Battery Discharger?

[William P. N. Smith]

I'm looking for a battery discharger for testing my golf cart
batteries for capacity. Golf cart and charger companies make them for
on the order of $500, but it's just a (resistive?) load, a low voltage
disconnect, and a clock to give runtime, so I can't imagine that there
isn't a far less expensive one available that I just don't know about.

Anyone have any sources for this kind of thing for less than the cost
of a new set of batteries? 8*|

Thanks!

 

[Richard P.]

Kind of low tech but I know a guy who used a car headlight and a Trace C-30 (???) and used the LVD
feature.

 

[William P. N. Smith]

I doubt a discharger is going
to do much to tell you how much capacity you have, as far as drive time, in
a golf cart

The golf cart industry uses a standard 75-amp current drain, so
batteries can be tested and compared using a common specification.
I'd really like to have taken measurements when the carts were new, so
I can compare to what they are now, and schedule battery replacement
for convenient times.

I'd take the batteries to a mechanic and have him test them.

Our local mechanic doesn't have the discharge tester either, and
specific gravity tests show the batteries to be in fine shape when
fully charged, they just don't seem to last as long as they did when
new.

I suppose I could build something, anyone have any thoughts about 75A,
{36,48}V loads?

Thanks!

 

[Ecnerwal]

Anyone have any sources for this kind of thing for less than the cost
of a new set of batteries? 8*|

Feel like cobbling? Various RE equipment you may already own will do the
LVD function, or you can do it with a comparator, some sort of voltage
reference, and a solid state relay (or a comparator and some solid state
stuff to drive a mechanical relay). $20-50

For the clock, I expect the easiest solution would be a voltage
regulator to pull 16-11 volts (or is this 6 to test the individual
3-cell batteries? Does not matter, same thing works) down to 1.5 volts,
and feed that into a typical cheap quartz clock that takes a 1.5 volt
battery. $2, perhaps $5 if you can't find the clock for free.

Load - all sorts of stuff works - light bulbs, heating elements, etc.
$0-$20 ought to do it. Junk toasters and hairdryers are handy sources of
Nichrome wire.

So you should be out well under $100, if all you need is to get a time
on dumping into a resistive load until LVD.

Whether you are in your New England or Caribbean locale will probably
affect how easily the electronics parts can be had. Of course, if you
are hard up for parts, you, a voltmeter, a watch (and perhaps a stereo
along with the other load to help pass the time) will get the job done.
Probably best to save the beer or rum & cokes until after the job is
done, though.

 

[wmbjk]

I'm looking for a battery discharger for testing my golf cart
batteries for capacity. Golf cart and charger companies make them for
on the order of $500, but it's just a (resistive?) load, a low voltage
disconnect, and a clock to give runtime, so I can't imagine that there
isn't a far less expensive one available that I just don't know about.

Anyone have any sources for this kind of thing for less than the cost
of a new set of batteries? 8*|

Thanks!

This would be a much more limited alternative to the sweet-sounding
$500 solution, but the price is right.

Step 1. Build a strong bookcase for your bathroom.
Step 2. Load one month's supply of Harbor Freight catalogs.
Step 3. Use any time left over to check for sale prices on these
items. I think I remember $9.99 making an appearance.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=6317
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90920
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90636
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=90893

Wayne

 

[William P. N. Smith]

Feel like cobbling? Various RE equipment you may already own will do the
LVD function, or you can do it with a comparator, some sort of voltage
reference, and a solid state relay (or a comparator and some solid state
stuff to drive a mechanical relay). $20-50

Yeah, I'm beginning to think that kludging something together is the
way to go. Will a solid-state relay drop out DC voltages, or are they
(still) triac or SCR-based, and will stick on?

Of course, now my brain wants a net-metering solution, so I can dump
the power back into the grid, instead of wasting $3-5 worth of power
heating up a resistor... 8*)

 

[William P. N. Smith]

Step 3. Use any time left over to check for sale prices on these
items. I think I remember $9.99 making an appearance.
http://www.harborfreight.com [...]

I've really got to pay more attention to Harbor Frieght! I'd need 3
or four of these things in series to test my {36,48}V golf carts, but
that's easy enough. Anyone played with one of these things enough to
know how warm it gets, or it it ought to have a fan for cooling?

Thanks for the thoughts guys!

 

[Anthony Matonak]

Step 3. Use any time left over to check for sale prices on these
items. I think I remember $9.99 making an appearance.
http://www.harborfreight.com [...]

I've really got to pay more attention to Harbor Frieght! I'd need 3
or four of these things in series to test my {36,48}V golf carts, but
that's easy enough. Anyone played with one of these things enough to
know how warm it gets, or it it ought to have a fan for cooling?

I think the idea is to test the batteries one at a time.
It's likely the batteries in your golf carts are really
6V or 12V and you would only need one of these units.

Anthony

 

[Vaughn Simon]

I've really got to pay more attention to Harbor Frieght! I'd need 3
or four of these things in series to test my {36,48}V golf carts, but
that's easy enough. Anyone played with one of these things enough to
know how warm it gets, or it it ought to have a fan for cooling?

They are only good for a few seconds before they start to get too hot.
A fan would not be sufficient.

These testers are so useful and cheap that everyone ought to own one, but
they are not a capacity tester. You are really testing the internal
resistance of the battery, which I have always found to be information
enough. You can't really use them in series because they have some type of
momentary contact switch and you would quickly run out of hands trying to
click them all on at the same time.

I you really want to do a capacity test, think about an inverter and a
space heater. They cost money, but they also have other uses when they are
not testing batteries.

Vaughn

 

[Scott Willing]

Yeah, I'm beginning to think that kludging something together is the
way to go. Will a solid-state relay drop out DC voltages, or are they
(still) triac or SCR-based, and will stick on?

Of course, now my brain wants a net-metering solution, so I can dump
the power back into the grid, instead of wasting $3-5 worth of power
heating up a resistor... 8*)

FWIW, years ago a friend of mine designed an active load bank to test
honking big computer power supplies. Essentially it was a bunch of
power transistors paralleled up and suitably heat-sinked (sunk?).
Might've been a fan on the sink, I'm not sure.

The beauty of the active approach is that you can design fairly simple
control circuits to dial in the amount of current you want to draw and
to bail out at the low voltage of your choosing without an additional
active switch or relay component.

-=s

 

[[email protected]]

Step 3. Use any time left over to check for sale prices on these
items. I think I remember $9.99 making an appearance.
http://www.harborfreight.com [...]

I've really got to pay more attention to Harbor Frieght! I'd need 3
or four of these things in series to test my {36,48}V golf carts, but
that's easy enough. Anyone played with one of these things enough to
know how warm it gets, or it it ought to have a fan for cooling?

Thanks for the thoughts guys!

You REALLY should be checking each battery separately so you know if
you have one bad battery in the string. If you have one bad one in
each of 3 or 4 carts, you use one of similar capacity from one cart
for each of the bad ones, and only need to replace the full set on
one.

 

[scott]

William P. N. Smith wrote in

The golf cart industry uses a standard 75-amp current drain, so
batteries can be tested and compared using a common specification.
I'd really like to have taken measurements when the carts were new, so
I can compare to what they are now, and schedule battery replacement
for convenient times.


Our local mechanic doesn't have the discharge tester either, and
specific gravity tests show the batteries to be in fine shape when
fully charged, they just don't seem to last as long as they did when
new.

I suppose I could build something, anyone have any thoughts about 75A,
{36,48}V loads?

Thanks!

hi,
The easy (and cheapo) way to make a hi capacity load tester is to
scrounge steel strapping material used to strap heavy loads to pallets,
drill a hole in the strap ends , mount with bolts and use a continuous duty
solenoid (if you want to switch off and on) and battery cables to hook up,
experiment with lengths and maybe different thicknesses of strapping to get
the load right. I could not see any point in a timer as you will shorten
the life by running a test too long.
The hardest part about this method is building a case that won't restrict
airflow and is not conductive or flammable ( the load straps may get red
hot). I would venture a good starting point to be a cheap metal case box
fan with discharge pointed up and the load cell on top fixed to the metal
case with plumber's strap and maybe porcelain insulators from a electronic
supply house (antenna insulators maybe?). fan could help keep straps from
drooping from too much heat, buy some mechanic's safety wire (it is hi temp
stainless) to tie load strap to insulators to support it.
You wanted cheap, the most expensive part of this setup would be the
meter to measure current draw.
This is likely to evoke a lot of criticism from onlookers until you tell
them how much the alternative costs. As the saying goes, screw 'em if they
cant take a joke.
Good Luck
Scott

 

[William P. N. Smith]

You REALLY should be checking each battery separately

Hmm, Anthony mentioned this as well, but I thought that a bank was an
integral, non-separable item, and that replacing a single battery in
an old bank was a recipie for disaster.

Part of my problem is that there are at least 3 different golf cart
battery types in my 'fleet', T105s (6V, 220AH), T-145s(6V, higher
capacity), and (forget the number) 8V,165AH batteries, so swapping
them around wouldn't work well in most cases.

Also, when I test cells with the bank discharged, I don't see a lot of
difference in SG between them, so I suspect that they are just worn
out...

 

[Ignoramus15786]

FWIW, years ago a friend of mine designed an active load bank to test
honking big computer power supplies. Essentially it was a bunch of
power transistors paralleled up and suitably heat-sinked (sunk?).
Might've been a fan on the sink, I'm not sure.

That's interesting. I own a nice 100 amp low voltage load bank,
military surplus. I use it to test various power supplies that I sell,
such as HP 6260B.

i

 

[Bruce in Alaska]

Hmm, Anthony mentioned this as well, but I thought that a bank was an
integral, non-separable item, and that replacing a single battery in
an old bank was a recipie for disaster.

Part of my problem is that there are at least 3 different golf cart
battery types in my 'fleet', T105s (6V, 220AH), T-145s(6V, higher
capacity), and (forget the number) 8V,165AH batteries, so swapping
them around wouldn't work well in most cases.

Also, when I test cells with the bank discharged, I don't see a lot of
difference in SG between them, so I suspect that they are just worn
out...

Most of the commercial users now have switched to Dynamic Impedance
testing of batteries rather than Specific Gravity testing. It gives the
operator a much better picture of the state of the battery, especially
if you can get to the individual cell links and test cells individually.


Bruce in alaska

 

[Bob Adkins]

The golf cart industry uses a standard 75-amp current drain, so
batteries can be tested and compared using a common specification.
I'd really like to have taken measurements when the carts were new, so
I can compare to what they are now, and schedule battery replacement
for convenient times.

Are you saying to use golf cart batteries on a *golf cart*? <Shudder> What a
waste of good batteries!


-- Bob

 

[Bob Adkins]

I'm looking for a battery discharger for testing my golf cart
batteries for capacity. Golf cart and charger companies make them for
on the order of $500, but it's just a (resistive?) load, a low voltage
disconnect, and a clock to give runtime, so I can't imagine that there
isn't a far less expensive one available that I just don't know about.

Anyone have any sources for this kind of thing for less than the cost
of a new set of batteries? 8*|

Do you mean to do an Ah capacity test on them? Like you do on NiCAD or NiMH
cells?

I would never discharge my batteries just to test them. I'm afraid they
wouldn't survive the test!

Just do a load test. It's not as good as a true Ah capacity test, but it's a
pretty good indicator.

Harbor Freight has a load tester I have been eyeing for around $50. It has a
real carbon pile load, just like the old days.

-- Bob

 

[Bob Adkins]

I'm looking for a battery discharger for testing my golf cart
batteries for capacity. Golf cart and charger companies make them for
on the order of $500, but it's just a (resistive?) load, a low voltage
disconnect, and a clock to give runtime, so I can't imagine that there
isn't a far less expensive one available that I just don't know about.

Anyone have any sources for this kind of thing for less than the cost
of a new set of batteries? 8*|

Bah, I almost forgot!

Plug a Kil-a-Watt into your inverter and a 250w light bulb in to it.

Don't have an inverter? Wal-Mart has them for $20, big enough for a test.

-- Bob

 

[Ecnerwal]

Also, when I test cells with the bank discharged, I don't see a lot of
difference in SG between them, so I suspect that they are just worn
out...

At the risk of cries of voodoo, and I haven't built one yet and am too
cheap to buy one (yet), you _might_ want to think "desulphator". Have
not seen mention of them recently, but Home Power had a build your own
article which was available on the web last I knew. Getting some EDTA
was the other method of choice from what I recall. Claims of reviving
(not to 100%, but better than they were, in some cases much better than
they were) severely hosed batteries.

Anyone care to report firsthand on how well it did or did not do for
your batteries?

And on the subject of very minor firsthand reports, I'd like to report
success in opening up a couple of boom-box type CD players that wanted 8
batteries, which will soon be sprouting a wire I can connect to a 12V
battery instead. Not a big deal, but given that the generator makes too
much noise to listen to music, and the battery eating habits cost too
much to bother with, (and the battery bank and inverter are still a few
months away) it will improve my worksite this summer...

 

[William P. N. Smith]

Most of the commercial users now have switched to Dynamic Impedance
testing of batteries rather than Specific Gravity testing.

How does that work, and what exactly are they testing for? Does the
tester cost less than $600? 8*}

[FWIW, the cart that had been having the worst problem went in for
service this afternoon for an unrelated(*) problem and the mechanic
discovered a 48->12V converter drawing current continuously, which
probably explains the awful battery life of that particular cart. Now
that we've disconnected it (who needs headlights?) I'll see if things
improve.]

(*) Or was it? Loose nuts and high-resistance connections in the
forward/reverse switch can't have been helping much...