24vdc charger problem

[rall]

Just trying to figure out why my 24vdc charger has a 35 vdc charging output, this unit is 120 ac stepped down to 24vac then to 24vdc rated at 400ma but im reading 35 vdc off output, any ideas?? This is a charger for an electric scooter. any help would be appreciated.

 

[smanches]

You need to load it down at it's rated amperage before reading the voltage. Since there is no load, the output can be much higher than it's rating. It's normal for transformer based chargers.

 

[#1supertech]

rall,

"smanches" is right in his post reply.

As an example -

With a standard 6-volt charger (open circuit NO LOAD applied btw) on average you'll read about 2.6 volts higher then the rated DC Output.

So for a 24-volt charger you should see around ~34.4 volts "minimum", but nothing much higher - again - depending on the quality & CAL of your DVM as well - as far as its accuracy goes.

With the charger under a LOAD (batts are in charge mode now) you should now see a regulated voltage of ~29.4 volts DC at full batt charge and the charger going into top off mode - depending on the quality and features of the charger itself. If it's a cheapy charger (which I suspect it is) then you probably only have 2 LED's, and one is usually for Power ON, while the other one is the CHARGE indicator - switching OFF & ON when the batt charge capacity is FULL. Just depends on the Mfr brand.

If the batts under charge have been severely drained then initially the charger will read something like 25 volts to start with as it slowly ramps up to the cutoff point of roughly 29.4 volts. That's taking into account that both batts are indeed GOOD to start with.

One thing that bothers me is that you are saying the DC output charge current is only 400ma. Are you sure?

What is the Ah rating of each batt? I'm guessing that it's 12ah unless you have a much bigger scooter there. If they are 12ah batts it will take a pretty long time to charge them back up at 400ma. Must be a pretty conservative charger as most scooter chargers that I repair are all 2A rated.

If your scooter's PWM controller has a fixed cutoff point of anything less then say 22 volts on it (like most do for a 24-volt system) then you are looking at least at a 10-12 hour charge cycle time to fully top off the batts.

On your scooter there does it have a LED batt capacity meter by chance? Usually it's 4 colored LED's mounted somewhere on or near the handle bar assy.

Btw - does your charger there actually say its DC Output is 24-volts DC? Or is it an AC to AC step-down adapter with the actual DC charger section onboard the scooter itself. Reason I ask is because you stated the 120VAC was stepped down to 24VAC and then to 24VDC. Where are you seeing or measuring that? Have you also opened up the charger by chance? Just curious here is all?

Let me know if it’s charging properly - other then that I guess all is well.

Best regards,

Frank

 

[rall]

Hi, thanks for the help guys, anyways, the transformer's ratings are 24 vdc 400ma, i had to replace the step down, i replaced it with a 24 vac 20va, i just wanted to know if the 35 vdc was normal, it does make sense with no load it would be higher but with some power supplies i use in my line of work the charging voltage are much closer than this one.

 

[smanches]

Switched power supplies (which are almost everywhere now and replacing transformer based supplies) will show a much more normal voltage unloaded because they have regulation circuitry built in.