Remote Watt Meter for £13 or less

[Deleted member 4366]

I have done this mod successfully, so I thought I would share it. These watt meters cost only £10 each plus £8 postage for as many as you want. I bought three so they worked out at approx £13 each.
100A Balance Voltage Power Analyzer & Watt Meter -BC013 on eBay (end time 31-Dec-10 09:45:10 GMT)
The mod is base on the instruction by Jeremy Harris on the ES forum, so thanks Jeremy.
Endless-sphere.com • View topic - Mounting Turnigy Watt Meter
I've provided detailed photos with instructions under each one. Unfortunately they appear in reverse order so start on the last and then use the "previous" button above the first photo..
Remote Watt meter :: 11.jpg picture by d8veh - Photobucket

 

[z0mb13e]

I've been um'ing and ah'ing about creating my own power meter and perhaps open sourcing the whole thing - hardware and software - but the cost of shunts has been putting me off.

Any idea how accurate these meters are?

 

[Scimitar]

Now that's handy, and very cheap to do. Thanks.

 

[NRG]

Jeremy is a very clever chap. I built his simple fuel gauge, it works very well and is accurate enough for my use. It provides instant readout of battery draw and overall 'fuel' remaining. I went this route instead of the wattmeter as I don't need the continuous cycling numerical display of parameters or peak watts etc just what's left in the tank and when peak draw is happening. However implementing the wattmeter may be a lot simpler I suspect.

http://www.pedelecs.co.uk/forum/electric-bicycles/7208-e-bike-fuel-gauge.html?highlight=Meter

 

[wurly]

Very good, thanks for posting. Does that meter give a realtime reading at all times or do you have to press the buttons to select?
I like to glance at my turnigy meter occasionaly to see what power is being used. It cycles through whr's peak amps etc as well as giving realtime data. Not sure i'd like to take my hands off the handlebars to fiddle with the buttons.
What are those connecters you are using to connect to the shunt?

 

[Deleted member 4366]

It gives continuous real-time readouts of: volts; amps; watts; amp hours on the main display - as shown in the photo. It comes on to it's home screen as soon as you switch on the power, then you have to push one button before starting your journey. If you switch off the power, it resets, so you have to decide whether to put it before or after the main switch. It has other displays for checking and balancing lilos. lipos and lifepos.

To answer Z0mb13e's question about accuracy, the only thing I can say is that it's accurate enough. Without independent calibration equipment, it's not possible to determine the accuracy, but I don't have any reason not to believe what's shown in the display.

 

[Scimitar]

It has other displays for checking and balancing lilos. lipos and lifepos.

I'm definitely buying one now - my lilo keeps tipping me off.

 

[z0mb13e]

To answer Z0mb13e's question about accuracy, the only thing I can say is that it's accurate enough. Without independent calibration equipment, it's not possible to determine the accuracy, but I don't have any reason not to believe what's shown in the display.

Did it come with a manual? Is there a specs section? I was wondering if there was something along the lines of +/- 1% (either with or without a given watt and or temperature range).

All the shunts I have seen cost more than this meter!

I did consider the cheap option of just using a length of copper wire of a given guage but I don't have an Ohm meter accurate enough to calibrate or verify the kind of resistances needed for the power range we would likely need for an ebike. (Quite often a length of copper wire used as a shunt is pinched or squashed to alter its resistance as it can vary a lot)

I wanted a nice graphic lcd screen ( like this ) that can show bar graphs of power, voltage, estimated remaining battery capacity, speed etc and datalog stuff - ideally onto SD cards so you can actually see how your battery performs in real life over its life. Perhaps even plot graphs on screen.

That said £13 for a ready built meter sounds like a much cheaper and easier option

 

[Deleted member 4366]

I wouldn't get too hung up about the accuracy of this meter. The voltage readings for total and individual cells seems to be very precise and accurate and ties up with other equipment that I have, but I suspect that current, watts and amp hours are approximate. As I said before, I have no precise way of checking, but the meter does give consistant results, which is the most important thing. You only need to run your battery flat once from fully charged and then you will see how many amp hours the meter is showing. From there you can do a self-calibration in your head. It doesn't really matter whether it shows 8, 10 or 12 ah as long as you know at which point your battery will be flat.
Now that I'm switching to lipos, I find the meter even more useful because it can also show all the individual cell voltages in real time, which is important because I don't have a battery management system (BMS). I've just ordered a couple of these to see how they perform:
Lipo Battery Voltage Tester 1S-8S link Low Buzzer Alarm on eBay (end time 29-Jan-11 16:11:46 GMT)

 

[mxer125]

Dug deep for this one Great thread.......Was hoping to find your remote shunt thread pictures in reverse but they seam to have gone Any help with this d8veh ???........Thanks in advance

 

[Sacko]

I would be careful with this mod now. It looked spot on at the time, but unfortunately Hobbyking have changed the boards in them Watt meters so they do not have the pots anymore.

When I done my mod, the current reading was massively out.

 

[Old_Dave]

Yep the lack of pots is a pita, however as the 'current' is only a voltage reading of the difference between the ends of the shunt, I'd have a look at how much solder is shorting the shunt / using thicker wire to the remote shunt (less voltage drop) / or removing some metal from the shunt it self


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[mxer125]

Thanks for the advice but i wasn't thinking of ripping my Turnigy apart , just the cheapo £10 ones

 

[Deleted member 4366]

Dug deep for this one Great thread.......Was hoping to find your remote shunt thread pictures in reverse but they seam to have gone Any help with this d8veh ???........Thanks in advance

Watt Meter Photos by d8veh | Photobucket

 

[mxer125]

You are a STAR!!!!.... Thank you very very much d8veh!!!.

Just got to wait for mine to arrive now.

 

[Deleted member 4366]

I've had a couple of failures on the solder joints of the early ones I did, so I now solder everything to a bit of copper clad GRP that you can get from Maplin. This makes everything more rigid and manageable. Insulate the assembly afterwards with pvc tape or heat-shrink.
Copper Clad Boards : Printed Circuit Boards : Maplin Electronics

You then grind off copper to the pattern below with a Dremmel or file, drill holes for the two shunts, and solder Deans connectors directly to the copper, or you could solder thick wires. Whatever you use, there should be a male on the battery side and female on the other.

 

[mxer125]

Really amazing stuff d8veh, Can't Thank You enough.....

I'll let you know how i get on......