SamTexas said:
A x V = Watt 
How can I mod this watt-meter?
- Thread starter ian.mich
- Start date
A x V = Watt SamTexas
1 MW
OK, no argument from me. But your $4 figure does not work anymore. You need not one, but two DMM. You also need a shunt so you can read the current on the second DMM. And your brain needs work superfast to convert whatever voltage you see on the "A" meter to actual current and multiply with V to get your power. Watch out, here come another truck!nicobie said:SamTexas said:
What can I say...
If you are looking for a cheap way to monitor your system, this will work.
If you are looking for a cheap CA, good luck
If you are looking for a cheap way to monitor your system, this will work.
If you are looking for a cheap CA, good luck
You can still use the originally-linked WM for your 100V+ pack, but in a way that doesnt' monitor watts or Wh or voltage quite right (yet is simple to recalculate).
Put a tap for the watt meter to go in on 1/2 your pack, so that it is only reading the voltage from half of it, keeping it under the likely 60V max even when fully charged.
Then just multiply the W, Wh, and voltage readings by two, and you'll have the correct numbers for those, within a reasonable accuracy.
The Amps and Ah will be correct either way.
http://www.endless-sphere.com/w/index.php/Setting_Up_a_Low-Voltage_Watt_Meter_for_a_High_Voltage_System
Put a tap for the watt meter to go in on 1/2 your pack, so that it is only reading the voltage from half of it, keeping it under the likely 60V max even when fully charged.
Then just multiply the W, Wh, and voltage readings by two, and you'll have the correct numbers for those, within a reasonable accuracy.
The Amps and Ah will be correct either way.
http://www.endless-sphere.com/w/index.php/Setting_Up_a_Low-Voltage_Watt_Meter_for_a_High_Voltage_System
rwaudio
100 mW
- Joined
- Apr 4, 2011
- Messages
- 46
amberwolf said:
That won't actually work as you describe. The best you could do is measure voltage of half the pack, but all other measurements are not possible. Current needs to flow through the meter so unless the OP is charging the pack with two separate isolated chargers each charging half the pack it doesn't work.
If it was a hall effect based device that could work, but these almost always use a shunt which you can't get in the current path at the 1/2 pack voltage point.
Current thru the series-wired system is the same at any point in the system, so regardless of where you put it, it'll still measure current accurately.
Besides, if you are using it on the "bottom" (most negative) half of the pack, the shunt is in the ground wire of most of these meters, so it would still read the full system current, exactly as if you were measuring the full pack--the only difference is that the voltage supply to the meter is only half the pack's voltage, if it's tapped in the middle of the pack.
You could use two meters, one on each pack half, and add the watt-based readings, but multiplying a single meter's results by two is close enough for most purposes, unless you truly need to monitor actual pack voltage sag and the like. Two meters cost nearly twice as much, too (slightly less as usually shipping cost isn't doubled), so depending on price and complication of setup it might wind up easier to buy a CA or something similar.
Besides, if you are using it on the "bottom" (most negative) half of the pack, the shunt is in the ground wire of most of these meters, so it would still read the full system current, exactly as if you were measuring the full pack--the only difference is that the voltage supply to the meter is only half the pack's voltage, if it's tapped in the middle of the pack.
You could use two meters, one on each pack half, and add the watt-based readings, but multiplying a single meter's results by two is close enough for most purposes, unless you truly need to monitor actual pack voltage sag and the like. Two meters cost nearly twice as much, too (slightly less as usually shipping cost isn't doubled), so depending on price and complication of setup it might wind up easier to buy a CA or something similar.
fivari
10 W
puddleglum said:
I've got one like these. It shows current, Voltage, Watt and Ah but does not allow to know how many Wh used. You could multiply the Ah with average voltage, if that is good enough for you.
Jeremy Harris
100 MW
Emoto said:Or buy one of these
i had the first metre good but prefer this one.
Won't do what the OP wants, unfortunately. He's looking for a wattmeter that will accept 100V, and the only one that I know of that will do that is the CA, as already mentioned earlier in this thread.
Yes 
your right, i should have elaborated, as you know there is a voltage mod for the turnigy but sadly only reads to 75v but working on 100v i think, http://endless-sphere.com/forums/viewtopic.php?f=31&t=17904. Is there a better mod thread jeramy ?
I would love to find a simple/cheaper watt-metre in the 100/120 v.
I wonder if enough of us contacted hobby king and requested a modified version of the turnigy to handle 150v/150amp that would be very popular.
your right, i should have elaborated, as you know there is a voltage mod for the turnigy but sadly only reads to 75v but working on 100v i think, http://endless-sphere.com/forums/viewtopic.php?f=31&t=17904. Is there a better mod thread jeramy ?I would love to find a simple/cheaper watt-metre in the 100/120 v.
I wonder if enough of us contacted hobby king and requested a modified version of the turnigy to handle 150v/150amp that would be very popular.
Jeremy Harris
100 MW
Emoto said:Yes
I would love to find a simple/cheaper watt-metre in the 100/120 v.
I wonder if enough of us contacted hobby king and requested a modified version of the turnigy to handle 150v/150amp that would be very popular.
I don't know of one, TBH, other than the CA. The main problem with getting up to voltages like this is the power supply for the unit, it would really need a small switched mode supply to run at 100 V plus. The changes to the resistive divider that senses the supply voltage is just a component value change, then the firmware would need to be altered to increase the range indicated. I doubt the volume of sales would be enough to get HK interested, plus there are legal issues as soon as you make something to sell that works at over around 60 V, as it then needs safety certification I believe.
Well the best i can find atm Ian is this volt metre http://endless-sphere.com/forums/viewtopic.php?f=14&t=40616 courtesy of dogman
and a promising volt amp and Ah meter for USD $15 http://endless-sphere.com/forums/viewtopic.php?f=14&t=40434&p=590861#p590861
the latter looks sweet
and a promising volt amp and Ah meter for USD $15 http://endless-sphere.com/forums/viewtopic.php?f=14&t=40434&p=590861#p590861
the latter looks sweet
eCue
10 kW
I picked up a inline watt meter on eBay used for RC battery charging / monitoring that seems well suited to ebikes. I tried to post a link but it did not take
here a link to a thread with a pic of one https://endless-sphere.com/forums/viewtopic.php?f=3&t=91384
here a link to a thread with a pic of one https://endless-sphere.com/forums/viewtopic.php?f=3&t=91384
