the charge rate reduces? I believe it is the internal resistance plus the effective resistance of the rising battery voltage at the terminals. This opposes more and more strongly, the charging voltage and current externally applied. It is known as 'Back - EMF' where 'back' I hope is self explanatory and EMF means Electro-Motive-Force. Electrical energy, in other words. It behaves as an increasing resistance.

Goodness, I do hope I'm right about all this! I know its not too far wrong, anyway, for most users of battery systems to appreciate the complications!

Mike

[kittyfell]

Good explanations! The internal resistance of the battery remains effectively constant, the charge rate will drop off if the charging source is at a fixed lowish voltage, the charging rate being driven as explained by the difference between the charging source voltage and the battery voltage. To get 'constant current' charging a high source voltage is used with an inline resistor to limit the current flow, and so the rate remains effectively constant even though the battery voltage rises as the charge in it increases.

[MikeHA4]

Thank you, Mr Kittyfell if I may! I rather surprised myself actually, when I rattled that lot off the other evening and read it through before posting. I recognise what you say too and Markyb seems to appreciate the long spiel bit. The danger I thought was, of getting in 'too deep' but clearly questions are raised, like Xpress's, and I often think some of the technicals will help remove the mystique for people. It has to be fairly clearly explained though to better the situation rather than make it worse!

[xpress]

i just checked in on this post today, thanks mike and all for explaining so thoroughly! it definitely helps know this to maintain the most from our batteries.

thanks again.