I've used two methods. Short the leads to measure the resistance and subtract it out with math. Turn off the current when measuring the voltage.
For NiMH and NiCd cells, the shape of the charge curve is more useful than the actual voltage.
There's also diminishing returns. With the computer, power supply, load fixture running, I figger it costs alsmost as much in juice to power the stuff than it take to buy an alkaline AA cell to replace the NiCd one I'm charging.
Only for AGM batteries. Not all gel cells have a glass mat.
-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
ing the construction of a device that will discharge them to 11 V with a co nstant load and record the time it takes. Does anybody make that gadget co mmercially at low cost? Any shortcuts? Does testing under load tell you m uch?
I used to find my 12V 7's dead in my truck when I went to use them on a ser vice call. I no longer keep batteries in stock anymore as I consider them t o be a "perishable" item. However if you must keep gel cells in your vehicl e you could build a little constant current charger out of an LM317T. (I th ought about doing this but realized that I really didn't need to keep batte ries in the truck anymore). Then you'd have a constant current trickle char ge to your batteries in your vehicle any time the engine is running. I thin k the LM317T will handle up to an amp, (with a sufficient heat sink). Howev er in the case of a 12V 7 I would think you'd want much less. I've been tri ckle charging one of these batteries at 10ma in my home brew alarm system f or the past 9 years and it's still functioning. Another thing is with a con stant current supply like an LM317T ahead of the battery the series diode w ould also not be necessary. Lenny
I'd like to see the circuit. I've never been able to figger out how to charge a 12V battery from 12V with a LM317 current supply in the middle and support the required headrooms.
If you need low current with low headroom, an incandescent light bulb works great for trickle charging batteries.
Thyanks
A Schottky diode and a resistor to give the desired current is all you need. The 12 volt system in your truck wouldn't give you enough output with a LM317. :)
-- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
If you mean they Do have a maintenance schedule, yeah, you need to do that with large strings of batteries. But it's the same for anything where reliability is important- you do lots of preventative maintenance.
The exception to this rule would be bridges. in the US, we just let them collapse, then figure it out later.
Yes. That's what I meant. Sorry about the lousy English. I get my supply of half dead gel and AGM batteries from various companies that replace them on a set schedule, and never test them.
Yep.
I think I've mentioned this story before, but it's worth repeating. It concern NiMH and NiCd batteries instead of gel cells, but the principal is the same. The county has a local HEAR (Hospital Emergency something Radio) network. Every hospital, convalescent hospital, and medical emergency facility in the area was issued Motorola HT2000 handheld radios, a desktop battery charger, instructions, and nothing else. No spare batteries. The radios were left in the charger 24x7. 1-2 years later, all the batteries were dead.
Once a week, everyone was expected to check into an emergency preparedness net. This actually worked because even dead batteries have enough life in them to operate out of the charger for a few minutes. So, nobody noticed that the batteries were dead or dying.
At the time, I was working at two convalescent hospitals. I was working on a computer when it was time for the net. I heard the characteristic screech of the dead battery alarm from the radio after the first ID transmission. Oh-oh... dead battery. A quick check of the radio confirmed my suspicion. I later checked other radios, and found a similar situation.
I emailed the local emergency coordinator with the bad news, who ignored me because I wasn't in a box on his organizational chart. So, I passed the ball to one of the ARES members, who reluctantly gave him the bad news and suggested purchasing some new batteries. That was done immediately, followed by the retirement of the emergency coordinator.
His replacement was considerably more interested in the problem, but electronically clueless. I told her that the batteries need to be regularly replaced, that there should be a spare battery available for rotation, and that a means of charging the spare indpendently from
117vAC or 12vDC should be available. All what happened was that new batteries were issued. After about 2 years, those batteries were also dead, and I had to repeat the entire exercise. I gave up.The radios were recently replaced by the latest greatest narrow band versions, which use Li-Ion batteries. They're designed to be left in the charger. However, Li-Ion batteries tend to deteriorate if left at
100% charge and run hot: My guess is about 2-3 years before we experience another repeat performance.I asked if the county radio service shop has a battery discharge tester. Nope.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
Ha!
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.