Mounting Turnigy Watt Meter

heathyoung · Jun 23, 2013

Metal film resistors are not ideal for use as shunt resistors - they suffer from localised heating and fail - ask me how I know that one

It wont happen immediatly, but the resistance value creeps over time (goes up).

dnmun · Jun 23, 2013

i already asked you how that charger worked and never found out. but i do know that the cheap watt meters use these surface mount 2512s for shunt resistors.

pdarnett · Jul 3, 2013

Been doing this mod myself this evening on one of the new meters (no calibration!) fear I've comprimised the shunt with too much solder. Shows 0.74A when actually drawing 3A! Anyone recommend a replacement shunt I can use? Preferably that I can get here in the UK?

d8veh · Jul 5, 2013

File the shunt to increase its resistance.

adrian_sm · Jul 5, 2013

d8veh said:
File the shunt to increase its resistance.

No don't. Check how acfurate it is at high amps first. I found they are quite inaccurate at low amps, and from memory worse once the shunt is remote.

Hwy89 · Jul 5, 2013

I have a brand new Turnigy 130A watt meter from Hobby King and I can't read the display. If I look straight at it all that is visable is rows of black squares. If I look from an extreme angle I can almost make out the numbers. The problem gets worse when I take it outside in the sunshine.
Is there a contrast or viewing angle adjustment inside? Should I try to fix it or just send it back to HK?

EVTodd · Jul 21, 2013

I finally got around to doing this mod on my meter. Super easy and works great!

Long overdue thanks to Jeremy!

MAGICPIE3FOCUSPOWER · Jul 23, 2013

I have given up with these meters... :mrgreen:

Voltage reading is okay, but current.... :lol:

So I have to spend money on real ones :oops:

dnmun · Jul 23, 2013

the one turnigy watt meter i still have that works is off by about 10% on the clock. the current calibration is definitely non linear. but close in the 15A range.

EVTodd · Jul 23, 2013

MAGICPIE3FOCUSPOWER said:
I have given up with these meters...
Voltage reading is okay, but current.... :lol:

So I have to spend money on real ones

I'm not sure how accurate it was originally but it has almost the same readings after the mod. I adjusted the voltage to match my multimeter. I still don't consider it exact by any means but it gives you some idea of what's going on with your setup.

MAGICPIE3FOCUSPOWER · Jul 23, 2013

Yup I always read the voltage, because current reading is.... :mrgreen:

O well I have ordered new one (4th) :lol: next time it will be a CA.

Tom L · Jan 10, 2014

I'm about to do this remote shunt mod and got the shunt off the PCB without any dramas but may have just stumbled on a problem.

I want to mount a power switch in the meter as per Jeremy's first post and have a subminiature toggle switch with a waterproof hood that fits in the space nicely but noticed that it is only rated for interrupting 28V DC. Considering I'm running a 48V battery is this likely to be a problem or will it be ok?

I suspect it will be ok as any arcing should extinguish fairly rapidly as it will be easy to cool such a low energy arc (the meter draws 3/5ths of f**ck all current).

dominator · Jan 10, 2014

May seem like a silly question but y do u need a watt meter, is it bc u dont have a cycle analyst?

Tom L · Jan 10, 2014

dnmun · Jan 10, 2014

Tom L said:
I'm about to do this remote shunt mod and got the shunt off the PCB without any dramas but may have just stumbled on a problem.

I want to mount a power switch in the meter as per Jeremy's first post and have a subminiature toggle switch with a waterproof hood that fits in the space nicely but noticed that it is only rated for interrupting 28V DC. Considering I'm running a 48V battery is this likely to be a problem or will it be ok?

I suspect it will be ok as any arcing should extinguish fairly rapidly as it will be easy to cool such a low energy arc (the meter draws 3/5ths of f**ck all current).

this should not be a problem since the wattmeter only uses about 160mA, mostly to drive the leds. you are not switching a large current.

you only need large wires where the shunt is located, the other wires, for the kelvin connection to the meter and the red power lead can be very small. 30AWG even.

Tom L · Jan 10, 2014

Yep I realise that. The problem is that switching DC off is difficult. The current isn't interrupted 50 or 60 times a second like AC and any arcing tends to be sustained. The very low current used to supply the meter however means that any arcing will be quite low energy and easily cooled and extinguished. This is what I found. My little 28V DC rated switch had no problem interrupting the hot off the charger battery voltage.

As for using 30AWG cable, that's not what I found. Initially I was using about 1.5m of 3 core 28AWG cable. With both (-)ve wires shorted to the battery (-)ve terminal (i.e. no shunt in circuit) I was getting a current reading of 7A. The loop resistance was too high. I changed to some 3 core mains flex (~15AWG) and the shorted measurement dropped to 0.7A. Good enough for me.

Result:

robert--76 · Mar 3, 2014

Just build my remote shunt Turnigy Watt Meter and it works fine! The only thing is the contrast of the display which gets worse over 35 volts. At 60 volts you cant read anything anymore... Does anyone know how I can adjust the contrast? Maybe by using a potmeter somewhere between the display?

d8veh · Mar 5, 2014

Here's one I did. I used approximately 6cm of 14g wire for the shunt rather than the original shunt. I calibrated it by changing the length to get the exact value. I also sealed all the holes to make it waterproof. Without the shunt inside, it no longer needs the ventilation holes:

dr_frost_dk · Mar 7, 2014

Just did this also with the old (still working fine) meter i used on the ciao and DM50 and now for my e-bike (will make thread about it soon

, done 500km so far) and it worked, well to start with i was locked at 137.??A like others complained about, but this was due to connection missing at output - connection, there is a very small pad that needs to be connected to the BIG pad, after that it worked as it should, tested with various POWER resistors and it is a few % of so good enough for my old meter that have survived 4 years, countless rides in rain and snow (WITHOUT ANY PROTECTION/MODIFICATION)

I used servo wire 22AWG like http://www.rctimer.com/product_928.html, about 1 Meter (3 feet), and it works just fine, will make a switch to turn off light, and also a cutoff to reset counter

Future "upgrades":
Make custom wire-shunt to get close to perfect accuracy

granolaboy · Apr 26, 2014

Hrm, I'm not sure this mod works unless you have the adjustment pots.

I just got a super cheapie watt meter like this one:

$(KGrHqN,!hcFC80Il!t9BQ9f9m21MQ~~60_12.JPG

Which has no adjustment pots. I removed the shunt resistors (had 3 0.003 mohm resistors), and did the mod and wired it all up with 3-4 feet of 16ga wire. Tested with a 18w bulb. No amps. Hrm...double-checked the external shunt soldering, no shorts. So I tried it on a 500w motor on the stand, and it peaks out at 2A...should peak out at more like 5-6A.

I put the shunt resistors back in the original spots and it reads 5-6A again.

My guess is that the resistance of the sense wires is dropping both source/load voltages, causing a reduction in the perceived voltage drop across the shunt...if I had those adjustment pots i could tweak it back.

Thought I'd post in case it saves anyone any hassles.

Maybe I'm on crack and something else is wrong, but my guess is watt meters like this one with no adjustment pots can't do the external shunt mod...

Tom L · Apr 26, 2014

granolaboy said:
My guess is that the resistance of the sense wires is dropping both source/load voltages, causing a reduction in the perceived voltage drop across the shunt...

I found the opposite:

Tom L said:
...Initially I was using about 1.5m of 3 core 28AWG cable. With both (-)ve wires shorted to the battery (-)ve terminal (i.e. no shunt in circuit) I was getting a current reading of 7A. The loop resistance was too high. I changed to some 3 core mains flex (~15AWG) and the shorted measurement dropped to 0.7A. Good enough for me.

Result:

d8veh · Apr 27, 2014

granolaboy said:
Hrm, I'm not sure this mod works unless you have the adjustment pots.

I just got a super cheapie watt meter like this one:

Which has no adjustment pots. I removed the shunt resistors (had 3 0.003 mohm resistors), and did the mod and wired it all up with 3-4 feet of 16ga wire. Tested with a 18w bulb. No amps. Hrm...double-checked the external shunt soldering, no shorts. So I tried it on a 500w motor on the stand, and it peaks out at 2A...should peak out at more like 5-6A.

I put the shunt resistors back in the original spots and it reads 5-6A again.

My guess is that the resistance of the sense wires is dropping both source/load voltages, causing a reduction in the perceived voltage drop across the shunt...if I had those adjustment pots i could tweak it back.

Thought I'd post in case it saves anyone any hassles.

Maybe I'm on crack and something else is wrong, but my guess is watt meters like this one with no adjustment pots can't do the external shunt mod...

i Think you're right about the thickness of the wires. I did the same meter with very thin wire and it showed no amps. I then used three-core servo wire and it worked perfectly.

granolaboy · Apr 28, 2014

yah, i tried it first with 28awg hookup wire, then switched to 16awg.

how thick do i need to go here? seems odd that other ppl are getting it to work with super tiny ethernet cabling...and that some are finding the sense wire resistance is adding to the shunt resistance, where as in my case it seems to be subtracting from it.

i'll try some thicker wire...maybe it's a shielding issue? i've also tried twisting the sense wires together, having them apart, etc...doesnt seem to make a difference.

dnmun · Apr 28, 2014

wire size makes no difference for the kelvin leads.

all the $13 wattmeters i have bot had the little trimpots inside. i have some new ones i never opened so i will look, but that is how i adjust and calibrate the shunt.

i am using a shunt from an old turnigy wattmeter i burned up and removed the 2512 surface mount resistor used for the shunt in the cheap one so i can read the current on the cheap meter using the turnigy wattmeter shunt.

i install the shunt between the B- spot on the BMS and the bottom of the battery.

granolaboy · Apr 28, 2014

dnmun said:
wire size makes no difference for the kelvin leads.

all the $13 wattmeters i have bot had the little trimpots inside. i have some new ones i never opened so i will look, but that is how i adjust and calibrate the shunt.

i am using a shunt from an old turnigy wattmeter i burned up and removed the 2512 surface mount resistor used for the shunt in the cheap one so i can read the current on the cheap meter using the turnigy wattmeter shunt.

i install the shunt between the B- spot on the BMS and the bottom of the battery.

thanks...my observations point to that fact as well (sense wire thickness makes no diff)

but i think without those pots, one has no way of getting it accurate.

i guess without the pots one could play with the shunt resistance to calibrate.

at the end of the day, a CA is what I want, and well worth the money, I'm just having fun hacking cheap tech

i have a 75a/75mv (1mohm) shunt on order so ill test with that as well.

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