Charging 24v batteries

Your logic seems fine to me.

Optimum battery voltage varies with type. I know...I ruined a gel battery by overcharging! (using a charger designed for lead acid car batteries)

I'd recomend getting on the manufacturer's (or suppliers) web site they should give accetable trickle charge rates as a current, or a maximum voltage.

I ended up building a simple 2 stage charge, basically 3 amp fast(ish) charg upto a voltage which i got from the web, then a constant voltage for trickle. I havn't ruined this new gell battery yet!

Years ago, I got hold of a document that said that trickle charge is 5% of the amp-hours of the battery. If your battery is, say, 100 amp-hours, your trickle charge would be 5 amps. I've had no problems with this "rule" so far.

With a vehicle, however, I've read that you should always crank an engine for several minutes from time to time if they're infrequently used. Not only does it keep the battery charged but it also keeps the engine lubricated and easier to start.

1/ Your logic seems fine.

2/ Since 2004 I have used solar panels to keep the batteries of my boat, trailer, camping lamps, etc.. fully charged while not in used. So far I have no problem with any of them.

The solar panel I bought is 12V - 10W, the voltage out put from the solar panel is 17V to 21V. I bought the solar panels from anrt12142005@yahoo.com

I had a 12V car battery charger that would fry 12V motorcycle batteries. The solution... Connect the charging cables to the battery with thin jumper cables with alligator clips on the ends. Worked great!!!

Your idea with the thin cables is theoretically good, but liable to catch fire in practise......

The only good battery charger is one that does not overcharge as overcharging just boils off the water (gassing) as Hydrogen & Oxygen.....which can revert to water with a loud and dangerous explosion if incorrectly vented.....

The charging current must be set correctly for the size of the battery, the battery manufacturers infos should be read.

Normal car batteries should not be allowed to have a terminal voltage of less than 12.6 volts as that is when sulphation starts....which is why some car batteries only last 2 years or so!!

Charging to a max voltage of about 13.4 volts will not 100% fill the battery, but the batteries life will be greatly extended, 2 to 4 times!!

The chargers I build for my caravan (I make a new one with new ideas about every 2nd year!) keep the batteries well within these two parameters, which is slightly over done as my battery is a leisure battery that can handle deep discharge better than normal car batteries, but of course works even better when treated well.

The current battery was bought in 2001, is well over 99% of the time connected to the charger (I did not say charging though!) and shows no age problems and has never needed topping with distilled water as of now.....

Cheap chargers should only be used for as long as it takes to charge a car battery for starting, they should then be removed. Never ever leave them charging without constantly checking the battery voltage, once it is above 13 volts, that should be more than enough to start a cars engine.....uncontrolled charging above this level just does damage.

A normal trickle charger, over time, will reduce the life of a battery. If you need to leave a charger on all the time, then you need a "smart charger" They are not cheep, maybe $150 for a 10 am 24 or 12 volt unit. You can get one that will charge two 12 v batteries and then you can have them connected is series for use if you need a 24 volt system. Check with google for "smart battery charger". I do not have the manufactur data here.

For marine use, you should use a voltage sensing charging system so as not to cook your batteries.

What's not to like about retirement

...not just for marine use, for ANY battery that you would like to last a long time!!!

Nutwood wrote: I'll probably use a electronic regulator so I can have far more exact control than your average mass produced trickle charger; but what to aim for? I've encountered commercial trickle chargers in the past that actually reduce battery life spans. It'd be nice to avoid this.

REPLY

The absorption and float voltages for 24V is exactly double that for 12V batteries. However, long term float (trickle charge) is not good. The smarter chargers today use a calendar cycle of 21 days or when voltage drops below 11.0 (22.0V) At that point they start up again and charges briefly until reaching full charge then the charger goes back to sleep. BTW its better for the battery to get a peak voltage jolt every so often rather than just maintaining a steady lower float voltage. Self discharge will gradually produce residual lead sulfation. If your float voltage is high enough to prevent sulfation formation, you risk electrolyte loss.

Sustained float voltage will cause evaporation of electrolyte in wet cells and permanent damage in sealed maintenance free batteries. Even worse for Gel or AGM. Float voltage must be derated at 27millivolt per degree F for ambient temp above 70F. So if your ambient is 80F then you derate the float voltage by 270 millivolt. 80 - 70 = 10 and 10 X 27 = 270 millivolt

Trickle charge current should not exceed 1% - 2% of Amp Hour capacity. Hence a 100 A-H start battery should not have more than 1 -2 amp trickle charge current. The 5% value someone mentioned is from way back in the dark ages of battery technology when self discharge was higher due to poor choice in plate grid material and battery design. There has been a substantial revolution in lead acid battery design in the past decade.

Why not simply use a clock timer with calendar day interval to trigger your regular charger if you don't want to spend the $150 - $200 for a real smart charger that does all this automatically.

I guess you do not value your own time as having a worth. My home hobby time is still calculated at $10 per hour to see if it's worth while for me to re-invent the wheel, or just go buy something in the store. And spend my time on something more worth while.

Elnav

The 5% value someone mentioned is from way back in the dark ages of battery technology when self discharge was higher due to poor choice in plate grid material and battery design.

That would be me, the ancient one ! You're right, that article I mentioned in my post (#2) was an old one. That was back in the early 80's I think, when NiCd batteries were common then. With the info you've given, I've become updated, however late it may be. Thanks.

Vulcan wrote: You're right, that article I mentioned in my post (#2) was an old one. That was back in the early 80's I think.

REPLY: I work with the stuff every day and even I can't keep up. The proliferation of AGM and to a lesser extent Gel Cells has created a revolution in DC power and battery applications. Really smart chargers only became possible with the development of cheap processors and switch mode power supplies that can respond to digital signal input.

Now that so many uses have huge battery banks the cost involved in replacing a cooked bank is in the thousands of dollars. A bad charger suddenly become a very expensive liability. In theory a properly charged and cycled battery wil deliver 10 years of life. So why do so many people have to replace them after three years?

Elnav

You're lucky. Not all chargers can be connected together, in series or parallel. Get a 24V charger or connect 12V to each battery.

For permanent solution, get a good 24V charger and plug the bulldozer in when parked. A good battery should hold charge for more then a month. So a charger with timer or auto shut off/on depends on battery charge would be best. Now DO NOT connect any electronic charger together. Especially those use pulse width modulation. They'll fight to control the pulse.

Pineapple

Nutwood wrote: Recently we had a small problem with a bulldozer (used infrequently) that wouldn't crank. Charging of batteries was required."

New reply. There is a product which is designed to solve exactly that kind of problem and situation. The product is made by Pulsetech www.pulsetech.com One of their models is solar powered. Logging companies and seasonal equipment operators can safely leave a piece of equipment siting in the wilds and return next year and expect the equipment will start and run from the existing battery. Cost of this device is around $100 retail and often sell for less. I have been using these for six years now and not a single customer has ever had a repeat problem after I install these. I left a diesel truck sitting unused for six months last winter. It started first try. Had enough juice to run the glow plugs for 30 seconds and crank the engine at a fast clip. Better than a plug-in charger which requires utility power to work.

Elnav

Thank you all for your replies. I'm going to investigate further the smart charger option. I've always had my doubts about the float charge method. I too have heard the 5% value but it's obviously too high. With a pair of 150 A/h batteries that's 180 watts going somewhere and it can't be a good thing. Even 1% is quite a bit viewed 24/7.

The solar arrangement sounds good, definitely worth further investgation. I'm certainly not going to waste time reinventing the wheel but a constant voltage or current source can be knocked up very quickly for a few $'s. If that'd fit the bill I'd do it, however with the cyclic timing arrangement it would be harder to compete with a commercial product. I thought perhaps that it would be possible to put a figure on the internal discharge and just keep putting that much back in.

On item 1, provided the 12V side of the chargers were isolated from earth, and from each other, it wouldn't matter in principle whether the chargers were connected across each battery or whether they were connected in series at 24V. A preference would be for the former arrangement, so that any electronics in each 12V circuit didn't respond to the electronics of the other as the battery voltages approach the supply voltages as charging approaches completion.