Go to content Go to navigation Go to search
Welcome to the Electric Car Weblog. In addition to links, news, and tips about electric cars and other forms of alternative transportation we are publishing an on-line diary of our current EV project. Started in August 2005 the chronicle follows the conversion of a gas powered Ford Probe into an Electric Car.

You will find articles organized by categories, along with recent comments, along the right hand column of the website. If you are just getting started with the idea of converting a gas car to electric be sure to check out Your First Electric Car

Welcome and enjoy!

Meters · 30 November 05


With the first EV I used this E-Meter from Cruising Equipment. It shows volts, amps, amp hours, and time remaining…but only one at a time.

Along the top of the meter is a little “gas gauge” which shows approximately how much charge is left in the battery pack. It’s a rough, well, very rough estimate and can have some serious lag.

The other downside is that you can only see one reading at a time. To toggle between volts and amps takes from 1 to 4 presses of the SET button.

I’ve started thinking about what to use for Eve. Easiest approach is to pop the E-meter in again and leave it at that. Maybe add an analog meter for showing the current or voltage, so the meter can be left on one position most of the time.

EVDash on Palm Z22

A couple weeks back I bought a new Palm Z22 for 99 bucks. I gave my last Palm to Dad a few years ago when I changed jobs thinking I didn’t need it. I really missed it, since it acts as a backup brain.

Searching for software (hex calculator, password manager, adobe reader) I stumbled across Ohler’s site.

What a great resource! He’s owned a few EVs (be sure to check out the Spyder and its schematic) and has written a couple of Palm EV apps. The one shown here, EVDash, hooks to an E-Meter with the optional RS-232 connector. This allows the Palm to show volts and amps, along with overall capacity based on both.

Great, I’ll use that!

A couple problems. #1, the Z22 is USB, not serial, so you need an older Palm model to take advantage of this. #2, my E-Meter doesn’t have the RS-232 option.

We probably have an ancient palm kicking around somewhere, and there’s always ebay, so that problem is solvable. Cruising Equipment was purchased by Xantrex and the meter is now called a Link10. Not sure if they still make it and my email to support asking about an RS-232 upgrade has so far gone unanswered.

Another option is to make my own. I’ve been learning embedded system programming and this might be within my grasp, especially since I work with smart folks that’ll answer newbie questions.

Analog Amp Meter

I could probably install a couple analog meters. They are very responsive and it’s faster to glance at these meters to quickly assess readings. The only downside is they typically take more room and, franky, are a little “hobby ugly.”

If I end up using AGM batteries the car will need some sort of battery management system. Lee Hart has posted a do-it-yourself battery balancer. He also had posted another idea that you can read about at the bottom of Cameron’s Battery Management page.

Comments 26
  1. — Jody Dewey    Jan 06, 2006 21:15 PM    #
    If you are looking for a cheap palm solution for a gage Palm IIIe ones are available for $20 from www.surpluscomputers.com
  2. Jerry    Jan 08, 2006 10:03 AM    #
    Thanks for the tip Jody!
  3. — James May    Jan 11, 2006 10:05 AM    #
    I’m trying to order a hobby kit tachometer for my car. The Velleman K2625. It's a simple, continuously calibratable 2 figure revcounter which I am hoping to attach to the hall effect sensor on the end of my motor. To stop me overrevving it you see!
  4. — Mesuge    Jan 14, 2006 18:09 PM    #
    Has anybody thought about hooking Ohler’s EV Dash soft with some basic circuit which will meassure and send data via serial cable/protocol? I’ve asked Ohler about it and it is indeed doable his soft needs only three simple input values amp,volt, time.. Btw. there is datasheet for E-meter at the manuf. website and the proper data format is explained there..

    Thanks for any info on that!
  5. Jerry Halstead    Jan 15, 2006 11:08 AM    #
    Howdy Mesuge,

    That’s a good idea for someone with the electronics skills and/or hacker buddies.

    Do you have a link for the e-meter data spec? I found the user docs but didn’t see the rs232 data format.

  6. — James May    Jan 15, 2006 13:56 PM    #
    Its in here I think
  7. Jerry Halstead    Jan 15, 2006 14:14 PM    #
    Right you are (RTWFM Jerry)!

    James, to turn a URL into a clickable link put quotes around the text that you want linked, immediately followed by a colon and the url.

    The Textile Help link right below the comment box has an example.

    Hmm, should links in the articles be red like they are in the navigation bar?
  8. — Mesuge    Jan 16, 2006 19:22 PM    #
    I do have some additional information about the data stream needed – one guy was using E-meter/EVdash format for solar panel diagnostics. The data output from this device is very simple just 10 values divided by a comma which are being send via serial port to the EVDash program which in turn takes only 2 of them (voltage & current) and calculates the rest.

    You can see the details about required data format (ASCII 9600 8N1) output from Xantrex and how to connect it with PC here in this solar charging measurement application: PDF File

    Link to Mr. Ohler’s EVDash software
    Voltage – Battery pack voltage.

    Amps – Amps being drawn from or put back into the battery pack.

    Capacity based on voltage – Capacity calculated from the pack voltage under very low load. Voltage drops off as pack capacity drops.

    Capacity based on amps – Capacity calculated from the amps drawn integrated over time compared to the pack capacity. The peukert effect is taken into account.

    Baud rate: 9600, Data bits: 8, Parity: none, Stop bits: 1, Flow control: hardware———————————————————-

    There is an excerpt from conversarion with Peter Ohler:
    I haven’t updated that code in a long time. I’ve included the source
    code for the application so you are welcome to download it and make
    what ever changes you like. Changing to 6 volts should be relatively
    easy and the Peukert’s equation should work find for any voltage.

    Any circuit you put together that make use of a serial interface
    should be fine once you modify the source code. The only input you
    need are voltage and current. You will also need time but that can
    come from the Palm or handheld device.
  9. Jerry Halstead    Jan 17, 2006 08:01 AM    #
    Thanks again Mesuge. I’ve taken the liberty of turning the URLs you posted into click-able links.
  10. — Richard    Mar 09, 2006 01:07 AM    #

    You can get Link 10s with the serial port. When you call Xantrex support, ask about this. They also sometimes have factory refurbished Link 10s for sale.

  11. darin    Jan 03, 2007 18:29 PM    #

    Here’s a basic metering question: how do I know what scale to get for an ammeter?

    Do I just match it to the max current of the controller? If so, what if you’re running a contactor controller or controller bypass?

  12. — James    Jan 03, 2007 20:00 PM    #

    I think batteries have a max current output based on their internal resistance. Maybe the battery specs will give s short-out current. I reckon, for example that when I fit my bypass, i won’t exceed 500A with my motor and Trojans. what makes me think this is that it’s actually only a small part of the rev range where I can get the controller’s max output (about 325A) most of the rev range only pulls obout 200A at full throttle. so I think the controller is not limiting the current by much. Also, and here’s the clincher – I have a 500A fuse! I have ordered my bypass contactor so I’ll be able to tell you by feb / march time what happens to the current for me. Meanwhile, you could do worse than reading EV dragster pages like John Wayland’s as to how they get their high currents and what limits them.

  13. darin    Jan 04, 2007 00:21 AM    #

    Thanks James. Leads me to the next question (with preamble).

    Preamble: regardless of what my actual max current limit may be, I’d really prefer to have a gauge with a small scale because it has better ‘resolution’ for taking accurate readings at a glance. (Also, hopefully, most of the time, we’re pulling low amps, right?)

    Question: what happens if I pick say a 200A ammeter, and occasionally draw much more than that (eg. full accel)? Do I have to buy another one each time? :)

  14. — James May    Jan 04, 2007 08:40 AM    #

    I don’t think a mechanical meter will be damaged by a bit of over-deflection. It may eventually go out of calibration if the overdeflection is too much. Mine overdeflects backwards by up to 50A when I am regenerating.
    The actual currents in the meter and the forces involved in deflecting it are low. so the danger is probably bending the needle and that seems unlikely. Anyone feel free to tell me I’m wrong here!

    My meter is 0-450A and I think that is a good sort of scale for my voltage (96V) if you ar erunning a higher voltage you might need smaler scale.

    You could also get round the ammeter problem by using the small scale ammeter for the controller and allowing the bypass to bypass the ammeter shunt. It will then read approx 0A when you are bypassed. you might like another small ammeter for the bypass current however, or you won’t know!

  15. darin    Jan 04, 2007 23:26 PM    #

    James, have you talked about your controller bypass here yet? I’d sure be interested to know how you’re going about it.

  16. — James May    Jan 05, 2007 09:30 AM    #

    I have a new wiring diagram for the Zapi which my EV supplier sent to me which includes a bypass controller.

    The Zapi contrller has a specific pin out for the bypass contactor so It decides when to apply the bypass. This is good because it means I don’t have to put an extra switch at the end of throttle travel which I would otherwise have to do. (Maybe I am mistaken on this point). I can email you the diagram, but it may only apply ot the Zapi. Essentially the bypass controller shorts out the PWM switching so that the series motor end up connected directly to the battery.

    I’m told the Zapi controller is very fussy and I guess it probably throw an error if you tried to bypass it manually.

  17. darin    Jan 05, 2007 09:46 AM    #

    The old GE EV-1 controller that came with the forklift also has a bypass circuit. But we will likely start by trying out a small Curtis first.

    If the Curtis will move the car adequately, adding a bypass to it would be an idea. I thought you might be doing a similar “home brew” upgrade, so the OEM schematic won’t apply here, but thanks anyway.

  18. — Nick Smith    Apr 02, 2007 22:53 PM    #

    After waiting 10 weeks! for Electric Transport to quote shipping of a Link10 emeter I discovered a local supplier of Xantrex equipment. The latest gage is called the XBM (Xantrex Battery Monitor I suppose). Judging from the tech spiel it looks pretty sophisticated but only works for the pack as a whole. There is an RJ12 connector on the back for hooking up the optional software interface with isolated RS232 port. The software looks interesting but I can’t afford that at the moment…

    I emailed tech support about ‘remoting’ the buttons of the link 10 so that I could mount it in the sealed intrument cluster. They suggested simply soldering momentary push switches in parallel with the ones on the circuit board – I suppose that could also be done with the new XBM too.

  19. — James May    Apr 03, 2007 08:25 AM    #

    Hi Nick

    -Soldering parallel momentary switches – it might void the guarantee! I have the old round link 10 emeter. Its a really good bit of kit, calculates the remaining percentage based on how hard you use the batteries (involves Peukerts exponent) as well as what energy you have used from them. This compensates for energy lost in the batteries at high drain rates.

    On a slightly different subject, I fitted the controller bypass and invited my EV supplier Robert to come and set it up. It’s funny. I found the controller was turned right down ( level 4/9) and that’s why it was not performing well. The controller is working really well now, giving me good low revs acceleration but it never seems to actuate the bypass controller which I spent 100 pounds (GBP) on. Oh well! My verdict, if you have a Zapi H2 don’t bother with the bypass, just turn it up to the maximum setting if you want the the power.

  20. — Nick Smith    Apr 03, 2007 20:11 PM    #

    You are right about the guarantee but sometimes ya just gotta do these things. I have a friendly electronics tech who could to do it for me but I can’t even figure out how to open the XBM anyway (without a knife at least)! If I can’t remote the buttons to mount it in the enclosed instrument console I will just have to mount it on the dash. I will likely move the radio lower down the console and use the free slot for the XBM and maybe some other indicators etc.

    As far as I can tell from a good reading of the manual the XBM is pretty much the same as the link 10 except for the fact that it takes all of its power from the traction pack (with optional prescaler of course). There are only 3 wires for the voltage sense and 2 wires for current. The price wasn’t too painful either.

  21. — Nick Smith    Aug 05, 2007 20:23 PM    #

    I am just about to wire in the current sense wires to the shunt and need a query answering. I was contemplating using CAT 5e network cable (4 twisted pairs) but the wires are very small. I thought maybe a good idea would be to wire 4 wires together (1 from each pair) and then connect the other 4 wires together. This gives 4 parallel twisted pair connections and the wires are now big enough to connect to a ring crimp terminal. Does anyone see an issue with this?

  22. — James May    Aug 06, 2007 07:22 AM    #

    I think it’ll be OK if the wire isn’t too long and if the impedance of your ammeter is nice and high.

    I used (an still using) CAT5 to measure voltages. Quite long lengths of wire (3-4m) and I was only using the single strands. When I used a low impedance voltmeter (my bargraph in “bar” mode rather than “dot” mode) then it drew lots of current (around 100mA) and there was a slight voltage drop over the CAT5. If you do what you are suggesting, you would proabably avoid the voltage drop and everything will be fine. Anyone disagree?

  23. — Nick Smith    Oct 25, 2007 17:24 PM    #

    Well – I just blew up a voltage prescaler!!! On reading the manual it does say that it will be destroyed if you reverse the polarity – and they mean it. A chunk flew across the garage!

    Anyway, how have others connected the link10 meter? I have a small DC/DC isolator for the 12v supply and obviously a new prescaler but there is only one -ve connection for both the 12v and voltage sense connections. The manual also shows the 2 -ve’s on the same terminal – is this correct?

  24. — James May    Oct 27, 2007 10:22 AM    #

    Hi Nick

    I will go out and check my e-meter wiring for you soon.

  25. — James May    Oct 27, 2007 14:15 PM    #

    I have 2 -ve wires on the same terminal. It’s the end terminal. It’s on the left if you look at the back of the e-meter. There are no other terminals with 2 wires. I also have a prescaler.

    Hope this helps.

  26. jerry Halstead    Oct 27, 2007 19:52 PM    #

    Hi Nick,

    Here’s the schematic of the emeter wiring on the Mazda.