Layman's question: Digital display of power supply supposed to show actual or target voltage?

[fancy nospam tunes]

Thinking of buying a variable DC power supply to recharge an electric
scooter's sealed gel lead acid battery. However, when trying out two
models from the same manufacturer, their voltage displays aren't
consistent:

The less powerful model (0-3amps) shows actual voltage, as it rises
from actual voltage, until it stops at the target voltage [using
Constant Voltage mode.] Whereas the more powerful model (0-10 amps)
shows only the target voltage; requiring the user to use a multimeter
to view the actual, rising, voltages. I personally prefer to see the
actual voltage.

Can someone explain why these power supplies' displays differ?

Second newbie question: Is the more 0-10 amp unit a more
"professional" design? I'd like to have a power supply that doesn't
self-destruct as soon as the warranty expires.

All perspectives totally appreciated. Cheers!

 

[James Meyer]

Thinking of buying a variable DC power supply to recharge an electric
scooter's sealed gel lead acid battery. However, when trying out two
models from the same manufacturer, their voltage displays aren't
consistent:

The less powerful model (0-3amps) shows actual voltage, as it rises
from actual voltage, until it stops at the target voltage [using
Constant Voltage mode.] Whereas the more powerful model (0-10 amps)
shows only the target voltage; requiring the user to use a multimeter
to view the actual, rising, voltages. I personally prefer to see the
actual voltage.

Can someone explain why these power supplies' displays differ?

Second newbie question: Is the more 0-10 amp unit a more
"professional" design? I'd like to have a power supply that doesn't
self-destruct as soon as the warranty expires.

All perspectives totally appreciated. Cheers!

You are completely missing the second vital measurement, current.

The lower powered supply is probably supplying a constant current of 3
amps when it is connected to the battery as long as its voltage control is set
to something over the voltage that the battery is showing before it's connected.
So the voltage supply is showing the battery's terminal voltage as it charges.

The higher powered supply is apparently producing enough current to
raise the battery's terminal voltage instantaneously to the value you set with
its voltage control.

The proper supply to use for battery charging is one with separate
current AND voltage setting knobs. That way you can set the charging current
AND the voltage at which the supply will stop delivering charging current.

Jim

 

[Mac]

Thinking of buying a variable DC power supply to recharge an electric
scooter's sealed gel lead acid battery. However, when trying out two
models from the same manufacturer, their voltage displays aren't
consistent:

This is a terrible way to recharge a "gel cell" battery. Buy a charger
designed for gel cell batteries or one that has a setting for them.

There are recommendations about current output as a function of battery
capacity, but I don't know what the exact rule of thumb is.

The way these chargers work (more or less) is that they charge at max
current until the voltage reaches some threshold (maybe 14 or 14.5 ?),
then they charge at a constant voltage for some period of time (several
hours?), and after that they go down to a smaller float voltage (~13 or
13.5 ? ). I like gel cells, but they are (according to what I have
read) somewhat less forgiving of high-voltage charging than liquid
electrolyte batteries. There is some kind of a battery newsgroup,
sci.chem.electrochem.battery, I think, and they might have additional
insight over there. Read the faq before posting, of course.

The less powerful model (0-3amps) shows actual voltage, as it rises
from actual voltage, until it stops at the target voltage [using
Constant Voltage mode.] Whereas the more powerful model (0-10 amps)
shows only the target voltage; requiring the user to use a multimeter
to view the actual, rising, voltages. I personally prefer to see the
actual voltage.

Can someone explain why these power supplies' displays differ?

Second newbie question: Is the more 0-10 amp unit a more
"professional" design? I'd like to have a power supply that doesn't
self-destruct as soon as the warranty expires.

All perspectives totally appreciated. Cheers!

I don't think anyone can tell you which is a more professional design
based on the few facts you have provided. However, I would definitely get
a dedicated charger, not a variable DC power supply.

For example, a quick search led me to the Xantrex Xpower 15. I'm not sure
this is a good charger, but it says that it supports sealed gel
electrolyte lead acid batteries, and it has three stage charging, (which
is what I described above). It is for batteries in the 6 to 200 Ah range.
Your battery probably falls in there somewhere. At least I doubt it is
more than 200 Ah.
;-)

Best of luck, whatever you decide to do.

--Mac

 

[Rich Grise]

This is a terrible way to recharge a "gel cell" battery. Buy a charger
designed for gel cell batteries or one that has a setting for them.

There are recommendations about current output as a function of battery
capacity, but I don't know what the exact rule of thumb is.

You charge them with the standard lead-acid charging curve, but you have
to take care to keep the volts/amps below some threshold where it starts
gassing, since they have no vents.

Cheers!
Rich

 

[Active8]

You charge them with the standard lead-acid charging curve, but you have
to take care to keep the volts/amps below some threshold where it starts
gassing, since they have no vents.

Good point about the gassing. It sounds like the OP tried it out,
too. I'm glad he didn't get hurt.

Maybe I'm a bit paranoid, but I'm glad my UPS has a metal case.
Those auto quick starters seem to have a sturdy enough case. But
what about those cell phone batts blowing up under charge. Scary.

If the "scooter" came with a recharger, a mfg replacement is the way
to go.

Safety First.

 

[Fred Bloggs]

Thinking of buying a variable DC power supply to recharge an electric
scooter's sealed gel lead acid battery. However, when trying out two
models from the same manufacturer, their voltage displays aren't
consistent:

The less powerful model (0-3amps) shows actual voltage, as it rises
from actual voltage, until it stops at the target voltage [using
Constant Voltage mode.] Whereas the more powerful model (0-10 amps)
shows only the target voltage; requiring the user to use a multimeter
to view the actual, rising, voltages. I personally prefer to see the
actual voltage.

Can someone explain why these power supplies' displays differ?

Second newbie question: Is the more 0-10 amp unit a more
"professional" design? I'd like to have a power supply that doesn't
self-destruct as soon as the warranty expires.

All perspectives totally appreciated. Cheers!

Both supplies will attempt to maintain the constant set voltage at their
output terminals up to the maximum current limit, at which point they
will abandon voltage regulation and maintain a constant maximum current
drive into the load. Obviously the 3 Amp unit hit this threshold at a
voltage lower than setting, the 10 Amp did not hit its maximum current
threshold and was able to supply the full voltage.
This is not the best way to charge gel cells, it is a taper charge
method, where despite the capacity of the power supply, charge current
does taper to zero strongly as battery cell voltage reaches full charge.
You will get something like 70% the number of charge cycles to battery
failure this way as compared to a three-stage lead acid battery charger.
It's your call.

There's no reason for the power supply to fail if you exercise it
thoroughly during the warranty period to accumulate hours. The most
common failure mode is end user abuse.