ECN Forum Forums General Topics of the Trade General Discussion Area Remote Amp Meter

I need to install two meters , volts and amps on the outside of a Genset enclosure so that the security guards can, on their rounds, monitor the condition of the batteries and the chargers' status. I know putting another volt meter in parallel with the existing charger meter won’t be a problem, but if I make parallel connections to the existing amp meter will that change the amp reading of both meters? I must be getting old… I used to be able to remember the simple stuff.

Put the new ammeter in SERIES with the existing one...

I gues that's the question, since the original ammeter is already in series in the circuit, desn't putting another ammeter in parallel put it in series in the circuit or will the current divide between the two meters? Will putting the ammeter in series with the first meter change the reading?

Putting a second ammeter in parallel will result in incorrect readings on both meters. Assuming the 2 meters are identical, each would read half the actual current.

The resistance of an ammeter is generally very low, so placing it in series with a circuit should not cahnge the circuit current by any meaningful amount.

Ah... that's what I was trying to remember! I'll take some readings before and after to double check. Many thanks for the kickstart.

I would just caution that you make sure that you are dealing with an actual ammeter and not a mV meter reading across a shunt, with the meter face calibrated in amps. If it is a direct reading ammeter, a second one in series will likely reduce your charging voltage slightly. Make sure you have the right VPC at the battery terminals before you button things up.
Joe

VPC? Volts per cell?

Thanks for the clarification Larry. That is exactly what I meant. Since battery cell voltage is one thing that we try to keep within a few hundredths of a volt of an optimum, it is one case where inserting an ammeter could have an undesirable effect. If the voltage control sensing is downstream of the ammeter, you probably wouldn't see a difference. Also, without knowing the circuit, I would be alert for my new wiring acting like radio antennas, sending noise back into my control circuit. I'm not saying that any of these will be a problem for you, just that they could be.
Joe

The meter I'm using is from a charger that was removed from the genset after that charger had failed. The meter face is marked DC AMPS (no Mfg name or or part number) and the schematic shows it in the charging current path. The system is 24 volts, Six cells/jar, 2 jars. What should my equalize and float voltages be? I was estimating 28v volts equalize, and 26v float. Oh for the record, the new charger is a Charles Industrial Group C-Charger, Mod # 93-AA2410. The manual has no schematic and no TP voltages. It just has a chart with the idiot light positions. The previous charger had Test Points I could tie to to verify the charger meters'accuracy and the remote meters.

You didn't specify the battery chemistry but the voltages sound a little low to me. Aim for the middle of the range on your battery data sheet since the cells will vary. I found an "AA2410" ferroresonant but not the 93...
Joe