Lead acid battery charging

I have a remote garage (No mains electricity) which has a 12 volt DC supply from a battery / solar panel charger. I use the 12v for lighting (12v LED GU10 bulbs), also for an alarm system using a mobile and SMS messaging.

It would be great if I could trickle charge the 6volt battery of the Austin 7. I have surplus 12volt DC energy. Has anyone seen a 12volt to 6volt charger?

I suppose I could convert 12v DC via an inverter to 240v AC and then run a 6volt DC charger, but that seems a long way around.

Any ideas out there?
BobH

Edited By Speedy Builder5 on 10/08/2018 17:02:50

I used to charge my 6 volt Honda moped battery from my 12 volt battery charger by connecting a side light bulb in series with the battery. Different wattage bulbs give different charging current. I'm sure there is a more modern sophisticated approach costing an arm and a leg, simple but it worked and never ruined the battery either . John

Plenty of ways to do it. I would use a 2N3055 power transistor with a potential divider across its base ( but with a few more components). Likely only applicable to floating an already charged battery, mind. There are voltage regulator chips out there these days.

Digital pulse width modulated regulator is easily built using discrete components or with a suitable IC e.g. LM2575 if 1 amp is enough. Basically charges capacitor to preset voltage which feeds the load via a diode. Scads of circuits around.

Built one maybe 40 years back which worked well.

Clive.

Rather than a 2N3055 I'd go for a buck converter because they're so cheap these days.

As John suggests a 6v side light bulb (15W) in series will also do the trick. Keep an eye on it though, as the battery charges, the bulb will dim. Once that happens disconnect. If you don't the voltage on the battery will rise to 12V and do the plates no good if left for too long.

Dave

I use a DC adjustable step down power supply module off Exxx to reduce 5 vdc to 1,5vdc, seems to work OK. Saves a lot of batteries!

.

Would that be Esso

..or buy a second 6v battery and put them in series? They don't look too expensive. I suppose the worry is that the cells wouldn't all be quite the same capacity.

pgk

Any use? :- **LINK**

I still have a few BC107/8/9 and 2N3055 transistors knocking around. A zener diode across the battery would avoid too much gassing (which would be enemy number 1), should the battery voltage rise too far?

Trying to "trickle charge" a PbA battery via a bulb will simply overcharge it and then proceed to convert the water to gas. Probably about the worst thing you could do. Apart from drying out the battery, it will generate a fine explosive gas mixture.

Why not just buy a proper 6V / 12V battery charger? It will cost you less than the replacement battery you will otherwise need to buy.

If you insist on trying to charge it with a DIY circuit, use a regulated constant voltage source of 7V (14V for a 12V battery). It's no great coincidence that this is the voltage generated by the alternator regulator and corresponds to the float voltage of a fully charged battery.

Murray

The LiPo charger I use for charging my kids (ok, mine and my kids) radio controlled car batteries is completely programmable to charge any kind of battery and runs from a 12v supply (in my case my shed lighting is the same setup as you, LEDs and Solar). You can choose to charge a Pb battery of any set voltage (up to a point!) at any charge rate you wish, or automatically changing it to suit demand.

It's a Turnigy Accucel 6 if that helps. Charging the RC cars from a car battery and solar panel does make it completely "Green" as well!

Edited By Jon Lawes on 10/08/2018 21:46:42

.

Your other advice is very wise, but [with respect], may I suggest that you re-read the opening post.

MichaelG.

Jon beat me to it -

RC chargers that work from 12v are in abundance - the link is one I have for small batteries - can give up to 5 amps and is fully automatic - press a button to start the charge and it shuts off when done.

Only problem ( if it is a problem) is that these type of chargers will not function as an always-on trickle charger - they all shut off when the battery is 'full' and you have to manually re-start the charge.

Joe

**LINK**

Those lipo balance chargers are brilliant &when i gave my rc stuff to my nephew the only thing i kept was the charger! Why don't you just use a small solar panel to trickle charge your 6 volt battery ? You don't need or want a lot of current to do this so a solar panel that outputs 12volts and a simple regulator consisting of a 6.8 or 7.5 zener diode across the battery terminats ( may need a few in parralell to handle the current ) to regulate the voltage to around 7 volts .

The problem with using a device running off your solar charged 12 v system is it will need to be ultra efficient otherwise it could drain that system to death !

Lots of advice - Thanks, but not there yet as the system needs to both charge and trickle charge. BUCK convertor wouldn't do that also o/p is 6v and not 6.8 for charging. I didn't want two solar panel chargers, one for 12v and one for 6v, so that idea is rejected. I did find a unit, but a bit pricey **LINK**
and then a cheaper system **LINK**

but getting them in from the USA may prove a bit costly. The search continues.
BobH

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BobH

It's true that the specific BUCK converter that S.O.D. linked is fixed voltage, but there are many adjustable ones available. Search for LM2596 on ebay, and look at the modules with a voltage display ... I use these very successfully with LEDs so I can't really see why they shouldn't do service as a trickle charger.

MichaelG.

Your OP states clearly that you only want to trickle charge your 6volt battery , please make up your mind and tell us what you really want !

If you just want to keep the already charged battery in good condition you need to float charge it. For a nominal 6V battery you need a constant 6.8V that will provide whatever current is needed to compensate for the self discharge. 6V is not enough and will keep the battery in a partially charged state.

Just buy a buck converter and set it's open circuit output to 6.8V.

For more information see for example this site.

https://batteryuniversity.com/index.php/learn/article/charging_the_lead_acid_battery

Russell

Why not use a solar panel ? I bought them to charge the 6v battery on outside security lights. You can get them complete with electronic gubbins to limit the charge, very cheap. I've had one for about 4 years now with no problems. PS I know you said you didn't want to use another panel.