Mounting Turnigy Watt Meter

[adrian_sm]

I was too lazy to remove the screen, and managed to remove the shunt without that step.

Still took a while though...

 

[SamTexas]

Instead of relocating the shunt, how about replacing it with an external one? Removing the shunt appears to be quite time consuming. The external shunt can just be a 6 5/8" long of #8 stranded copper. Just a thought.

http://www.motorcycleproject.com/motorcycle/text/shunt.html

The high current shunt works through a simple but elegant application of Ohm's Law. It has exactly 1/1000 (0.001) ohm of resistance. As a result, every 1/1000 (0.001) volt drop across its length equals 1 amp of current. The best part is that the shunt is ridiculously easy to make yourself. Simply solder a Mueller #27 alligator clip to each end of a piece of #8 stranded copper wire. But be very careful about the following three specifics. First, the wire must be #8 stranded copper, available at any home improvement center, and the Mueller #27 alligator clips must be carefully soldered so that the solder does not wick up the wire. This is critical, as it affects the tool’s resistance and therefore its accuracy. Finally, the shunt’s length from clip to clip (not end to end) must be exactly 6 5/8". This is important, as an error of only a quarter inch will throw off the tool’s readability. Coil the shunt after it is assembled to make it more compact.

Sam

 

[Jeremy Harris]

Instead of relocating the shunt, how about replacing it with an external one? Removing the shunt appears to be quite time consuming. The external shunt can just be a 6 5/8" long of #8 stranded copper. Just a thought.

http://www.motorcycleproject.com/motorcycle/text/shunt.html

The high current shunt works through a simple but elegant application of Ohm's Law. It has exactly 1/1000 (0.001) ohm of resistance. As a result, every 1/1000 (0.001) volt drop across its length equals 1 amp of current. The best part is that the shunt is ridiculously easy to make yourself. Simply solder a Mueller #27 alligator clip to each end of a piece of #8 stranded copper wire. But be very careful about the following three specifics. First, the wire must be #8 stranded copper, available at any home improvement center, and the Mueller #27 alligator clips must be carefully soldered so that the solder does not wick up the wire. This is critical, as it affects the tool’s resistance and therefore its accuracy. Finally, the shunt’s length from clip to clip (not end to end) must be exactly 6 5/8". This is important, as an error of only a quarter inch will throw off the tool’s readability. Coil the shunt after it is assembled to make it more compact.

Sam

The existing shunt has to be removed to enable an external shunt to work, as there is no other easy way to break the connections it makes with the sensing circuit on the board. If you leave it there, then it will just effectively short out the new remote shunt and cause high currents to flow up the connecting wires to the meter.

Using copper wire as a shunt is an incredibly bad idea. The reason has to do with the very low resistance of the shunt, 0.001 ohms in this case, and the way that copper wire resistance changes markedly with temperature. Add in that it is very difficult to measure resistances this low and the whole concept of a DIY copper wire shunt that is in any way usably accurate is pretty flawed. The shunts used in these really cheap meters are made from Constantan, and alloy with a very low resistance temperature coefficient. The resistance tolerance of the standard shunt is 1%, much better than you could hope to make with a bit of wire cut to length.

As an example, to get 0.001 ohms requires wire of an exactly known resistance per unit length. This varies markedly from one manufacturer, or even batch, of wire to another, certainly 8g wire can be anything from around 0.0006 to 0.0007 ohms per foot at 20 deg C, so you're starting off with an in-built error of up to around 15%, at a constant temperature of 20 deg C.

Now, add in the effect of temperature error, which will increase the resistance of a bit of copper wire by just over 5% for a change of just 15 deg C, from 20 deg C to 35 deg C, and you get total errors with the copper wire shunt system suggested of around 20% or so. If the wire temperature varies by more than 15 deg C, then the errors will be greater. This sort of error is unacceptably large, particularly when it impacts so massively on the cumulative Ah reading on the meter.

Getting the shunt off the circuit board isn't that hard to do, anyway. I took the display board off to get easier access, but as others have shown that isn't really needed.

Jeremy

 

[adrian_sm]

Removing the shunt appears to be quite time consuming.

Getting the shunt off the circuit board isn't that hard to do, anyway. I took the display board off to get easier access, but as others have shown that isn't really needed.

Getting the shunt off was actually pretty quick. I did it without removing the display. Most of my time was spent on all the new wiring, termination, heatshrinking etc. Things you would have to do no matter what shunt you use.

To get the shunt out I just let my soldering iron pick up most of the excess solder around each pad, took a couple of goes for each pad. Then sort of pushed the shunt sideways with the soldering iron, first from the left, then right, then left, etc. This let the heat melt the solder between the shunt and PCB on each side, until it was free to move. Done.

- Adrian

 

[SamTexas]

Using copper wire as a shunt is an incredibly bad idea. The reason has to do with the very low resistance of the shunt, 0.001 ohms in this case, and the way that copper wire resistance changes markedly with temperature. Add in that it is very difficult to measure resistances this low and the whole concept of a DIY copper wire shunt that is in any way usably accurate is pretty flawed. The shunts used in these really cheap meters are made from Constantan, and alloy with a very low resistance temperature coefficient. The resistance tolerance of the standard shunt is 1%, much better than you could hope to make with a bit of wire cut to length.

As an example, to get 0.001 ohms requires wire of an exactly known resistance per unit length. This varies markedly from one manufacturer, or even batch, of wire to another, certainly 8g wire can be anything from around 0.0006 to 0.0007 ohms per foot at 20 deg C, so you're starting off with an in-built error of up to around 15%, at a constant temperature of 20 deg C.

Now, add in the effect of temperature error, which will increase the resistance of a bit of copper wire by just over 5% for a change of just 15 deg C, from 20 deg C to 35 deg C, and you get total errors with the copper wire shunt system suggested of around 20% or so. If the wire temperature varies by more than 15 deg C, then the errors will be greater. This sort of error is unacceptably large, particularly when it impacts so massively on the cumulative Ah reading on the meter.

Jeremy

Ok, forget the copper wire shunt.

Getting the shunt off was actually pretty quick. I did it without removing the display. Most of my time was spent on all the new wiring, termination, heatshrinking etc. Things you would have to do no matter what shunt you use.

To get the shunt out I just let my soldering iron pick up most of the excess solder around each pad, took a couple of goes for each pad. Then sort of pushed the shunt sideways with the soldering iron, first from the left, then right, then left, etc. This let the heat melt the solder between the shunt and PCB on each side, until it was free to move. Done.

- Adrian

Great! I'll try it that way.

 

[adrian_sm]

Back on topic.

Now that I have a remote shunt, I moved on to making a mount for the handlebars or stem.

I repurposed one of these cheap rubber and velcro strap flash light mounts, trimmed a bit off it to create a flatter mounting surface, drilled a small hole, in the middle, similar small hole in the back case of the watt meter to accept a M5 pan-head screw. Then put it together with a couple of washers, and a nylock nut.

Easy to install & remove. Can fit a wide range of diameters/shape tubes. Works on bars or stem.
Works for me.

Here's how it turned out:



- Adrian

 

[Mark F]

Thanks for the help Jeremy.

I know this is the E-Bike section but I thought I would post some photos of a Turnigy Watt Meter modification for my sailboat here. If it wasn't for this thread I would have never known to do what Jeremy did. I hardwired my meter so there are no connectors. The power for the meter is supplied from the positive terminal on the controller so it turns on when the key is switched on. I'm really pleased.

I used this shunt; http://www.altestore.com/store/Meters-Communications-Site-Analysis/Shunts/100A-100Mv-Shunt/p4637/

Mark
Santa Cruz CA

 

[jmmorgan]

I tryed the remote mounting of the shunt, but now it will not read any amps. I have checked the wires and they are in the correct order. It reads the voltage fine, but no amps. Any thoughts on how I can trouble shoot this problem?
Thanks
John

 

[adrian_sm]

Two things I would check are:
1) current direction
- the meter only reads the current in one direction, try connecting you battery on the other side of the shunt, and see if that works
2) Calibration
- I had to adjust one of the little blue pots to get the current reading right. See this post for which is which. Of course you will need somethign to calibrate it against. I used my CA or multimeter during a battery charge, which provided a nice stable reading.

Good luck.

 

[Mark F]

Hi John,

Like Adrian wrote the shunt/ meter wires are probably reversed. Try switching them. I just added a switch to my watt meter modification so I can switch between motoring monitoring and regeneration/charging monitoring. I wanted to be able to see current for regen. If it is set to detect regeneration I cannot see any amps while motoring.

Mark

 

[jmmorgan]

Mark:
I tried switching the leads, but that did not work. Does anyone have a schematic of the circuit to help me trouble shoot the meter.
Thanks
John

 

[Wattever]

Are you using an old (more than 3 months ago) turnigy wattmeter, the old ones does not have pots and has two isolated peds under each shunt's leg- the shunt shorts theses peds when it is soldered on top of them, when you remove the shunt the larger ped does not reach the micro. if that is the case you just need to short them with soldering iron.

 

[jmmorgan]

It is the new meter. Unfortunately, there is no way for me to trouble shoot it. Live and learn.
John

 

[adrian_sm]

Mark:
I tried switching the leads, but that did not work. Does anyone have a schematic of the circuit to help me trouble shoot the meter.
Thanks
John

Here is a schematic for the wattsup meter, which the turnigy watt meter is a clone of. There are a few discrepencies, but it is very clsoe.
http://endless-sphere.com/forums/viewtopic.php?f=3&t=13607&p=242804#p242804

 

[Metallover]

I just attempted this mod. I ripped off a couple solder pads when I was taking the boards apart. I tried my best to save the connections, and the screen still works. The only problem is that I'm getting 137.37a. The voltage is accurate and changing the voltage doesn't effect the amp reading. Running current through the shunt doesn't effect the amp reading either.

I have everything wired correctly. There was a small blob of solder near the shunt that I removed and it didn't effect the reading at all. Maybe I overheated the board when I was removing the shunt? Maybe messing up the screen is effecting the readout? I do not have pots in my meter to calibrate it.

 

[adrian_sm]

Got any pics of the damaged bit of the board. Sounds like the current sense track is being pulled high, but these tracks are over near the shunt, not near the display you were desoldering.
Did you try to remove the shunt as well?

 

[Metallover]

I did remove the shunt. It took me a pretty long to take it off, and I was somewhat careful not to let anything get too hot. I could have damaged something tho...

The only picture I have is of the red board right after I separated the boards. I didn't remove the shunt yet- http://i345.photobucket.com/albums/p382/metallover1/IMG_0529.jpg

 

[adrian_sm]

Hmm. That makes it hard. Where was the small blob of solder you removed? Which solder pads did you damage? If you can point to it on one of the photos of the PCB floating around, we might be able to help.

Here are a couple of reference images
Image 1 - PCB Back
Image 2 - PCB Front
Image 3 - Newer Watt Meter PCB
Watt's Up Schematic

FYI I ended up connecting my remote shunt to two via holes on the accessbile "back" side of the PCB, just above where the red wire used to be solderd on.

 

[Metallover]

I appreciate your help! I broke out the macro camera and took a few pictures. They are all directly linked.

The first two show the shunt and my solder mess. Now that I look at it, it is a lot of solder! :| The third picture shows the damaged pads. One is in the middle and one is on the right. I cleaned up the one on the right so now it is not grounded to the screw hole, although I think they are on the same trace.

 

[adrian_sm]

Looks okay so far. How about where the current sense wires connect to the main PCB.

 

[Metallover]

Well crap. Better put a new watt meter on my list! I was messing around with it and the battery lead shorted out on the screen. It made a nice healthy pop.

Now when I plug it in the screen turns blue and it starts hissing at me. That's when I unplug it.

I took a couple more pictures anyway.. One again it looks like I did a crappy job soldering the wires onto the board. I think I should have used more solder.. But the second picture shows damage from the short- nothing looks destroyed on the board it just doesn't work.



And once again, I appreciate you helping me! Sorry I ruined the meter lol

 

[adrian_sm]

Ah shite. That sucks.

You might be interested to know I managed to do the remote shunt mod without seperating the boards. I removed the main leads fairly easily holding it upside down to make sure the solder didn't fall in where it shouldn't. Then I just short of pushed the shunt sideways alternating sides while heating up the solder until it broke free. It was actually pretty quick to do, I just don't have the patience to remove the screen. I knew I would just botch it up. :lol:

 

[Metallover]

Good to know for when I get my next one lol! Playing with the old one it seems like bending the boards apart doesn't do too much damage. It took me 4-5 90* bends to damage/break a few pins. I'll probably end up bending it just a little if I need to get my iron in there. Perfect!

 

[Mark F]

I also did not separate the boards. Here is what I did to remove the shunt.

 

[Wattever]

View attachment DSCN0543.jpg

this is why you did not get current readings, the high end of the shunt wire should touch the little square pad