These wattmeters are all over Ebay and Amazon for about £10. They can tell you a lot about how your bike works and everything about your battery if only you could see it while riding. You could thick battery wires up to the hand lebars and back, but not only is that ugly, but you also get some power loss. Here's how to fix all that for almost zero extra cost. All you need is some three-core wire, thinnish, but not too thin - IIRC 22g or thicker is about right; a small piece of vero-board or something similar; a soldering iron; some solder; and a small phillips screwdriver.

 

First step unscrew the case. As you can see, it's the same as any of the others. It takes power from the incoming red and black. The red goes straight through. the black goes through an R0001 shunt and out the other side. The current is measured by the voltage drop from one side of the shunt to the other using Ohm's law Current = voltage drop divided by the resistor value. The power in watts are calculated from current times resistance, and the watt-hours are calculated by watts times time. There is a three-pin connector for testing servos, which we don't need. The shunt gets warm at high currents, so they provide ventillation slots at each end of the case:

 

Step 2 unsolder the wires and keep them.

 

Step 3 unsolder the shunt and cut off that 3-pin connector:

 

 

Step 4 solder on the three thin wires. The red goes to where the red wires were soldered, the plack goes to the IN side pad where a black was and the white goes to the other one. Tie a knot or put a zip-tie around the cable to stop it pulling out of the case:

 

Edited July 16, 20232 yr by saneagle

Step 5 Cut a small piece of vero-board or similar. Fill up the holes with solder and splash a load of solder on both sides where you want to solder the thick wires to. Solder on the shunt, making sure that there's definitely no connection between the two sides:

 

 

Step 6 Turn it over and solder the thin wires to the other side. red to red, black to black and white to black. It doesn't matter at this stage which way round you put the black and white:

 

 

Step 7 Solder on whatever connectors your battery uses to connect to the controller. You must make sure that the side with the white wire is on the controller/out side:

 

 

 

Step 8 Fill all the gaps and vents in the main part with silicone sealant and screw it back together. That button thing is not going to be waterproof, so it might be an idea to silicone that as well because you don't really need to change modes. It'll probably still work if you put a layer of silicone over it. You'll have to try it.

 

Step 9 Insulate the shunt with lots of electric tape, heatshrink or whatever you want. Now any time you want, you can clip this device in between your controller and battery to get all that useful information:

With this newer type of wattmeter, can you get it to display Wh instead of Ah? Is there a function for that, or is it fixed?

With this newer type of wattmeter, can you get it to display Wh instead of Ah? Is there a function for that, or is it fixed?

I'm not at home at the moment to check, but I'm pretty sure it does. When you press the button, there were pages of different things displayed. That includes highest current, highest voltage and things like that.

I'm not at home at the moment to check, but I'm pretty sure it does. When you press the button, there were pages of different things displayed. That includes highest current, highest voltage and things like that.

 

Ok, that's great, thanks

 

The one that I have is nice, but it remembers the Wh, even if disconnected. It says in the manual you can reset this by "a long press on the button", but all that seems to happen is that if the press is not long enough, it just turns the light on/off, yet too long and it goes into a voltage min/max alarm setting - bypassing the Wh reset option.

 

These programmable things with a single button are a nuisance!