Testing gel cells

[mike]

On 7/22/2014 10:00 AM, Jeff Liebermann wrote:

On Mon, 21 Jul 2014 14:31:25 -0700, mike <ham789@netzero.net> wrote:

On 7/21/2014 12:36 PM, mc@uga.edu wrote:
On Monday, July 21, 2014 1:51:02 PM UTC-4, David Platt wrote:
http://www.westmountainradio.com/cba.php

Thanks, looks promising; actually I might make such a thing myself.

I have a programmable power supply and programmable load fixture.
I've messed around with NiCd, NiMH, Lithium, Lead batteries.

The most consistent/useful metric seems to be the internal series resistance
of the cells...except for the obvious case where a shorted cell has
low ISR ;-)

Also, the battery temperature has a huge effect on the ESR. I prefer
the discharge curve mostly because I don't believe in a single number
can totally describe the battery SOH (state of health).

As for building a discharge battery tester:
http://www.foobert.com/blog/2009/11/08/arduino-battery-capacity/comment-page-1/

There are plenty of commercial discharge testers:
https://www.google.com/search?q=battery+discharge+tester&tbm=isch
but the West Mtn Radio CBA series seems to give the most useful
results. However, the design does have a problem. It doesn't use a 4
terminal Kelvin connection for the leads. In the CBA-II, the battery
voltage is measured at the tester, not at the battery terminals. If
there is any voltage drop in the leads or the battery terminal
connections, the voltage drop is going to mangle the graphs. It's not
a problem at low discharge currents, but at the high currents expected
from a gel cell, it will be a problem. I looked into modifying mine.
I think it can be done but not easily, so I decided not to risk it.

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.

 

[Michael A. Terrell]

dave wrote:

Isn't the proper tech term AGM batteries?

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.

 

On Monday, July 21, 2014 11:34:43 AM UTC-4, m...@uga.edu wrote:
> Any thoughts about the best way to test a lead-acid gel cell? I am plotting the construction of a device that will discharge them to 11 V with a constant load and record the time it takes. Does anybody make that gadget commercially at low cost? Any shortcuts? Does testing under load tell you much?

I used to find my 12V 7's dead in my truck when I went to use them on a service call. I no longer keep batteries in stock anymore as I consider them to be a "perishable" item. However if you must keep gel cells in your vehicle you could build a little constant current charger out of an LM317T. (I thought about doing this but realized that I really didn't need to keep batteries in the truck anymore). Then you'd have a constant current trickle charge to your batteries in your vehicle any time the engine is running. I think the LM317T will handle up to an amp, (with a sufficient heat sink). However in the case of a 12V 7 I would think you'd want much less. I've been trickle charging one of these batteries at 10ma in my home brew alarm system for the past 9 years and it's still functioning. Another thing is with a constant current supply like an LM317T ahead of the battery the series diode would also not be necessary. Lenny

 

[mike]

On 7/23/2014 4:39 AM, captainvideo462009@gmail.com wrote:

On Monday, July 21, 2014 11:34:43 AM UTC-4, m...@uga.edu wrote:
Any thoughts about the best way to test a lead-acid gel cell? I am plotting the construction of a device that will discharge them to 11 V with a constant load and record the time it takes. Does anybody make that gadget commercially at low cost? Any shortcuts? Does testing under load tell you much?

I used to find my 12V 7's dead in my truck when I went to use them on a service call. I no longer keep batteries in stock anymore as I consider them to be a "perishable" item. However if you must keep gel cells in your vehicle you could build a little constant current charger out of an LM317T. (I thought about doing this but realized that I really didn't need to keep batteries in the truck anymore). Then you'd have a constant current trickle charge to your batteries in your vehicle any time the engine is running. I think the LM317T will handle up to an amp, (with a sufficient heat sink). However in the case of a 12V 7 I would think you'd want much less. I've been trickle charging one of these batteries at 10ma in my home brew alarm system for the past 9 years and it's still functioning. Another thing is with a constant current supply like an LM317T ahead of the battery the series diode would 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.

 

[dave]

On 07/22/2014 07:41 PM, Michael A. Terrell wrote:

dave wrote:

Isn't the proper tech term AGM batteries?


Only for AGM batteries. Not all gel cells have a glass mat.


Thyanks

 

[Michael A. Terrell]

captainvideo462009@gmail.com wrote:

On Monday, July 21, 2014 11:34:43 AM UTC-4, m...@uga.edu wrote:
Any thoughts about the best way to test a lead-acid gel cell? I am plotting the construction of a device that will discharge them to 11 V with a constant load and record the time it takes. Does anybody make that gadget commercially at low cost? Any shortcuts? Does testing under load tell you much?

I used to find my 12V 7's dead in my truck when I went to use them on a service call. I no longer keep batteries in stock anymore as I consider them to be a "perishable" item. However if you must keep gel cells in your vehicle you could build a little constant current charger out of an LM317T. (I thought about doing this but realized that I really didn't need to keep batteries in the truck anymore). Then you'd have a constant current trickle charge to your batteries in your vehicle any time the engine is running. I think the LM317T will handle up to an amp, (with a sufficient heat sink). However in the case of a 12V 7 I would think you'd want much less. I've been trickle charging one of these batteries at 10ma in my home brew alarm system for the past 9 years and it's still functioning. Another thing is with a constant current supply like an LM317T ahead of the battery the series diode would also not be necessary. Lenny

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.

 

[Cydrome Leader]

Jeff Liebermann <jeffl@cruzio.com> wrote:

On Mon, 21 Jul 2014 09:12:58 -0700 (PDT), mc@uga.edu wrote:

Thanks. Yes, a dead or severely weakened battery is
easy to spot,

Actually, it's not easy. I've been fooled too often. In my never
humble opinion, the only way to do it right is with a controlled
discharge test and comparing it with a known good battery. There's
quite a bit of variation in the curves depending on discharge rate,
battery quality, and thermal management making interpretation and
analysis difficult. I've found that the only way to be really sure is
with a comparison. Sure, a dead battery is easy to spot, but trying
to predict how long it will last, whether it should be replaced, and
how much life is left, are not easy. That's why large organizations
do not test and replace UPS batteries on a fixed schedule.

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.

 

[Jeff Liebermann]

On Mon, 28 Jul 2014 03:04:01 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote:
On Mon, 21 Jul 2014 09:12:58 -0700 (PDT), mc@uga.edu wrote:

Thanks. Yes, a dead or severely weakened battery is
easy to spot,

Actually, it's not easy. I've been fooled too often. In my never
humble opinion, the only way to do it right is with a controlled
discharge test and comparing it with a known good battery. There's
quite a bit of variation in the curves depending on discharge rate,
battery quality, and thermal management making interpretation and
analysis difficult. I've found that the only way to be really sure is
with a comparison. Sure, a dead battery is easy to spot, but trying
to predict how long it will last, whether it should be replaced, and
how much life is left, are not easy. That's why large organizations
do not test and replace UPS batteries on a fixed schedule.

If you mean they Do have a maintenance schedule, yeah, you need to do that
with large strings of batteries.

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.

But it's the same for anything where
reliability is important- you do lots of preventative maintenance.

Yep.

The exception to this rule would be bridges. in the US, we just let them
collapse, then figure it out later.

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:
<http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries>
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

 

[Cydrome Leader]

Jeff Liebermann <jeffl@cruzio.com> wrote:

On Mon, 28 Jul 2014 03:04:01 +0000 (UTC), Cydrome Leader
presence@MUNGEpanix.com> wrote:

Jeff Liebermann <jeffl@cruzio.com> wrote:
On Mon, 21 Jul 2014 09:12:58 -0700 (PDT), mc@uga.edu wrote:

Thanks. Yes, a dead or severely weakened battery is
easy to spot,

Actually, it's not easy. I've been fooled too often. In my never
humble opinion, the only way to do it right is with a controlled
discharge test and comparing it with a known good battery. There's
quite a bit of variation in the curves depending on discharge rate,
battery quality, and thermal management making interpretation and
analysis difficult. I've found that the only way to be really sure is
with a comparison. Sure, a dead battery is easy to spot, but trying
to predict how long it will last, whether it should be replaced, and
how much life is left, are not easy. That's why large organizations
do not test and replace UPS batteries on a fixed schedule.

If you mean they Do have a maintenance schedule, yeah, you need to do that
with large strings of batteries.

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.

But it's the same for anything where
reliability is important- you do lots of preventative maintenance.

Yep.

The exception to this rule would be bridges. in the US, we just let them
collapse, then figure it out later.

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:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
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.

Ha!