Testing gel cells

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?

 

[Cydrome Leader]

mc@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?

Just toss a car headlamp on it and check back every 15 minutes or
whatever.

Really, when was the last time anybody said "Whoah, I had no idea that
battery was not working, I was fooled the entire time, even though it
wasn't charging or discharging correctly!" A bad battery is pretty east to
spot.

 

Thanks. Yes, a dead or severely weakened battery is easy to spot, but I would also like to catch less severe deterioration that would give less-than-expected battery life in the field. (I'm no longer talking about UPSes here, but rather, batteries for portable scientific equipment.)

 

Thanks again! An 11-volt Li-ion system would not power my astronomy equipment properly. I do OK with gel cells but need to know, before going out in the field, that they are in good shape.

BTW, any thoughts on maintaining a gel cell by keeping it attached to a car's electrical system? What should I put in between? The car runs at 13.9 volts, which is a little high for float-charging a gel cell.

 

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.

 

[Jeff Liebermann]

On Mon, 21 Jul 2014 08:34:43 -0700 (PDT), mc@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?

See my comments in resonse to your original question.

Also, for SMALL gel cells, I use a West Mountain Radio CBA-II to test
batteries:
<http://802.11junk.com/jeffl/NiMH/cba-II.jpg>
<http://www.westmountainradio.com/cba.php>
The typical 12v 7A-hr UPS battery is about the limit of what I want to
try with a discharge test. The heat sink gets rather hot and the fan
works overtime.

--
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

 

[Jeff Liebermann]

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.

but I would also like to catch less severe deterioration that would
give less-than-expected battery life in the field. (I'm no longer
talking about UPSes here, but rather, batteries for portable
scientific equipment.)

That's what the CBA-II and similar discharge testers will give you.
Such testing is common in the RC (radio control) groups.

Incidentally, when you buy SLA, gel, or AGM batteries, look at the
weight. The better batteries will have more lead and therefore weigh
more. The cheap junk that doesn't last more than a few
charge-discharge cycles will weigh less.

You might look at Li-Ion replacement batteries for UPS's.
<http://www.batteryspace.com/li-ion-battery-packs-to-replace-lead-acid.aspx>
I've only done one, about a year ago, so it's too soon to tell if it
will survive. So far, no surprises. However, I cheated. I disarmed
the charging circuit, and replaced it with a balance charger borrowed
from the RC crowd:
<http://www.hobbyking.com/hobbycity/store/RC_PRODUCT_SEARCH.asp?strSearch=balance+charger>
A balance charger charges each 3.7v cell individually. Another catch
is that the nominal voltage is 11.1v, not 13.6v.

--
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

 

[David Platt]

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?

http://www.westmountainradio.com/cba.php

 

[mike]

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 ;-)

 

[John Robertson]

On 07/21/2014 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've played around with using Bob Parker's ESR meter kit for testing
batteries - the results appear to be significant, but of little use in
our shop as we don't deal much with rechargeable battery products (like
forklifts, etc.).

Notes here:

http://flippers.com/esrkthnt.html (near bottom of the page).

If anyone has readings to add to the page please send to me so I can
expand it a bit...

John :-#)#

--
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

 

[dave]

On 07/21/2014 09:12 AM, mc@uga.edu wrote:

Thanks. Yes, a dead or severely weakened battery is easy to spot, but I would also like to catch less severe deterioration that would give less-than-expected battery life in the field. (I'm no longer talking about UPSes here, but rather, batteries for portable scientific equipment.)

Isn't the proper tech term AGM batteries?

 

[dave]

On 07/21/2014 09:39 AM, Jeff Liebermann 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.

but I would also like to catch less severe deterioration that would
give less-than-expected battery life in the field. (I'm no longer
talking about UPSes here, but rather, batteries for portable
scientific equipment.)

That's what the CBA-II and similar discharge testers will give you.
Such testing is common in the RC (radio control) groups.

Incidentally, when you buy SLA, gel, or AGM batteries, look at the
weight. The better batteries will have more lead and therefore weigh
more. The cheap junk that doesn't last more than a few
charge-discharge cycles will weigh less.

You might look at Li-Ion replacement batteries for UPS's.
http://www.batteryspace.com/li-ion-battery-packs-to-replace-lead-acid.aspx
I've only done one, about a year ago, so it's too soon to tell if it
will survive. So far, no surprises. However, I cheated. I disarmed
the charging circuit, and replaced it with a balance charger borrowed
from the RC crowd:
http://www.hobbyking.com/hobbycity/store/RC_PRODUCT_SEARCH.asp?strSearch=balance+charger
A balance charger charges each 3.7v cell individually. Another catch
is that the nominal voltage is 11.1v, not 13.6v.

We have a Harley with a 13.6VDC Li Ion battery. It has a maintenance
charger with current for each cell. Shorai brand. Very light.

 

[dave]

On 07/21/2014 09:44 AM, mc@uga.edu wrote:

Thanks again! An 11-volt Li-ion system would not power my astronomy equipment properly. I do OK with gel cells but need to know, before going out in the field, that they are in good shape.

BTW, any thoughts on maintaining a gel cell by keeping it attached to a car's electrical system? What should I put in between? The car runs at 13.9 volts, which is a little high for float-charging a gel cell.

Not that high. Automotive electronics run on 13.6 VDC. A lead acid
battery is about 2.2VDC per cell.

 

mc@uga.edu wrote:

BTW, any thoughts on maintaining a gel cell by keeping it attached to
a car's electrical system?

I have recharged a 12 V, 7 Ah gel cell by connecting it to a car
cigarette lighter socket while I was driving, and it seemed to work OK.
I just did it for a couple of hours on a couple of trips - I didn't
leave the gel cell battery connected to the car as a regular thing.

> What should I put in between?

You might want to put in a diode, to ensure that the gel cell doesn't
try to supply the car's electrical system if the car's voltage drops
for some reason. Something like a 1N5822 is good for 3 amps of current
and will only drop about half a volt. The diode should "point at" the
gel cell.

If you really don't like losing 0.5 V in the diode, you could wire in an
automotive relay between the gel cell and the car. The contacts connect
the gel cell to the car, and the coil is wired to the hot-in-run wire
from the ignition switch. That way, the gel cell only charges when the
key is on. You'll still lose a little in the relay, but much less, like
0.1 V or so.

The car runs at 13.9 volts, which is a little high for float-charging
a gel cell.

Power-Sonic wants to use 13.50 to 13.80 V for float charging their
batteries, so you're not that far off. On the other hand, your car's
electrical system can be anything from about maybe 9 V (running the
starter) to 15 V (cruising down the Interstate on a sunny day).

*If you can find one surplus*, you could use a DC-DC converter "brick"
to float charge a gel cell. The ones you want have an input voltage
range of 9 to 18 V DC (or wider), and output a constant DC voltage. A
couple of problems: lots of these output 12.0 V exactly and don't have
a way to adjust the output voltage up or down. Some are adjustable,
though. Also, if you buy these new, they are really expensive for some
reason - once you get over a couple of dozen bucks, you're probably
better off buying a real official charge controller like Jeff Liebermann
posted.

Sometimes you can find power supplies that are meant to run laptops in
a car. These often have a switchable output from about 12 to 20 V or
so. You can set the output to maybe 14 V and use a diode in series with
the output to get rid of another 0.3 V and have a fairly constant
voltage to charge your battery with. Again, finding a surplus or
closeout might help. A few years back, Rat Shock was closing out a
40 or 60 W version of one of these for $10, when it had sold new for
$50+.

It's sort of an offense against thermodynamics, but you could also use
a 12 V DC to 120 V AC inverter, and then a regulated, switching "wall
wart" DC supply to provide a constant voltage to charge the battery.
You could even use a real official gel cell charger - these are
basically wall warts with $1 extra in components, but they sell for 3
times the price. If you are doing stuff "in the field", you probably
already own the DC-to-AC inverter, and if you luck into a wall wart
with the right output voltage, this can be an inexpensive option.

Matt Roberds

 

[Jeff Liebermann]

On Mon, 21 Jul 2014 09:44:09 -0700 (PDT), mc@uga.edu wrote:

An 11-volt Li-ion system would not power my astronomy
equipment properly. I do OK with gel cells but need to know,
before going out in the field, that they are in good shape.

If your unspecified astronomy equipment is that critical, you're going
to have problems with any type of unregulated power source. You might
want to investigate what device is crapping out at low voltages and do
something to compensate.

BTW, any thoughts on maintaining a gel cell by keeping it attached
to a car's electrical system? What should I put in between?
The car runs at 13.9 volts, which is a little high for float-charging
a gel cell.

It's called a "charge controller". For charging from 12v, the RC
(radio control) crows has the best stuff. This is typical:
<http://hobbyking.com/hobbyking/store/__6792__iCharger_106B_plus_250W_6s_Balance_Charger.html>
<http://www.hobbyking.com/hobbyking/store/HK_movies2.asp?idmovie=4109e00880164d93bc383f6b5322ee44>
I suggest you watch the video (10min). 10-18v input. It will charge
almost any type of small battery, including 1 to 12 lead-acid cells
(at 2v each). Programming is ugly but once saves in memory, you're
done. This is probably overkill for a gel cel but will be handy when
you give up on gel cells and switch to Li-Ion. Note that this model
will measure the battery ESR.

--
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

 

[Jeff Liebermann]

On Tue, 22 Jul 2014 05:36:48 -0700, dave <ricketzz@earthlink.net>
wrote:

We have a Harley with a 13.6VDC Li Ion battery. It has a maintenance
charger with current for each cell. Shorai brand. Very light.

What voltages do you normally measure across its terminals? I've seen
various schemes used to get 13.6v. Some are lazy and just deliver
11.1v while claiming 13.6v. Some have a built in PWM (pulse with
modulator) that acts as a voltage regulator to deliver the 13.6v. Some
use 4 cells at 14.8v that barely reached full charge because that
would require about 16.8v charging voltage. Hopefully, your also has
short circuit protection.

--
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

 

[William Sommerwerck]

"Jeff Liebermann" wrote in message
news:8t3ts99jplecgrr9r1a7nd6tl441og7rfo@4ax.com...

It's called a "charge controller". For charging from 12V,
the RC (radio control) crows has [sic] the best stuff.

Are they the ones who taught Dumbo how to fly?

 

[Jeff Liebermann]

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.



--
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

 

[Jeff Liebermann]

On Tue, 22 Jul 2014 09:50:07 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net> wrote:

"Jeff Liebermann" wrote in message
news:8t3ts99jplecgrr9r1a7nd6tl441og7rfo@4ax.com...

It's called a "charge controller". For charging from 12V,
the RC (radio control) crows has [sic] the best stuff.

Are they the ones who taught Dumbo how to fly?

No. Dumbo will fly without the help of RC or crows?
<http://amazingpics.net/content/Creative%20Pics/SkyDumbo.jpg>

Crows? Did I write that or was that my spelling chequer? It should
be "crowd".

--
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

 

[David Platt]

In article <koGdnSg9yJPLx1POnZ2dnUVZ_vKdnZ2d@earthlink.com>,
dave <dave@dave.dave> wrote:

>Isn't the proper tech term AGM batteries?

As I understand it, "gel cell" != "AGM".

Again, as I understand it, a true "gel cell" uses an electrolyte which
contains a gelling agent. It's one step away from a flooded-cell
battery; the gel keeps the electrolyte from spilling out if the
battery is operated in a non-upright position. Think it it as a
Jello-based battery

"AGM" = "Absorbed glass mat". It's a form of "starved electrolyte"
cell, in which a smaller amount of a more-concentrated electrolyte is
soaked into a fiberglass separator mat located between the plates. As
with a gel cell, there's little or no free-flowing liquid to spill
out, but the mechanism used to control the electrolyte position is
different.

It wouldn't surprise me if a lot of what people refer to as "gel
cells" (e.g. the rectangular batteries for UPS applications) are
actually being manufactured using AGM designs these days.