Battery Charger V/Ah

 Hi!

    I tested some battery chargers last night , and found "as usual"
that the amps and voltages stated on the modules were not the same as what I
found on the Volt and Amp testers....

    Some 12v charging modules, would say 1.5 amp, whereas the voltage
test was 12-->17v and/or 4-->6amps on the meters....

    All the "Walwart" max output 800ma (.8A) with 3 volts selected
showed 2amps on the amp meter, and almost 4amps at the 12v setting. The
inline charging modules were pretty much the same...

    I have a 12v 8Ah MF SLA battery to charge at .8amp and I can't get
anything to charge as low as .8 amp from the walwarts.......when I do,
nothing happens for days, as far volt checks are concerned...

    The charging volts are not higher than 12.4 volts on any of the
chargers....

    Some ppl discard this discrepancy with the volts compensate for the
current, expression, but does it really, if a low charging amp can't be
achieved? I don't want to buckle cells or dehydrate the $240 MF SLA battery.

 


Your post doesn't make a whole lot of sense.

You need more than 12.4V to charge a 12V battery. If you want to limit the
current, use an LM317 wired as a constant current source, choose the
resistors accordingly to set 800mA.

 wrote:

|>
|>> Hi!
|>>
|>> I tested some battery chargers last night , and found "as usual"
|>> that the amps and voltages stated on the modules were not the same as what
|>> I
|>> found on the Volt and Amp testers....
|>>
|>> Some 12v charging modules, would say 1.5 amp, whereas the voltage
|>> test was 12-->17v and/or 4-->6amps on the meters....
|>>
|>> All the "Walwart" max output 800ma (.8A) with 3 volts selected
|>> showed 2amps on the amp meter, and almost 4amps at the 12v setting. The
|>> inline charging modules were pretty much the same...
|>>
|>> I have a 12v 8Ah MF SLA battery to charge at .8amp and I can't get
|>> anything to charge as low as .8 amp from the walwarts.......when I do,
|>> nothing happens for days, as far volt checks are concerned...
|>>
|>> The charging volts are not higher than 12.4 volts on any of the
|>> chargers....
|>>
|>> Some ppl discard this discrepancy with the volts compensate for the
|>> current, expression, but does it really, if a low charging amp can't be
|>> achieved? I don't want to buckle cells or dehydrate the $240 MF SLA
|>> battery.
|>
|>Your post doesn't make a whole lot of sense.
|>
|>You need more than 12.4V to charge a 12V battery. If you want to limit the
|>current, use an LM317 wired as a constant current source, choose the
|>resistors accordingly to set 800mA.
|>

 "Walwarts" = Universal Chargers

    A Universal Charger's max 800mA "Walwart" will read 16v as a
charging current, when set at it's max 12v.

    The current/amps will read 2--->3.5amps at 12v, which is something I
never really understood, since the Universal Charger is not rated to go or
handle more than .8amps maximum?

    At the highest setting, the Universal Chargers won't do much unless
your talking days to charge an older battery at it's rating 800mA......

    Are the Universal Chargers defective, most electronics shops say no,
and they are rated correctly....?

    I usually put the battery on an older UPS that had the same battery
and I get good results on that.....It (voltmeter) reads 14v at 1.2amps

    Am I confusing the .8aH suggested charging rate of 10% for an 8amp
battery with the Universal Chargers 800mA.

 Robert LaCasse wrote:


<snip>

I almost responded to your first post but then I read the thread first
and James reply was everything I would have said.

What they do with cheap chargers limit the output by the windings on the
transformer and the physical size of the hunk of soft iron in it. There
typically isn't any regulation, just retification. If you really want to
see something that will tie your shorts in a knot, just charge up a high
value capacitor with the output. You may see >25V DC at no load! There
is some buzz word they use, something like 'magnetics regulated' which
just means the current drain will lower the chargers output voltage.
That is, it will put out say 16V into a 1 amp load and 11V into a 2 amp
load. I think your observation is ~'This is a wacky way to do things' is
right.

Really, go with a 317 set up as a constant current source if you want it
done right but don't want to go the $120 charger route. In a perfect
world you should set up a charger with two 317s: First one to regulate
the DC voltage to ~16V max<to allow for forward voltage drop on the 2nd
317 and still have over 14.7V you want for charging> and the second one
to limit current to the .8 amps you are looking for. It would only cost
you a couple of bucks to do it that way.

Just a couple of BTWs, I had one of those cheap 'float' chargers and it
smoked. Just no way it limited anything but its own life. I will never
buy another. My 55 amp charger will boil/melt a motorcycle battery even
when set on its lowest setting.

Rick

 wrote:

|>Really, go with a 317 set up as a constant current source if you want it
|>done right but don't want to go the $120 charger route. In a perfect
|>world you should set up a charger with two 317s: First one to regulate
|>the DC voltage to ~16V max<to allow for forward voltage drop on the 2nd
|>317 and still have over 14.7V you want for charging> and the second one
|>to limit current to the .8 amps you are looking for. It would only cost
|>you a couple of bucks to do it that way.

    For some reason, the Yamaha Shop Manual's instruction from GP is
that (a constant current charger is not suitable for charging MF batteries)
and conventional chargers may harm the MF battery as well....

    Your explanation on the Voltage/Amperage was quite suitable as I
have noticed and heard over and over again......so it must be true heh.....