Voltmeter Acting up. need help!

[mrcshbs]

Hi,

My name is Marcos and I working on my first EV, the car is pretty much done, but there is only on problem.

I have added a 200V DC digital meter to the dash to monitor my 72V battery bank… the meter works fine when the car is first turned on, but as I press the accelerator and a load is applied to the big DC motor the goes displays some crazy numbers.. when I take my foot off the accelerator, the meter goes back to normal.

The meter has 4 wires in the back, 2 of them are a 12V isolated power supply.. and the other 2 are for the readings.

They are connected directly, I mean, the wires go from the meter to the battery bank and the 12V battery (power supply)

Is there any way I can correct that??

I have a cheap multi-meter I got from RadioShack, when I connect it, reads fine.. but this cheap meter also shows the meter when I accelerate the car as well…

Is there maybe a diode or some other device that I need to connect to this meter to make it work?

Please let me know

This is the meter I am trying to use (not the RadioShack multi-meter one)

Thank you.

 

[crutschow]

Sounds like electrical noise from the motor is getting into the meter. You could try a filter at the meter input, say 1k ohm in series with the battery lead to the meter and 1µf or more across the meter input.

The Radioshack meter may have a filter built in to the input.

There's another possibility. Is the 12V actually isolated from the 72V battery or is there a common ground through the controller? You diagram doesn't show a common but there very well may be one. Many meters need a truly isolated (floating) supply for proper operation (especially since you mention an isolated 12V supply). If that's the case then your options are: add an isolated DC-DC converter to generate the 12V, get a meter that doesn't need an isolated supply, or add a differential input circuit to the meter that can tolerate high common-mode voltage (72V).

 

[mrcshbs]

Still working on it

Hi…

Thanks for the help… the 12V meter does not have any problems at all.. show’s all the numbers fine.

The only problem is the 72V.

The 12V (positive and Negative) power the meter, then the positive and negative from the 72V battery bank goes to the input readings in the meter…

I have a RadioShack nearby here… is there any thing I need to add from the 72V ( + and -) going to the meter, like a diode or anything else that would eliminate this problem?

Can you send me like a part number or something? Or just tell me what I need to buy and I will ask the guy at RadioShack.

Thank you.

I really appreciate the help

Marcos.

 

[Leftyretro]

Hi,

My name is Marcos and I working on my first EV, the car is pretty much done, but there is only on problem.

I have added a 200V DC digital meter to the dash to monitor my 72V battery bank… the meter works fine when the car is first turned on, but as I press the accelerator and a load is applied to the big DC motor the goes displays some crazy numbers.. when I take my foot off the accelerator, the meter goes back to normal.

The meter has 4 wires in the back, 2 of them are a 12V isolated power supply.. and the other 2 are for the readings.

They are connected directly, I mean, the wires go from the meter to the battery bank and the 12V battery (power supply)

Is there any way I can correct that??

I have a cheap multi-meter I got from RadioShack, when I connect it, reads fine.. but this cheap meter also shows the meter when I accelerate the car as well…

Is there maybe a diode or some other device that I need to connect to this meter to make it work?

Please let me know

This is the meter I am trying to use (not the RadioShack multi-meter one)

Thank you.

Your drawing is showing the +72 volts going to both the controller's input and to the motor. Doesn't the controller have a seperate output going to the motor's positive lead? If your somehow measureing the PWM controller output instead of the 72 volt battery then that could explain maybe?

Do you have a link to a data sheet for your motor controller?

Lefty

 

[mrcshbs]

Hi...

the postive cable goes from the battery bank to the controler and also to the motor. just like it is in the drawing.

I use an alltrax 7245 - 72V - 450 amps controller.

 

[mrcshbs]

you know what... that could be it...

is there any way to "isolate" this meter from the controller, like a diode or something???

so instead of picking up noise from the controller or motor, it will only pick up the voltage from the battery??? even when it's all operational?

what do you think I need, capacitor?

it's a 72V battery bank, what kind of device do I need?

any help is appreciate it.

thanks

 

[ericgibbs]

you know what... that could be it...

is there any way to "isolate" this meter from the controller, like a diode or something???

so instead of picking up noise from the controller or motor, it will only pick up the voltage from the battery??? even when it's all operational?

what do you think I need, capacitor?

it's a 72V battery bank, what kind of device do I need?

any help is appreciate it.

thanks

hi,
The problem with a series diode filter it will reduce the true voltage reading by the forward drop of the diode.

I suppose you have routed the wiring for the 72V indicator away from the controller.

I would consider a balanced inductor filter with a capacitor on in and out ends of the filter.

 

[mrcshbs]

I know it's gonna sound really stupid...

where can I find these parts?

thanks

Marcos.

 

[ericgibbs]

I know it's gonna sound really stupid...

where can I find these parts?

thanks

Marcos.

this is the type of ready made unit I have in mind.

Car Audio Noise Suppressors | Pyramid #NS10 | Car Stereo Noise Filters

or EDIT:

**broken link removed**

 

[mrcshbs]

Great...


so all I need to do is buy 2 of these... connect them between the battery terminals and the meter input reading wires.. right?

are they polarity sensitive?

will they support 72V system or just 12V?

I changed the diagram to incorporate this device.. I am including with this reply.. please take a look at the battery terminals.. and see if this is correct. (on how to install them)

 

[ericgibbs]

Great...


so all I need to do is buy 2 of these... connect them between the battery terminals and the meter input reading wires.. right?

are they polarity sensitive?

will they support 72V system or just 12V?

I changed the diagram to incorporate this device.. I am including with this reply.. please take a look at the battery terminals.. and see if this is correct. (on how to install them)

hi,
I would mount them as close as possible to the 72V meter.
Regarding the working voltage, you will have to check with your auto shop, I cant see the Vrating on the spec.

This type is the one I would choose, it an overkill for the current, but its cheap.

If you had the skills you could make your own balanced filter, I would.
**broken link removed**

 

[Rolf]

LC Filter

Hi…

Thanks for the help… the 12V meter does not have any problems at all.. show’s all the numbers fine.

The only problem is the 72V.

The 12V (positive and Negative) power the meter, then the positive and negative from the 72V battery bank goes to the input readings in the meter…

I have a RadioShack nearby here… is there any thing I need to add from the 72V ( + and -) going to the meter, like a diode or anything else that would eliminate this problem?

Can you send me like a part number or something? Or just tell me what I need to buy and I will ask the guy at RadioShack.

Thank you.

I really appreciate the help

Marcos.

I would make a little LC filter like this:



Values are not critical but use powdered iron core inductor if available and a non electrolytic capacitor.
Connect close to meter.

 

[mrcshbs]

this one looks awesome

what are the parts I need to buy to make it?

do you know where I can find it? I mean, radioshack or do I have to go online to buy them?

thanks

 

[Leftyretro]

As a quite experiment you might want to run the + and - 72vdc meter input wiring right to the 72vdc battery terminals. The way you have it wired there is going to be lots of current flowing through the terminals you are presently using and that will effect the measurement because of the voltage drop variation.

Lefty

 

[Rolf]

LC Filter II

this one looks awesome

what are the parts I need to buy to make it?

do you know where I can find it? I mean, radioshack or do I have to go online to buy them?

thanks

Radio Shacks parts inventory is now close to pathetical.

Here is what I found, no guaranty it will work.

Get 2ea #273-102, 100UH RF choke. $1.39 ea and a 272-1055 1uf 250V metal-film capacitor $1.59.

If that dos not completely eliminate the noise then put more turns of wire on the chokes. Make sure they are wound in the same direction!

Or you might have to bite the bullet and buy a iron core (expensive) and wind your own chokes. Two windings on the same core should work.

 

[audioguru]

Some digital meters cannot measure a voltage that is part of its power supply.
Wasn't the meter that worked powered from an internal battery?