Battery float or maintence charging

[3v0]

I am thinking about what I need to maintain my lawn tractor battery over the winter. I know I could just charge it every month or two but I am more interested in something I can hook on and forget. I know you can get float chargers but they seem to be a one size fits all and the little battery is much smaller capacity so a float charger could well over charge it. And I want to tinker with this.

Would it be better to keep the battery at a fixed voltage or to let voltage drop off a bit then top off the charge.

How do you feel about using pulses? There are mixed messages on this. My thinking is that as long as it does not harm the battery why not use it to help prevent sulphation.

We also have a towncar that is only used on out of town trips so it would benefit from a similar setup.

 

[Ian Rogers]

My business partner goes on holiday to America for months at a time ( semi retired ) he bought a "Battery tender" its a tiny charger. it was only £6. Now he can start his car when he gets back.. There are many different ones.

 

[Nigel Goodwin]

You just need to trickle charge it - a simple transformer, rectifier, and current limiting resistor is all you need - 100mA would probably be enough current?.

As Ian says, such devices are commercially available at little cost.

 

[Brevor]

Hi 3V0,
I had the same problem with my lawn tractor. I bought a battery maintainer at WalMart for $19.95 about 5 years ago and it's worked fine ever since then.

 

[3v0]

I was rather interested in playing with building one. I know you can buy them but what is the fun in that.

 

[Nigel Goodwin]

I was rather interested in playing with building one. I know you can buy them but what is the fun in that.

Then refer to post #3

 

[4pyros]

You could look into battery desulfator circuits.

 

[jpanhalt]

Have I got a deal for you. This device (https://www.electro-tech-online.com/threads/chinese-or-japanese-translaton.129013/) is apparently a self-powered desulfator. That is, it requires no outside power to perform its magic. If you (3v0) promise to use it for at least a year, I will send it to you for no charge, shipping included.

On the other hand, if you want your garden tractor battery to last until next year, I would completely disconnect it from the circuit and either periodically charge it or trickle charge it. My full-size batteries (tractor, Summer car) work just fine when charged and allowed to sit the Winter with no additional charging, but of course, their AH rating is quite a bit more than that of a smaller lawn tractor battery. Cleveland Winters are longer than Oklahoma ones.

John

 

[3v0]

That is very kind but no thanks.

I wanted something to putter around with that was not a long term project. Buying of getting one as a gift does not help with that. But thanks for the other thread.

I fully understand why people are saying to buy one. I have offered that advice to a lot of people wanting to build stuff to save money. That is not the case here. Just want to play in the sandbox. See where it goes.

 

[jpanhalt]

If you bite on the desulfator plan, how about adding some science. It should really be quite easy.

1) All of the sulfate comes from the battery electrolyte.
2) A new battery that has been "completely discharged" or sulfated (theory) will have almost pure water as its electrolyte.
3) A desulfator that actually works would add sulfuric to the electrolyte.

Now, you can't easily tell how much sulfuric acid is produced by pH, but you can with a little chemistry. Take a battery that is highly, but not completely sulfated. Fully charge it. I would charge it, then trickle charge it for several days. Then, charge it again to get a little gassing.

Now, measure the sulfuric acid and soluble sulfate concentration. Titration with base is one way. Ba(OH)2 precipitation of all sulfate is another.

Now, attach the desulfator. When it is done, check to see if the amount of sulfuric acid has increased. If the things really worked, you should see a huge increase in sulfuric acid concentration from a battery that is 25% to 50% sulfated. That, of course, doesn't prove that the battery capacity has increased, but it would answer at least part of the question. You need to be sure that the volume of electrolyte doesn't change in the process.

John

 

[k7elp60]

i have a circuit that I designed that uses a LM317T, it is adjustable in voltage and the current limiting is also adjustable. I also use a TL431 and a LM358 to monitor charging current and turn on an LED when the charging current drops to a adjustable level. If you are interested I would be happy to post the schematic and details.
Ned

 

[3v0]

I would like to see your schematic k7elp60.

jpanhalt, wouldn't the specific gravity meter used to check charge work in place of Titration?

 

[jpanhalt]

Re: specific gravity

That would probably work too, if precise enough.

The total battery weight should not change, and that would be another variable that could be measured. However, the apparent volume of electrolyte might change, depending on the density of the precipitates and electrolyte fluid.

John

 

[k7elp60]

Here is the schematic. D2 is in the circuit in case the AC power is off so that the battery doesent discharge thru the charger parts. The voltage across the 1N4007 varies with current and the so the output of the charger is adjusted by R4 with a load of approximately 200 Ω. In this case battery capacity AH/100 (70mA) for a 12V 7AH battery. The 1N4007 also drops some of the voltage so it lessens the heat dissipation of the LM317. Increasing the size of the heatsink for the LM317 offsets this and a 1N5819 diode could also be used. I use a AC/DC adapter that supplys close to 18V@ 500mA(Such as Jameco #163272)
The 1.5Ω resistor limits the full charge current. With the value shown the current limit is near 470mA. The LM358 circuitry is used to detect when the charge current drops to the AH/100 level, this indicates charged.
NED

 

[mvs sarma]

Burkhard Kainka, a Gernam, came up with a battery maintainer ( a sort of de-sulphator) with no ecternal unit needed. it was like a short timed pulse of 1 or 2 amps into load for a millisec., and once in few hours. Aper him it doesnt allow the battery die . this is publishd as an element in elektor 201-Jul/Aug issue on page 60 of uk edition.

 

[3v0]

Thanks for all the good info and A quick update.

I picked up a couple of the harbor freight float chargers. Multimeter says the current is 430mA or so. Given that tractor/motorcycle type batteries should not be charged over 1.5A it may be too much for a float charge which is what I was thinking when I started this thread. But still should be good for the cars and maybe a starting point for something better.

I am going to leave it hooked to the old battery for a while to see what it does. I had been using a bench supply with nice DC. I expect these floats are rectified AC without smoothing so the pulsing may be helpful.

 

[mvs sarma]

i suppose, float charging is at a constant voltage and thus the current, though shown at 430mA, would come down in 30 mnts or so after connection.

 

[3v0]

You are indeed correct sarma. It has.

 

[4pyros]

I picked up a couple of the harbor freight float chargers.

Last time I tryed the Harbor Freight chargers the two of them where reading way differant voltages and current.
Cheak your two to see how close to each other thay are.

 

[3v0]

WIll do and get back with the info.