I got one of these:
LED Digital Volt Amp 2 in 1 Panel Meter Voltmeter Ammeter 100V 100A Blue/Red
http://www.ebay.co.uk/itm/161224223929?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Costs about $5
It arrived a couple of days ago, and I was working with it today.
It will go up to 100 volts, and 100 amps; it needs a shunt. You can buy them (I ordered one), but it hasn't arrived yet, and, impatient to try out my new thing, I decided to make one. That turns out to be rather easy.
The shunt needs to be such that at 100amps, 75mv appears across the shunt. Ohms law says that means .75 milliohms. AWG 10 is 1 milliohms per foot, so I want 8 inches.
But how accurate is this? So I used my array of 50w, 12v lamps; when I power it from a 4S 20C, I get about 17 amps. I put that in series with a Hobbyking ammeter to determine the number of amps, then put my ammeter in series with that, and I tried various lengths of 10AWG until both meters read the same number (8 inches was about right). I wouldn't say that this is going to be tremendously accurate, but I'm just trying to keep an occasional eye on how much current the bike is using, I dont really mind if it's plus or minus an amp..
The meter wants a power supply of between 4.5 and 30v, so I decided not to take it from my main battery, which is slightly more than 30v (but would be a lot more if I decided to run it 12S, which I have tried, and which is pretty frisky. So I put a couple of AA batteries in a box with a little switch, and that sits with the main batteries. There's four wires that run from there to the front.
1) Common negative
2) Power for meter
3) +ve side of home-made shunt
4) +ve of battery
These four wire carry almost no current; I looked around my workshop for a four-conductor cable, and I'm using a couple of yards of ethernet (8 conductor) cable, and a plug-in connector so I can take the battery-and-shunt assembly off (that's built in to my saddlebag wattmeter/fuse/switch/main-battery-connector).
I'm just waiting now for a delivery of EC5 connectors so that I can solder up the final version of this, but it is working nicely.
LED Digital Volt Amp 2 in 1 Panel Meter Voltmeter Ammeter 100V 100A Blue/Red
http://www.ebay.co.uk/itm/161224223929?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649
Costs about $5
It arrived a couple of days ago, and I was working with it today.
It will go up to 100 volts, and 100 amps; it needs a shunt. You can buy them (I ordered one), but it hasn't arrived yet, and, impatient to try out my new thing, I decided to make one. That turns out to be rather easy.
The shunt needs to be such that at 100amps, 75mv appears across the shunt. Ohms law says that means .75 milliohms. AWG 10 is 1 milliohms per foot, so I want 8 inches.
But how accurate is this? So I used my array of 50w, 12v lamps; when I power it from a 4S 20C, I get about 17 amps. I put that in series with a Hobbyking ammeter to determine the number of amps, then put my ammeter in series with that, and I tried various lengths of 10AWG until both meters read the same number (8 inches was about right). I wouldn't say that this is going to be tremendously accurate, but I'm just trying to keep an occasional eye on how much current the bike is using, I dont really mind if it's plus or minus an amp..
The meter wants a power supply of between 4.5 and 30v, so I decided not to take it from my main battery, which is slightly more than 30v (but would be a lot more if I decided to run it 12S, which I have tried, and which is pretty frisky. So I put a couple of AA batteries in a box with a little switch, and that sits with the main batteries. There's four wires that run from there to the front.
1) Common negative
2) Power for meter
3) +ve side of home-made shunt
4) +ve of battery
These four wire carry almost no current; I looked around my workshop for a four-conductor cable, and I'm using a couple of yards of ethernet (8 conductor) cable, and a plug-in connector so I can take the battery-and-shunt assembly off (that's built in to my saddlebag wattmeter/fuse/switch/main-battery-connector).
I'm just waiting now for a delivery of EC5 connectors so that I can solder up the final version of this, but it is working nicely.