power meter question

Hello,

I'm thinking to buy one of these power meter
http://www.ebay.co.uk/itm/5i-n1-DC100V30A-digital-combo-meter-LCD-backlight-volt-amp-kWh-watt-running-time-/251325754428?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3a842eac3c

or this one:
http://www.ebay.co.uk/itm/DC10-90V-50A-Dual-LED-Display-Digital-Voltmeter-Ammeter-Voltage-AMP-Power-Meter-/261184049199?pt=LH_DefaultDomain_0&hash=item3ccfc8502f


I'd like to use the same battery pack to power it via a 12V transformer:
http://www.ebay.co.uk/itm/24V-36V-48V-60V-72V-To-12V-Converter-Adapter-for-Battery-of-Electric-Vehicle-/390612438473?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5af250cdc9


Would it work or would it create some sort of short because it's the same battery pack?

Thanks

Why not just buy something designed for what you want that doesn't require a separate power source. Something like one of these.
http://www.ebay.com/itm/High-Precision-G-T-Power-RC-Watt-Meter-Tester-and-Power-Analyzer-130-Amps-/380644150825

because these ones are limited to 60V.

I use 84V 30A power.

Cheap enough to plug one in, and tell us if it shorts.

One option for monitoring an 84v pack with a 60v meter, is to just monitor half of it, then multiply all values by 2 except for Ah.

Here is where we say "Get a Cycleananlyst, you will love it."

cwah said:

I'm thinking to buy one of these power meter
...
or this one:
http://www.ebay.co.uk/itm/DC10-90V-50A-Dual-LED-Display-Digital-Voltmeter-Ammeter-Voltage-AMP-Power-Meter-/261184049199?pt=LH_DefaultDomain_0&hash=item3ccfc8502f

I'd like to use the same battery pack to power it via a 12V transformer:
http://www.ebay.co.uk/itm/24V-36V-48V-60V-72V-To-12V-Converter-Adapter-for-Battery-of-Electric-Vehicle-/390612438473?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item5af250cdc9

Click to expand...

There's a thread about these meters. This post has a PDF that shows ways to hook it up. There are so many knock-offs and variations that it's hard to be certain - but it looks like you should be fine since the DC/DC converter you selected has a common ground with the measured voltage. (That's a big converter - hope you have some other uses for all that amperage....)

you should buy a cycle analyst if you wanna know at high voltage. get useful info that stays after the BMS shuts off.

teklektik said:

There's a thread about these meters. This post has a PDF that shows ways to hook it up. There are so many knock-offs and variations that it's hard to be certain - but it looks like you should be fine since the DC/DC converter you selected has a common ground with the measured voltage. (That's a big converter - hope you have some other uses for all that amperage....)

Click to expand...

Thanks I'm looking at it

dnmun said:

you should buy a cycle analyst if you wanna know at high voltage. get useful info that stays after the BMS shuts off.

Click to expand...

I actually have one but it broke after 1 year. It's also quite bulky. All I need is to know how much power it used so this one seems best for my need. It's also smaller.

Ah - found it! Here's a series of posts that discusses using a common ground approach - this is the setup I tested.

The meter I got that was referenced in the PDF above was slightly different with an outboard shunt and terminal strip, but just appeared to be an embellishment on the simpler unit with internal shunt. I just used the 'three wire' system and tied the negatives together. Worked fine.

cwah said:

dnmun said:

you should buy a cycle analyst if you wanna know at high voltage. get useful info that stays after the BMS shuts off.

Click to expand...

I actually have one but it broke after 1 year. It's also quite bulky. All I need is to know how much power it used so this one seems best for my need. It's also smaller.

Click to expand...

What was the failure? I'm interested because we usually don't here about these things

Failure on the cycle analyst was on the keypad. It's still working. But the right key isn't working anymore.

I'm using for now the 90V 20A model with my brompton:


Here it is attached to the bag:


Hope this one will handle the power (I peak at 30A)... otherwise I'll have to get one with external shunt

I am using the same as cwah for checking my charging. No need for a separate 12V power source. The high voltage of the battery is taking care of powering the meter