charging lead acid battery

[rcaddict]

just heading out to fly and just realised my 7a 12v lead battery is not charged, dont have time to charge it but was wondering if I connected to cigar lighter socket - would that give a charge ??

[Cuban8]

Whatever you do don't connect a sealed gel 12V battery to anything other than a proper charger specifically designed for those batteries.

[Martin Harris - Moderator]

It will put charge in but will almost certainly damage the battery due to uncontrolled charging at the car's charging voltage - these are designed for charging at 0.7A which is probably regulated by careful control of the charging voltage or current pulsing on your normal charger.

Better to plug your charger in to the accessory socket if you have a 12V one - or use an inverter and mains charger. You won't get much charge in but it may get you flying - top up all the time you aren't flying...or hope one of your club mates can lend you one.

Alternatively, rig up a 3S LiPo to use as a substitute.

Edited By Martin Harris on 26/06/2016 10:18:04

[Shaunie]

Yes it will charge, a bit.

It also depends how flat it is and how long it has been flat for. The longer a lead acid battery has been flat the more stable the lead sulphate on the plates has become. If that battery has been flat for some weeks it could take 48 hours (or more) to charge. Always recharge immediately after use as they detest being left flat.

Shaunie.

[Shaunie]

**LINK**

Batteries vary but this may give you some info. Max charging current is 1.75A in this case. Cyclic charging voltage is given as up to 15V (bit much in my book) most cars typically charge at around 14.5V (unless it has a Calcium battery, in which case it is higher). The problem is controlling the charge current which causes excessive gassing if it is too high.

Shaunie.

[Denis Watkins]

And Old G. you would certainly blow the cigarette socket fuse. The 12v accessory socket is higher rated. As a quick fix, a car battery charger would do the trick, set at auto, or if manual set at 1A. It would invalidate your car guarantees to uprate your cigarette lighter to a 20A fuse in emergency, but best use a mains charger as you suspect.

[Shaunie]

I very much doubt if the charging current would exceed a couple of amps. The voltage drop in the cars wiring will be significant and the cable length from the socket to the battery will add additional resistance.

The problem is that there are so many unknowns without a meter in series you will have no idea what the current will be.

What car is it btw?

Shaunie.

[rcaddict]

thanks guys - I have put that idea to bed now !!!

[fly boy3]

Slightly off topic but close. My next door neighbor has sold his motorbike and and offered me his 12v trickle charger. This he says can be left on when battery not in use. Its called an Optimate desulphater. Would this be ok to use. Cheers

[onetenor]

What do use the battery for and why Lead / acjd please ? and yes that trickle charger would be ideal Snatch his arm off

[Cuban8]

Just to reiterate. The small (i.e. 12V 7Ahr) sealed lead acid gel batteries that we often use in our flight boxes for starting/pumps/glowdrivers etc require a totally different charging regime to large sealed automotive or leisure lead acid batteries with liquid electrolytes.

Sealed gel batteries require both very careful current limiting and voltage limiting during a charge and a standard auto battery charger/trickle charger (or charging via a car's alternator) will almost certainly cause an excess of both, leading to over heating, pressure build up - and if you're really unlucky, failure of the battery case. Only use a dedicated gel battery charger or a programme suitable for these batteries that can usually be found in many Lipo field chargers.

I've seen the result of a club mates attempt to charge a gel battery from a normal car battery charger and it really wasn't pretty.

 

 

 

Edited By Cuban8 on 26/06/2016 13:07:41

[Peter Beeney]

This 12 volt battery issue has cropped up before, indeed on more than one occasion as I remember, so I really couldn’t resist repeating what I said back then. A long time ago, back when I was still working, I owned a Peugeot 205 van with a 1.9 naturally aspirated diesel lump. At one time I happened to come by a Gates 12 volt SLA battery which was a time expired replacement. By coincidence a mate wanted a battery so I gave him the one from the van and used the Gates myself. Size wise it was bigger than our flight box version, but only about half as big as a standard car battery; so I had to pack out the bottom and sides of the battery box with styrofoam to get it to fit. Mods to the holding down strap, too. Connections by threaded stud so I had to cobble up a couple of straps there as well. Officially rated at 100Ah capacity, but I’m sure it was much better than that. This battery was on my van for 7 years and 200k miles and was still on it when I sold it. To the mechanic that serviced it, actually; and as also as I said before, frequently used to jump start some of the reluctant works vehicles in the depths of winter. It never once let me down…

For work purposes I needed a steady portable and dependable DC voltage supply, so I acquired 4 DryFit SLA 7Ah 12 volt batteries from RS. They were a brand new idea at that time, and quite expensive; exactly the same size as the 7Ah Yuasa model box jobbies; I made the necessary leads to connect them together in series or parallel as required. Generally little current was needed but often over a lengthy time period. I kept them charged with my portable variable voltage supply, but in an infrequent emergency they were parallel together and hooked up to the trusty van. Good one, that van, on a couple of occasions I did some night time emergency equipment tinkering using the headlights… inside a building, as it happens, so I was very loath to run the engine.

I often used them for modelling, too, so they came with me when I retired. Cases cracked and the sides collapsing inwards, but they still just kept right on delivering… I’m pretty sure the Gates is of American origin, at least, and the DryFit was from Germany, I believe. In my opinion these surely were the king of kings amongst batteries, of all different shapes, sizes and manufacturers.

As usual, this is not a form of instruction or recommendation, just a chronicle of what it’s possible to do and get away with it…

PB

Edited By Peter Beeney on 26/06/2016 16:14:48

Edited By Peter Beeney on 26/06/2016 16:16:37

[Bob Cotsford]

Posted by fly boy3 on 26/06/2016 12:14:07:

Slightly off topic but close. My next door neighbor has sold his motorbike and and offered me his 12v trickle charger. This he says can be left on when battery not in use. Its called an Optimate desulphater. Would this be ok to use. Cheers

The Optimate 4 instructions include gel batteries so it should be fine

[Martin Harris - Moderator]

Posted by Shaunie on 26/06/2016 10:35:38:

**LINK**

Batteries vary but this may give you some info. Max charging current is 1.75A in this case. Cyclic charging voltage is given as up to 15V (bit much in my book) most cars typically charge at around 14.5V (unless it has a Calcium battery, in which case it is higher). The problem is controlling the charge current which causes excessive gassing if it is too high.

Shaunie.

Interesting - I was sure that my Yuasa batteries stated the maximum charge rate was C/10 but having checked both my present one which doesn't show any info and the relevant data sheet, sure enough, a maximum rate of 1.75A is quoted. How much charging time have I wasted over the years?!

[Philflyer]

If you are buying a charger for sealed lead acid batteries don't trust your average fleabay seller. I bought one at the beginning of the year. Advertised as "1/2 Amp trickle charger for sealed lead acid batteries". A bargain at just over £7 (incl. postage). It arrived quickly and looked like your standard wall wart charger, so I connected it to my 7Ah SLA battery in my flight box. An hour later I checked it. The charger was so hot it was uncomfortable to touch and it was happily charging at 1/2 A at 18 volts! Fortunately my battery had not exploded. I complained to the seller in detail and sent him an extract from the tech notes I use to teach my students about (full size) aircraft battery charging and the dangers with SEALED batteries.. Needless to say he was not in the least concerned other than to say if I returned it he would refund the purchase price, minus the postage.