Can i hook only one side of a watt meter?

[rg12]

As you may know, all of those turnigy/cheap blue watt/volt meters (those that go up to 60v)
have 4 wires (red and black for load and red and black for source).

Is it possible to get all the readings correct if i connect only the Source side in the middle of my battery wires?
(scratch the wire insulations in the middle of the battery pack chord and solder the Source side of the watt meter).

Will it work? or do i have to connect both sides of the watt meter?

Roy.

 

[Punx0r]

No. The current must pass through the wattmeter for it to measure it. You can cut the wires in the middle of your pack and insert the wattmeter. It will still read current correctly, but the voltage (and wattage) will be halved.

 

[KINNINVIEKID]

They read the current etc on the negative wire as it passes through the meter from left to right so both these wires must be connected.
The red source wire must also be connected as that is where the meter gets its operating voltage from.
http://www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf

 

[rg12]

Thanks guys that helped

 

[teslanv]

To clarify a bit more: The negative (black) wire must pass through the watt-meter. The "Source" red wire can just tap into the positive wire to detect the voltage and power the unit. And the 60V limit is pretty hard. I just blew my second watt-meter by forgetting the voltage limit and plugging it into my 20A battery pack.

 

[dnmun]

where the wattmeter says source has to come from the P- spot on the BMS or the bottom of the battery of a lipo stack.

if you have a battery with higher than 60V then you can attach the red wire to the middle of your battery so you can keep track of a good estimate of total pack voltage by doubling that number.

you can power the wattmeter by using the auxiliary power input on the side and never use a connection on the red wire. so the wattmeter in that case only displays the Ah and not any voltages or Wh readings.

make sure there is a switch to turn off the power to the wattmeter either in the voltage tap or the auxiliary power lead.

 

[rg12]

where the wattmeter says source has to come from the P- spot on the BMS or the bottom of the battery of a lipo stack.

if you have a battery with higher than 60V then you can attach the red wire to the middle of your battery so you can keep track of a good estimate of total pack voltage by doubling that number.

you can power the wattmeter by using the auxiliary power input on the side and never use a connection on the red wire. so the wattmeter in that case only displays the Ah and not any voltages or Wh readings.

make sure there is a switch to turn off the power to the wattmeter either in the voltage tap or the auxiliary power lead.

That sounds very interesting...How exactly do i connect this thing to the auxiliary? can you explain with a bit more detail which wire goes where? and where do i get this auxiliary connector?

All i need is the Ah reading anyway, would i be able to do this in a 87v pack?

Thanks,
Roy.

 

[dnmun]

the auxiliary power input is on the outlet on the end. you can see the labels on the plastic.

 

[rg12]

Well, I think i solved many of the guys problems here:
http://www.ebay.com/itm/BATTERY-MONITOR-DC-99V-100A-LCD-DIGITAL-PANEL-AMP-VOLT-WATT-AMPERE-HOUR-METER-/230946855027?pt=Mess_Pr%C3%BCftechnik&hash=item35c5815873

99V 100A volt/watt meter, maybe even will be able to fit it in my 60v watt meter can who knows.

Thing is that it needs external power 9-24v...any ideas how to power it without adding separate batteries or using a huge DC/DC converter that can stand my pack's high current?

What about the fact that it has only two wires instead of four? how do i connect this?

Also a bit expensive but this volt/amp rating is very exotic to find in this familiar lcd format that we already know...It's not fun finding what you
want in a huge industrial cube version that needs a power supply of an airplane courier.

Roy.

 

[r3volved]

I'm pretty sure it would only need around 5v to power the screen...that's all the external power does is power the screen.

 

[rg12]

well it says 9-24 while this isn't the issue, i am more concerned about where to draw the power from instead of making
an annoying 3s pack to power it.

 

[r3volved]

If it's 9-24 then use a generic 9v

 

[rg12]

If it's 9-24 then use a generic 9v

How stupid can i be to forget that there are other types of batteries than lithium

 

[Punx0r]

A tiny dc-dc converter should do. I imagine it only needs around 100mA?

 

[rg12]

A tiny dc-dc converter should do. I imagine it only needs around 100mA?

I thought about it but if i route the wires from the whole pack to the little DC converter then it
will get high current and blow am i missing something here?

The max input voltage i found for a small DC converter is 60v (on ebay) and my pack will be well beyong that close to 90v

 

[dilkes]

you can power the wattmeter by using the auxiliary power input on the side and never use a connection on the red wire. .

What type of connector is it that is used to provide power via that aux power input?

 

[dnmun]

i just use a 9V battery on a two wire JST plug. it uses a lot of juice though so it will drain a 9V battery if left on. i just unsnap the connector on top of the 9V to turn it off.

 

[friendly1uk]

At near 90v some phone chargers will work. I don't know of one that will give you 9v though. Somebody might.

Perhaps the auxiliary supplies ground and loads ground need to be common. Then the meter could measure the positive wire rather than the neg as the 60/100s do. It's that or the 3rd small wire has found it's use. Because you can't just look at one conductor and know the pack voltage.

 

[rg12]

I decided to use a single 18650 cell connected to a DC/DC step up converter (3.7v will turn to 12v) and have that power my meter.