Ammeter on my handlebars

[drsolly]

I'd quite like an ammeter on my handlebars, but I don't want to run four 10AWG cables up from the battery to the handlebars to be able to use one of these http://hobbyking.com/hobbyking/stor...ompact_30A_Watt_Meter_and_Power_Analyzer.html

So I did a bit of sniffing around Ebay. Most of the ammeters that will read up to 100 amps, actually read a lot less, and are used in conjunction with an external shunt. I was thinking, that's a slightly messy disadvantage, and then I realised, no it isn't, it's a big plus!

So I ordered one of these http://www.ebay.co.uk/itm/201034251...eName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 and one of these http://www.ebay.co.uk/itm/291076410694?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 and for £6.03, I think I've bought myself a handlebar mountable ammeter that means that I only need two wires to the handlebars, and they can be 22 AWG.

 

[Tench]

Plus you will need a power source for the meter so it can function and display those amps.

Why not just fit a Cycle Analyst?

 

[drsolly]

Plus you will need a power source for the meter so it can function and display those amps.

Why not just fit a Cycle Analyst?

Power source can be a button battery. Or, since I'm running 8S Lipo, can be the bike battery.

Cycle Analyst = $125. CA has a TON more features, but most of them I can't use anyway. This ammeter = £6. I already have a voltmeter (about £2) and a speedometer (about £3). And I have five e-bikes ...

 

[dogman dan]

Somewhere there is a thread on how to hack a remote shunt onto the cheap wattmeters.

 

[Ykick]

There's likely other ways to do it but whenever I've used a remote shunt it's connected to a volt meter which utilizes voltage drop across the shunt resistance to render an Ampere value.

 

[drsolly]

That's how this one does it. My understanding is that when 100 amps flows through the shunt, the resistance is such that there's 75 millivolts (which means the resistance is 0.75 milliohm and the power consumption of the shunt is 7.5 milliwatts). Then the meter measures the voltage across the shunt. I don't know how many amps goes from the shunt to the meter. I'll use a clamp meter to check that.

I did see the thread about hacking a remote shunt onto a cheap wattmeter, but my solution is about $10, about the same as the cheap wattmeter, and I'm guessing it's a lot easier than the hacking job I'd need to so on the cheap wattmeter. Desoldering is not my forte.

I've also found this combination voltmeter and ammeter:

http://www.ebay.co.uk/itm/161224223929?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Which together with this shunt:

http://www.ebay.co.uk/itm/350782466265?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

costs £6.06 ($10 ish) and gives me volts and amps on one handlebar display. Which is all that I really need (plus a speedometer and a cheap cumulative wattmeter at the battery end, so I can look at how many amp-hours I used when I change battery).

There's a lot of ways to skin this particular cat

 

[dnmun]

you can follow jeremy harris's thread on remoting the shunt for the wattmeter. you can insert the shunt in the power lead from the BMS and run the kelvin taps up to the spot on the wattmeter pcb where you removed the shunt.

you can even put the kelvin leads on a reversible two pin plug so that you can reverse the plug and measure current into the battery when charging, if you mount the shunt in the B- lead from the BMS instead of the P- lead to the controller.

the kelvin leads from the shunt up to the wattmeter display can be tiny, 26 gauge wires since they carry no current.

 

[d8veh]

The cheap wattmeters are better because they tell you voltage and how many amp-hours or watt-hours you've used. It's very easy to rip out the internal shunt and make your own external shunt out of 12g or 14g wire. I've done most types. Here's my write-up:

http://www.pedelecs.co.uk/forum/threads/the-best-value-wattmeter.16869/#post-209920

 

[drsolly]

Interesting. I might try that. I have a suitable wattmeter, I'll take it apart and have a look inside.

 

[XLR8]

One thing to be aware of is that some digital ammeter displays are difficult to read in daylight. I have had a volt meter and an ammeter on my bike and both were very hard to read in full sunlght.

 

[dnmun]

i have a roll of the 4 milliohm surface mount resistors used in the shunt on the cheap wattmeters. it would take 4 of the 4 milliohm to make 1 milliohm and you could just make your shunt instead of moving that one, except it has to be removed to function as a kelvin tap.

 

[drsolly]

I took my cheap wattmeter apart and had a look inside. I can see the shunt, but I'm not so good with a soldering iron that I'd fancy the job of desoldering it, plus the access to it is very limited unless I desolder and remove the display first. So I'll stick with my plan.

 

[d8veh]

You don't hsve to desolder the LCD. Just bend it up out of the way.

Look at the photos in the link in my post #8.

 

[drsolly]

OK, I'll have another look, thanks for encouraging me!

And since I've led a separate 5v power source up to the handlebars, I could use that to power the meter so that when I switch off to leave the bike for several minutes, it retains the AH cumulative total.