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-   -   12v lead-acid battery recharge (http://www.rcuniverse.com/forum/batteries-chargers-84/3568435-12v-lead-acid-battery-recharge.html)

da Rock 11-19-2005 05:41 PM

12v lead-acid battery recharge
I've got a couple of lead-acid batteries that need charging and know nothing about that type recharge.

One is the 12v 7A that powers my flight box starter and glo-plug starter. I charge that with a 500mAh wall wart.

I just now bought a HOBBICO power pack that straps under a starter so you can carry the sucker and not have that wire running to the flight box. I assumed that I could use the same 12v/500mAh wall wart charger with that, but reading the literature that come with the HOBBICO, they say to use only a 120mAh charger. The battery in the thing just says it's a 12v 1.2A lead-acid.

So is it safe to use the 500mAh charger, but only run it for a couple of hours or what? I'd really rather not have to pay for yet another wart. Jeez, I must have 30 or 40 of those things. And of course none are 120mAh.


rajul 11-19-2005 07:39 PM

RE: 12v lead-acid battery recharge
It should be fine. Your charging time for the 12V 7Ah batt can be calculated C/500 x 1.4 = 7000/500 x 1.4 = 19.6 hours.

For the 12V 1.2A batt, 1200/500 x 1.4 = 3.36 hours. However, the batt life will be better if you use around C/10 charge rate

To prevent sulphation on the battery plates keep the batt voltage above 12.4V when not in use

da Rock 11-19-2005 08:29 PM

RE: 12v lead-acid battery recharge
Thanks for the almost instant reply.

I've always wondered about how to monitor when batteries like those need to be recharged. With our ni-cads and today's smart chargers (I use a Triton nowadays), there is no problem. But with the big old lead-acids in our flight boxes etc, I've never known what to do to figure out when or how much to charge them.

Is there a way to know when and how much to charge them? For example, my 7Ah battery shows 12.67V right now. I'd assume that it won't need charging because it's nowhere near that 12.4V storage level. And I wouldn't think my ESV would even work with the sucker, and that's the only meter I own that puts a load on the test battery.

So what do you do? Just wait for the starters to seem weak? I'd rather not discover a low battery at the field. It's too long a drive to waste.

thanks again and tia on my new questions

rajul 11-19-2005 08:40 PM

RE: 12v lead-acid battery recharge
I use a DMM to monitor these things. Mine is a Sanwa CD800 which is a budget model, but is of good quality. There are also LED battery monitors for 12V batteries which indicate a low battery level. Most flight box panel also have some built-in battery indicator.

4*60 11-19-2005 09:06 PM

RE: 12v lead-acid battery recharge
As I understand it the Triton will charge lead-acid batteries. Check it out!
If so you could hook it up every time just to top up.

spritefiend 11-19-2005 09:53 PM

RE: 12v lead-acid battery recharge
you could try out a battery tender. it does it everything automatically, plug it in and the red light will turn green when its fully charged.


little bit of a price, but it will be the last charger you ever need for any lead acid, or gel cell battery. more commonly used with motorcycles, but my primary 12v battery IS a motorcycle battery :)

general info: http://batterytender.com/why_batterytender.php

da Rock 12-02-2005 09:10 PM

RE: 12v lead-acid battery recharge
Thanks for the help.

But as there always is, the answers lead to a follow up question.

I put an overnight trickle on the sucker. Next morning, I take it to fly and it works great. I wind up helping a couple of guys who can't get their engines to start. No problem. Get 'em started but after lots of cranking to find out one's needle valve is gummed solid and the other's needle valve is bent. And I help start a bunch of engines that died on the runway. And I fly until sundown. (It was an excellent day. Excellent day.)

So I got that baby sitting on the shop floor and I'm tickled how it was so convenient and.... it dawns on me. I really don't have a clue how to tell when it's in need of a charge nor how long a charge it might need. Will checking the voltage give me a clue? If there is a "it needs a charge" clue, is there also some way to tell how long a charge?

What do you guys do?

spritefiend 12-02-2005 09:25 PM

RE: 12v lead-acid battery recharge

After reaching peak 14.4 VDC, charger automatically switches to 13.2 VDC float voltage.
thats off the battery tender webpage, so id imagine thats the procedure for std. trickle chargers too.

with the battery tender jr its 100% automatic, you plug it in and when the light turns green its at its maximum charge. then again this isnt a $5 charger wall charger :)

da Rock 12-03-2005 06:38 AM

RE: 12v lead-acid battery recharge
I believe that wall warts just keep on trickling no matter what voltage the battery would have. They look like they don't have any circuitry in them at all, and I assume it'd take some circuitry to figure out start voltage, cutoff voltage and control same. And I haven't seen any "trickle chargers" that mention cutting off their trickle at some voltage. (But haven't looked real hard.)

I noticed that recommendation and figured the 14.4VDC and 13.2VDC could serve me as a parameter range. I'd consider if it was under 14.4VDC it could use some charge, the amount being how far below 14.4VDC.

I guess what I'll do is work myself out a profile. Record the VDC and charge awhile and record and charge awhile and record etc. The resulting graph ought to be useful to suggest a correlation between start voltage and required time on the wall wart.

I would think that it would be sensible, if I do try to rely on that method, that I always verify it's result. That ought to give me a clue of the accuracy of the method (when I'm just starting to use the method and the battery is new) and possibly will show me when the battery starts to lose it's capability as it ages. Is this how it's done? by any of you?

da Rock 12-03-2005 06:55 AM

RE: 12v lead-acid battery recharge
You know, I've already started doing that monitoring/recording deal and something already has shown up.

I've left the $10 trickler plugged in overnight a couple of times since I got it. The start VDC was different both times and the time on charge was different both times, but the VDC on the battery was the same both mornings. It was what would seem to me now to be "capacity" and that'd be 14.4VDC. I'm guessing that a lead acid simply stops drawing as it reaches capacity?? Further recording should tell.... or maybe one of y'all will tell before that?

JNorton 12-03-2005 06:08 PM

RE: 12v lead-acid battery recharge
A lead acid will stop drawing current when it is fully charged. Using voltage on a lead is a good indication as to the cells charge state. However don't continue to leave the charge plugged in if the voltage stays at 14.4 volts. As several people have recommended it is better to use a battery tender that puts out 12.9 to 13.4 volts - that way the battery will not continue to charge.

PipeMajor 12-04-2005 11:58 AM

RE: 12v lead-acid battery recharge
One of the "My Classic Car" episodes on the Speed Channel reviewed the Deltran Battery Tender. It was designed from the outset to charge and MAINTAIN a lead-acid battery which sees sporadic use - such as those in classic cars and/or motocycles. Batteries in these vehicles tend to sit for months at a time without being driven and having the batteries charged up.

Lead-acid batteries will sulfate when their voltage drops from non-use and pretty much ruin the battery in a short period. Using a non-automatic "trickle" charger does 2 bad things - it will S-L-O-W-L-Y charge a low battery then it will continue to charge (i.e., cook) the battery if left connected.

An automatic charger alleviates both those bad things. A properly maintained battery will last 3-5 years when maintained. A neglected battery will have a much shorter life.

I have TWO Battery tenders on my Christmas list. Hope Santa is listening...

da Rock 12-04-2005 04:54 PM

RE: 12v lead-acid battery recharge
Thank you very much. All the loose strings are tied up. All my questions answered.

Thanks and have a Merry Christmas. Hope y'all get something that needs batteries, either ni-cads or li-pos.

Flypaper 2 12-04-2005 06:21 PM

RE: 12v lead-acid battery recharge
A batt. is considered dead or in need of a charge when it reaches 12 volts. As said above the Triton is a very good charger for pb batts. Most automotive chargers charge at to high a rate for these smaller batts. and will cook them.

GoMike 12-04-2005 10:21 PM

RE: 12v lead-acid battery recharge
Like flypaper says, at 12 volts your 7AH sealed lead-acid battery is almost empty. Knowledgeable sources on this forum have determined that rested (not being charged or discharged for at least an hour or so), a DVM reading of 13 volts indicates a full charge on a lead-acid battery. A reading of 11.8 volts is almost fully discharged. It should be linear in between - i.e., 12.4 volts is about 50% charged.

I've always used the $10 500mA wall wart on mine (actually got it on sale for $5). I check it with a $3.99 DMV. My previous battery lasted about six years. The one I have now is on its third year. YMMV. I rarely check its voltage. It's not rocket science and doesn't require a lot of money for a charger or a lot of time to gain expertise. I put mine on the wall wart overnight about every second or third time I go to the field - overnight being anywhere from eight to twelve hours. I sometimes forget, but have yet to run out of juice at the field while using it to start my 40-70 size engines and fuel up my planes.


JNorton 12-05-2005 05:53 AM

RE: 12v lead-acid battery recharge

I put mine on the wall wart overnight about every second or third time I go to the field - overnight being anywhere from eight to twelve hours. I sometimes forget, but have yet to run out of juice at the field while using it to start my 40-70 size engines and fuel up my planes.
BINGO Agreed but you can't leave it hooked up 24/7 or you will cook the battery.

Rodney 12-05-2005 12:11 PM

RE: 12v lead-acid battery recharge
Be very leery of the cheaper chargers for lead/acid batteries. Unless they are truly (a very rare condition on a cheap unit) voltage limited, they will cook most of the small gell cells if you leave them on charge to long. The suggestion to use a battery keeper or a charger such as the Triton are good ones. Overcharge can be as destructive as to deep a discharge on this type of battery.

jddrumm 01-10-2006 12:55 AM

RE: 12v lead-acid battery recharge
This is kind of an old thread but I can't help it. I use the battery tender on my fishing boat. Love the thing. Never thought of useing it on my secound hobby. Will have to get a nother one for my 12v batteries.

AS-EE 01-10-2006 07:57 PM

RE: 12v lead-acid battery recharge
Just like to add that if your charger puts out 13.4v - 13.8v then you NEVER have to worry about damage to the battery because this is considered trickle or standby charge. Now if it's up there in the 14.4v - 15v range then you need to keep a watch on it.

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