Motor power/voltage monitoring question

[Iflyasa]

Originally Posted by rottie

IF you have an isolated reducer and do not have the output connected to either lead of the battery, then it will work in either lead of the system, otherwise is must go in the negative lead. (electronic design limitation) i.e. between the negative battery terminal and B- on the motor controller.

Just follow their schematic/instructions for the model you purchased for wiring these combo volt/amp/watt/Ah meters.

Did you buy the 1000amp version?

If you do not connect an isolated reducer to the meter but just the battery leads, then it must be in the negative lead, with a limit of 90VDC (on my unit).


I am sure this has been said before, but the battery system should never be connected to the chassis, it must float/electrically isolated.
To check is a simple matter of using a DMM between either battery terminal and the chassis. It should always go to ~0.0VDC (it may take a couple of seconds). This is a safety and possible corrosion issue/electrolysis. As you get higher and higher battery voltages, (think 300VDC) it becomes a real concern with non isolated batteries.

Ok let me make sure I'm am correct here. Yes I got the 1000 amp system. I will hook the meter to the negative battery at -48V going to the -B in the controller..

Now, to power the actual meter, should I use one of my 12V voltage reducers? It's on a master switch so I can control the power to it? Nothing is grounded to the frame.

Great info!

[Volt_Ampere]

Does anyone make an isolated reducer? If not, you can get an isolated 12V to 12V Supply to power the meter. I am looking at one from Digikey that is $11.21 (250mA)
Part number from them is 445-3279-ND for the surface mount version. They make a through hole version as well. I plan to use one of these to isolate my 12V reducer from my electronics. My reducer is switched by the key switch which is what I want. I have another reducer but it's not switched or isolated so I can't use it.

[Iflyasa]

Originally Posted by Volt_Ampere

Does anyone make an isolated reducer? If not, you can get an isolated 12V to 12V Supply to power the meter. I am looking at one from Digikey that is $11.21 (250mA)
Part number from them is 445-3279-ND for the surface mount version. They make a through hole version as well. I plan to use one of these to isolate my 12V reducer from my electronics. My reducer is switched by the key switch which is what I want. I have another reducer but it's not switched or isolated so I can't use it.

What exactly do you mean by "isolated"? Regarding my reducers. I have them installed with the 48V input from the 1 and 6 batteries, then it spits out 12. I have a master switch that I use to make a contact so the 48 enters the reducers. So master on, all 3 power up at 12v. Power off, 2 of the 3 are unpowered, where as my 3rd reducer has a Low power 12v for battery memory.

Do you know if this needs a constant 12v for memory, or can it simply be on and off?

The way I'm thinking is 12v off one reducer controlled by the master reducer switch. Does that sound right?

[Sergio]

This is another option from Mouser that You can switch ON/OFF at the key switch power instead of daisy chain it out of the existing 12v converter:

http://www.mouser.com/Search/Product...HOJLyanA%3d%3d

Iflyasa, isolated in this context means the +12v output can not have any reference to the negative on the input side.

The vast majority of DC-DC converters share a common negative for input and output which means if you use one of those converters You cannot measure any voltages higher than the meter power supply (30v in the case of the meter you showed).

If You want to verify what kind of DC converter You have, just measure the voltage from the +12v output to pack negative.

If You get any voltage reading, the converter has a "common" negative and it cannot be used.

[rottie]

Thanks "Sergio", That is a better explanation of "isolated" than I gave, i.e. isolated in this context means the output can not have any reference to input.

Unfortunately being an electrical engineer, I sometimes forget the terminology does not translated well.


"Iflyasa", does this help?
I have found when looking for an isolated reducer (DC/DC converter) to purchase, if they say "isolated output", then you have a chance of an isolated converter.

I also test with a DMM from each output pin of the reducer (while powered from main battery) to the + and - battery terminals. It should always go to 0.0VDC within a couple of seconds. If you get any voltage, then it is NOT isolated!!!

Again never ASSUME and we all know what happens when that is done.

[Volt_Ampere]

Isolated means not common ground. Most reducers have the 48V negative and the 12V negative connected inside. That is not good for instrumentation with a shunt. (and it won't work with many of the meters out there that require an "Isolated" supply.

[Volt_Ampere]

Hi Sergio. I looked at that converter and yes you can run it off of 48V but then you have to separately switch it. Since my converter is already switched, it is easier for me to use a 12V to 12V isolator connected to my converter output. Since I am only using 100mA or so, it really doesn't matter much to me which way I go but I want it switched so that it doesn't draw current when my cart key switch is off.

[Sergio]

Originally Posted by Volt_Ampere

Hi Sergio. I looked at that converter and yes you can run it off of 48V but then you have to separately switch it. Since my converter is already switched, it is easier for me to use a 12V to 12V isolator connected to my converter output. Since I am only using 100mA or so, it really doesn't matter much to me which way I go but I want it switched so that it doesn't draw current when my cart key switch is off.

Isn't this just a matter of connecting that reducer to the switched "Input" side of your converter (or cold side of key Switch) ratter than the +12v output side of your converter?

I agree either type works.

[Iflyasa]

I bought 2 meters. Both are not identical. The first one uses wireless to transmit the "data" to the monitor. I have 3 reducers. I plan on hooking this one on the common negative off all three. I just want to monitor all 3 collectively.

The 2nd meter, is like the 500amp version posted earlier but with 1000amps.

Yes my reducers take 48v in , and the ground is the common at the #6 battery at -48. So I am assuming none of my reducers are isolated.

Do I need to isolate the meter monitoring all 3 reducers as well? Obviously 12V.
The other meter will be monitoring my total amps between +48 and -48.

My total monitoring meter for the carts motor and accessories



And here's my wireles version to monitor my reducer usage only.



Soooo talk to me goose. Apparently I have to isolate the 1000a for my motor. So what do I need and how?

Do I need to isolate my wireless version to monitor the reducers?

I was going to power +12 from one of my reducers to power both, or do I need to use it differently?

Thanks guys

[Sergio]

Just some background Information:

The amp meters are really just precision milli-volt readers. They depend on the external shunt reaching 50mv, 75mv or 100mv (depending on the meter) at the maximum rated current.

Most of those Chinese shunts are a combination of 100Amps shunts in parallel and are calibrated by using a "hacksaw" (You can actually see where they cut all of the shunts to calibrate the output).

The isolated requirement has nothing to do with current reading, but voltage reading and how much electrical isolation is built in the meter electronics.

If you notice on the first specification that You posted, the maximum voltage reading when using the internal power supply is the limit of the meter power supply voltage (40v).

Internal Power Supply in this context means it shares the same reference power as the circuit being measured.

There is no limit on the current reading regardless how the meter is powered.

If that meter is connected to where it would only read a 12v battery, no isolation power is needed.

I cannot open the PDF manual for the second meter (we block China traffic at work), but it looks like it uses a NRF24L01 wireless transmitter attached to the shunt, so that will need its own separate power.

You really need to look at the specifications for each meter as there is no standard requirement.