Golf Cart Battery Charger Testing

[electricMN]

I'm repairing golf cart battery chargers for a local shop and I need a way to test them before I say they're working. I currently can only test the 36V battery chargers because I have a golf cart that uses six, six volt batteries. I'd like to be able to test the chargers on the bench since the battery chargers can be for 24v, 36v or 48v. I have no way of testing the 24 & 48V chargers.
Some of the battery chargers need to see a certain amount of voltage before they will even turn on to begin charging. For example, certain 36V chargers need to see at least 27V before they will charge the batteries. Would an electronic DC load work in this situation? I'd need to be able to adjust the voltage and the current in order to simulate a battery charging in order to make the charger go through the complete charging cycle.

Any thoughts on what would be the best way to achieve this to allow bench testing?

TIA

[fordem]

I would suggest a bank of batteries that could be reconfigured - say four 12V automotive batteries.

[electricMN]

I was trying to avoid that since it would take up a lot of room and I don't like the thought of the vapors from the batteries in my house.

But thanks for the suggestion.

[pqass]

Maybe you can get away with a few small gel cell batteries+diode in parallel with the DC load and the battery charger under test.  See attached.

The DC load (initially set to some minimum) will draw from the gel cells (left side of diagram).  When the battery charger (DUT) is switched on it will see a voltage which, hopefully, will cause it to engage its charging cycle.  The charger will output a higher voltage so the gel cells will be protected by the diode (won't actually be charged) and you will have full control over the current sunk by the DC load.

Pro: won't require full set of high capacity batteries; just small-ish gel cells.
Con: the battery charger (DUT) may kick in/out of its charging cycle so the gel cells should at least be able to briefly sustain the current level set by the DC load.

On second thought, instead of using gel cells, you could use a variable power supply (diode VERY important to prevent its destruction) since the charger will be looking for progress; ie. the "battery" (dummy voltage source) should be rising in voltage and current sunk tapers off as the charge cycle progresses.


Attachment source here: http://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgoqoQFMBaMMAKADdwAWTkT4wrjxQIBVKpyq4o0mAhYATQSGEDs2ASuUh5dAGYBDAK4AbAC4sA7hW69+IQhhS3RLAE7PeYAX292x0Vg4HJx97R2URGV5xMRloOWwMKkJ8CN8NSIgxFkTJdTSPTSyoFgBne1TNYILYg2NSuksPUIQbUMgWfWVw7AQndTwQXqdicCQmJDB4eCgA0mJOAkhsPDBiBGwpp1RkabchwkHh3mx+vukpjt0Ts5C7Y9PeXgDCV7f3t4wmzH7D7pCvCUrD9POlQUDmoDQgMSrlCpFoflih0AEr-Ib5FAoHhqUTSCSzbZxOQABxAOAyAgpHmRTWpoWq7TpmMi1U0HTJhCErJ4oVpVi5NLafiagqKNnZLDJrV5gJlNJkTTAwrBTOlNlx1llAn5WvBoU4gI6VnlmsRLgAHhQFuAyCA8JAIFjyEIeAAdUoer2en0egAiAFUACput0AOwAFAAhfSmUx0VwATw9AGEABb6VwAcwTAEoWFapGgnZxyChNk9sSBvX7DABbOvJ0psAD2Zn0OdDYdKLcMrgAxnQPaYWx7dC22-7gwXlH8+hAEMQFwgIK7q76fX6Ux6ADIt-TyLsRhpD0oASQapgAVFMPaVjABLHSuD0tsMe1wPrNp0z5lbgAQADFkXAEAmBAC86FMD0rw9KYWCAA

[electricMN]

"the charger will be looking for progress; ie. the "battery" (dummy voltage source) should be rising in voltage and current sunk tapers off as the charge cycle progresses."

Yes, this is what I need. I will study your diagram and see if it makes sense to me. I thought about using a power supply to simulate the battery voltage but I'm not sure how to do that so the battery charger and the power supply don't fight each other.

Thanks!

[Jeff eelcr]

They make large gel cell batteries for automotive they are sealed so
no leaks no gases no mess more money.
Jeff

[pqass]

"the charger will be looking for progress; ie. the "battery" (dummy voltage source) should be rising in voltage and current sunk tapers off as the charge cycle progresses."

Yes, this is what I need. I will study your diagram and see if it makes sense to me. I thought about using a power supply to simulate the battery voltage but I'm not sure how to do that so the battery charger and the power supply don't fight each other.

Thanks!

The power supply will need to be capable of outputting as much current as your highest DC load test current (same as your DUT?), otherwise, the PS voltage will collapse (constant/over current protection kicks in or fuse blows or self destructs).  And if the PS voltage drops to zero, the DUT (battery charger) will stop.  Therefore, a switching supply capable of 52V @ say, 20A should suffice?

A fully charged lead acid battery bank (6, 8V cells) is 8.43V*6 = 50.6V.
If the bank is depleted then its voltage is 7.72V*6 = 46.3V.
https://batteryuniversity.com/article/bu-903-how-to-measure-state-of-charge

So, start with the DUT (charger) off, your PS on and set to 47.3V (we add a volt for the diode drop), and your DC load on and set to 20A.  Then, turn on your DUT.  Since the DUT now provides the higher voltage causing the diode to be reverse biased, the 20A consumed by the DC load now comes solely from the DUT. Slowly raise the PS voltage and lower the DC load current.  PS voltage must not exceed 51.6V (full bank+a diode drop).  I'm not sure how long "slowly" should be.

[electricMN]

Thanks for the information. I'll get the required stuff and give it a try. I may have more questions along the way.

So I need to get a power supply and a constant current electronic DC load, correct?

[pqass]

Thanks for the information. I'll get the required stuff and give it a try. I may have more questions along the way.

So I need to get a power supply and a constant current electronic DC load, correct?

Yes.  And a diode.  The diode is VERY important! 

The diode has to be able to take your max. DC load current (not for long; just until the DUT kicks in; 20A in my example) and have a peak inverse voltage greater than your battery charger max. voltage (50-60V in my example).  Try to find one with a foward voltage drop of less than a volt if you can.