Emulating 24v Deep cycle lead acid batteries to check chargers after repair

[Labrat101]

  Hi . I have been given a load of damaged mobility charges for repair . 24v & 36v  @ 6 or 8 amp
 These chargers have a relay on the output so if its 24v charger it has to have at least 20v for the sense circuit to start the charge cycle
At the moment I have 3 accumulators stuck under my bench  ie  2 in series for 24v  .  Being deep cycle there full charge voltage is 14.8v .
I have been trying to Emulate a lead acid Deep cycle battery with a 10 amp 0-60v lab power supply with an Array electronic load.
 Then lets say . A 24volt charger when it sees 20v from the PSU  it should operate the sense relay which it does . and then start charge cycle  which
is 29.5 v @ 2 - 8 amps ramps up or down .
I fitted a large IOR 100Amp diode (0.2 voltage drop) on the power supply to safe guard my power supply . The array electronic load is directly on the charger .
I tried setting it to 5 to 8 ohms . This works only for a few seconds before the controller chip sees it as an error.
If connecting to a real batteries the chargers work fine .
But this is a very slow process as most of them need calibrating , Charging the batteries to well over 32v .  Each battery should be 14.8v / 15v Max .

 I was wondering If any one has managed to Emulate this type of battery /s   
I know there are ready made units but are very pricey and I don't repair enough of these chargers to make it worth my while .
So if there are some good ideas I would love to hear .

 Thanks

[Hydron]

Why don't you set the load to a constant voltage, to better look like a real battery which is basically a voltage source. If you set it >20V it won't affect the PSU you're using to kick the process off, but will start to sink current once the charger starts.
Crank up the voltage during the "charge" to simulate the battery filling up. You'll need a load which can handle the power dissipation, but 32V * 8A is under 300W, which many inexpensive loads will handle fine.

Or if the load isn't beefy enough, add it in series (still in voltage mode) with a resistor sized to drop say 25V @ 8A, so most of the power goes into the resistor. Would be more annoying to adjust (would need a separate meter too).
Go get some buckets of water and magnet wire if you want to make a cheap high power dummy load, thanks mikeselectricstuff for this trick!:

[calzap]

I’ve found that rather than try to emulate a battery attached to the charger terminals “as is” that it’s easier to disconnect the voltage sense wires from the charger output terminals and use a small power supply to apply different voltages to the sense wires.   This allows easy testing of voltages to start cycle and end cycle.   Some chargers may use a timer.  I’ve used a simple bank of power resistors as the load because initially, I didn’t have variable DC load with sufficient capacity.  I have a bigger electronic load now but haven’t felt the need to use it for this application.  So far, has worked OK for the types of chargers I deal with.   However, may not work for some newer types that use pulse charging, and for some chargers, it may be difficult to access the sense wires.

Link below shows the setup with power resistors.

https://www.eevblog.com/forum/projects/simple-load-for-testing-lead-acid-battery-chargers/msg2878664/#msg2878664


Mike in California

[Labrat101]

 unfortunately These mobility chargers don't have direct access to the sense wires .  I can read the voltages before and on the sense connections just behind the relay. The controller panel is mounted vertical . Horrible design for service . to replace parts in the output stage the relay has to be removed .
 My Old Array 3710A is the old version which goes to 200w @ 30A but it only has  Watts , Resistance  & Amps .
I do have a bigger 500w load which I made the control is a bit ruff and jumps up to 30A to fast.  waiting for parts to fix.
 
 These chargers are made only to charge Deep cycle acid or gel batteries . Regular car type accumulators the sense circuit ignores them and wont charge.
 one of the charges has program chip on the board with one time programing as far as I can figure . That one works and I going to return that back to the user
as is . The one that is causing a problem is over charging by 2.5 volts and not sensing until the battery is below 20v which is too low .
and to make life easy the controller board the chip numbers have been erased .

 The resistor in a bucket is not a bad idea . Other than large amount of water and electric maybe more fun 
I really prefer working on standard chargers they are so much easier .

I may have to put some jumpers on the sense circuit as suggested that maybe a good work round . Thanks