ECN Forum
Posted By: jkochan Remote Amp Meter - 06/08/07 09:06 PM
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.
Posted By: NJwirenut Re: Remote Amp Meter - 06/08/07 10:12 PM
Put the new ammeter in SERIES with the existing one...
Posted By: jkochan Re: Remote Amp Meter - 06/08/07 10:23 PM
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?
Posted By: NJwirenut Re: Remote Amp Meter - 06/08/07 10:46 PM
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.
Posted By: jkochan Re: Remote Amp Meter - 06/09/07 01:28 AM
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.
Posted By: JoeTestingEngr Re: Remote Amp Meter - 06/09/07 01:51 AM
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
Posted By: LarryC Re: Remote Amp Meter - 06/09/07 02:40 AM
Originally Posted by JoeTestingEngr
Make sure you have the right VPC at the battery terminals before you button things up.


VPC? Volts per cell?
Posted By: JoeTestingEngr Re: Remote Amp Meter - 06/09/07 01:46 PM
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
Posted By: jkochan Re: Remote Amp Meter - 06/11/07 03:37 PM
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.
Posted By: JoeTestingEngr Re: Remote Amp Meter - 06/12/07 03:14 AM
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
Posted By: e57 Re: Remote Amp Meter - 06/12/07 03:28 PM
Originally Posted by jkochan
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.


The 'security guards' are monitoring this??? If the location has a CCTV system, install a camera veiwing the control panel. Or is the idea to have them actually walk around and have something to do?
Posted By: jkochan Re: Remote Amp Meter - 06/12/07 07:30 PM
The security guards make their rounds and the generator / cooling tower yard is on the route. This happens all day long along with my routine inspections. In critical areas, they are instructed to observe and in certain cases document the status of certain pieces of equipment. Anything out of the ordinary; readings beyond what is posted as normal for that piece of equipment, temperatures which seem out of range are brought to my attention for investigation. Most critical areas and equipment have a variety of sensors but we have always had visual, regular inspections of all building systems.This involves us training security in the operation of the building systems most critical to safety or most likely to cause major physical or fiscal damage if not detected early.
Posted By: Alan Belson Re: Remote Amp Meter - 06/12/07 08:59 PM
Quote
The 'security guards' are monitoring this???


Ah! Happy days, being woken at 3am by SGs to say "Mr OnCallEngineer, there's a red light showing in building xyz". Then driving 25 miles in the pouring rain into Wales to find a neon that had been happliy glowing for years but only just noticed! Neeearrgghhh!
Here!! I just thought, you don't suppose they saved it up for the foulest night possible just for a laugh do you?

Alan

Posted By: jkochan Re: Remote Amp Meter - 06/12/07 09:52 PM
Yeah been there..done that...but my company pays a minimum four hours OT if I get called back for any reason, and it starts the minute I'm out my door. If they call me back and say "never mind" I still get paid. That being said, I've been doing this long enough that even half asleep, I know which questions to ask, in what order and how often to make a value decision on whether or not to roll on a call. But, it's give and take. If there is ANY doubt whether I should go in.... I go in. That's my call and if I'm wrong, I don't penalize the company for it I'm not that far away and so far my company has always treated me fairly. Our BAS allow me to dial-in from home and evaluate certain systems and areas. Our security personell know they can call me at any time without getting their butts chewed out. In return they work with me on figuring out what's going on and sometimes we both learn something new.I would rather them call me about a fast drip they saw on one of the Reverse Osmossis sytems than extract 500 gallons of water out of a carpet BEFORE I can vacuum, blow and test all the floor circuits.
Posted By: gfretwell Re: Remote Amp Meter - 06/13/07 01:32 AM
I think they are using hall effect meters in newer marine charging applications. They have virtually zero insertion loss.
Posted By: jkochan Re: Remote Amp Meter - 06/13/07 08:37 PM
Unfortunately, I need to hook up the existing and not re-invent the wheel. They can see the value in having their generator start when needed, but not in non-parasitic metering.
Posted By: e57 Re: Remote Amp Meter - 06/14/07 06:46 AM
Still think you should install a camera, especially if it is important, better still Internet accessible - then everyone could watch it on the Internet from home if they like. wink
Posted By: JoeTestingEngr Re: Remote Amp Meter - 06/14/07 11:51 PM
I didn't see a manual for the model # you provided. The closest I saw was a reference to a ferroresonant unit with auto-equalize. If this is what you have, there is no one specific voltage or current that you would see. Currents would peak when first going into EQ., and drop to next to nothing when shifting back into Float. Then consider parallax errors and different individuals' readings of analog meter faces.

Does your charger provide the compliment of alarms that many of the new ones include? If so, consider driving two or three indicators on the exterior. Use one fused supply off of the battery string and make sure that at least one is always on. You could use green for all OK, red for under or over voltage, amber for minor alarms, Et.C.

I can't tell you the battery voltage of any of our substation strings. Let any one of them drop below 125 VDC or loose it's AC supply, and we'll know about it within a few seconds. If you use a long-life green cluster LED for normal, and blinking clusters for alarms, you'll get the fastest response possible without wires or transmitters..
Joe
Posted By: jkochan Re: Remote Amp Meter - 06/19/07 05:51 PM
Thanks to all. Meters are in, everything seems to be within specs.
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