lead acid battery charging, will this work

Members of out ME club seem to think that batteries charge themselves if they just take off the flat one and put it in the shed. We've actually bought a clever charger but very few will take responsibility to take them home (no mains power at track).

Most cars have a power outlet in the boot nowadays. If I make up a plug and 2 croc clips can we use this to charge batteries, perhaps with a low resistance in series to limit initial charging current (brake light bulb?). Not sure what happens when you try to start the car, does it try to draw off the little battery as well?

Are you thinking of charging from the car battery or running the engine of the car to charge the battery(s). When I towed caravans you could buy a splitter which would block the second battery charge until the cars battery was fully charged, I would also fit an ignition controlled relay in the circuit to stop the car battery being drained when the ignition is off, you may have to look at what the fuse rating is for your accessory socket as the wiring may not be man enough to charge a battery.

Martin P

Am I to understand that it is your intension to charge the club battery from your car whilst the car is stationary, with the engine switched off. I think you may soon have two partially flat batteries. Modern car batteries are not designed to discharge slowly, they give a lot of energy to the starter motor for a short time, then the alternator takes over. I think your club battery will be a leisure type which gives a smallish amount of energy for a long time, almost the opposite to the car battery. If you want to charge the club battery from your car whilst on the move with the engine running, then you will need a split charge relay as used to be fitted to motor homes. No doubt motor home have an intelligent type charging system now days, with flashing LEDs, many surface mounted chips and plenty to go wrong. Having looked under the bonnet of a few modern car I couldn't even guess which wires are which, so many wires and nothing identified. Also, I do know some cars need to their ECU reprogrammed if a tow bar is fitted, as they are using more current than expected, so be cautious. John

Canal boats have long been using small wind turbines to charge batteries. Any options there?

Solar panels are fairly cheap these days. A reasonably sized one on the shed roof, possibly with a charge regulator, would recharge through the working week, ready for the week-end.

The three (rather basic) motor homes I've had have used nothing more sophisticated than a relay that switches the leisure battery into parallel with the starting battery when the alternator is generating. The use of relatively narrow gauge wire seems to be used to prevent problems!

YMMV...

Neil

I would make up a roster so every member has a go at charging the batteries !

The charging controller from a dual battery system used on a 4wd sense the alternator output and main battery voltage so it will only charge the auxiliary battery when the engine is running and the main battery is fully charged ( alternatirs never fully charge a battery as thier output is typically 13.7v not the 14.4 v needed to fully charge a lead acid battery .)

The controller will also limit the current in two ways :

It ramps the current up slowly as deep cycle batteries don't like a lot of current to start with and they limit the total current as the construction of a deep cycle battery is not designed to deliver or recieve a large current like a starter battery can .

Please also be aware that when charging a lead acid battery it will give off hydrogen gas so if it is locked in a boot of a car that sealed compartment can become a bomb - open the boot and the little switch for the boot light makes contact , gives off a spark and boom !

You can buy what is called a dc to dc charger that connects to your car battery and boost the voltage up so it will charge another battery but they are not cheap and you could set up a solar cherging system for less money .

The light globe idea will work but you really want to hook it up to the car so it will only connect the battery when the engine is running , maybe a relay activated from the ignition circuit ?

I'm guessing that the batteries are for power at the clubhouse ? Maybe time to purchase a generator ?

Hi Duncan

Not an uncommon problem with groups of people nominate some one else then you do not need to make an effort.

Clive Browns idea is sound

"Solar panels are fairly cheap these days. A reasonably sized one on the shed roof, possibly with a charge regulator, would recharge through the working week, ready for the week-end."

What do you use the batteries for and what size is the Amp Hour Rating.

Eric

https://www.towsure.com/split-charge-relay-for-towbar-electrics

All the info you need. Split chargers are fine for charging as you drive, automatically switches off so no current drawn when you start the car. You will only need a canbus system if you take the voltage from the supply at the rear lights afaik. Fitted one to a van conversion with no problems. Colin

Hi, why not just get a small generator like this **LINK** that would then save an argument as to who's turn it is to use their car.

Regards Nick.

Duncan, assuming your club can afford £120, surely the little generator in Nick,s link is the way to go. It has a 12 volt charging facility built in and gets excellent reviews, plus it gives you a 240 volt supply of course.

Just my thoughts.

Ron

It sounds like it is the electric loco battery so would be in use on the track and not available for charging during the session. Also the noise of a generator would put off visitors. An inverter generator might be quieter. Some batteries come with a small tube specifically to vent off gasses but not a real problem as cars are not pressure tight. My RR being ex police had a mounting for an extra battery in the back just connected to the main one.
I also vote for solar. Our cricket club tractor battery (as I haven't mended the dynamo) is kept alive by a tiny panel smaller than a laptop which is enough for the once a week start up of the fergie.

Thanks for all the replies.

The batteries in question are for powering the signals mainly, only 20 Ah, so only need about 2A to charge them
We've got a 5kW diesel generator which s reasonably quiet as it's in a soundproofed enclosure, but people are reluctant to have it running continuously, it would take about 10 hours to charge a battery at the recommended 1/10 of capacity
From bitter experience having a roster will not work. I've been asked in the past who'se responsibility is it to charge batteries, my response of everyone's had no effect whatever.
The long term plan is to have either a solar panel or a windmill, we've got a panel for the remote signals which works brilliantly, but it's a long hike up to the far end of the track. This was meant to be a quick fix

I've checked and the power outlet in my car is only energised when the ignition is on, but as someone pointed out would draw current from a little battery when the starter motor was running. Putting a diode in would stop the little battery getting fully charged.

Looks like I will have to advance the solar panel idea, I can't expect everyone to fit a clever system to their cars

Thanks again for your replies

Edited By Ron Laden on 01/09/2018 11:50:42

A solar panel with battery charging regulator seems a good option if you only need to charge at 2A over 10 hours. They are reasonably priced and the regulator will control overcharging and keep the battery charged.

Paul.

**LINK**

Bigger battery, solar panel is way to go. Solar would charge up during the week and leave plenty for the weekend. I have a small solar setup for a remote garage and use LED lighting for when it's dark.

Sort of on-topic - I have a non-working cordless angle-grinder which failed to switch on after 2 use cycles. The battery is fully charged, and, therefore, the assumption is that the battery protection circuit has failed.The charger works fine and the motor and output drive are undamaged and almost new. I cannot obtain a replacement protection module and don't wish to throw away an otherwise useful tool. Question - Would interposing a generic battery monitoring device between the battery and motor be sufficient protection to enable continued use or are there other problems to be considered? The item being considered is available widely at moderate (£12-15) cost. Battery working voltage is 20v

I don't have the technical knowledge or skill to manufacture anything suitable, but could, probably, manage the soldering involved.

rgds

Bill

Very late to this but to ANSWER the original question

No, that will not work.

You cannot properly charge one battery from another of the same voltage. As John F 1 has suggested you will at best end up with two partially charged batteries. Unless one battery is very discharged there will not be enough voltage difference between it and the car battery for any currrent to flow and charging to take place. If you ran the car engine then sme charging wuld happen but it's a vary expensive and poluting way of doing it. Solar panels look like the best solution.

Robert G8RPI.

Information on the grinder make and model would help. "Battery protection circuit" is a bit vague. Normally any protection is built into the removable battery. Doe the grinder have a removable battery or is it built in?

Robert G8RPI.