calibrating a cycleanalyst with a watt meter?

RVD

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Hi,

Is there a way to calibrate a cycleanalyst with a turnigy watt meter?

I have a $25 turnigy watt meter (http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=10080) and also a cycleanalyst.

My setup is a lyen 12 fet sensored controller, crystalyte HS 3540 rear, 48v 20ah lifepo4. My rshunt value in the cycleanalyst is set to 2.4.

On my commute this morning, according to my CA, i used up 10.81ah, 565.98 watt hours, 33.0 wh/mile.

According to my turnigy watt meter, i used up 12.5ah, 630 watt hours.

distance is 16 miles and i usually ride WOT as much as i can (limited to 30amps).

Does this mean that I need to reduce the rshunt value on my CA? is the watt meter accurate?
 
I'm definitly no expert, but thats pretty much how I calibrated mine, there is a more precise way I've heard, but haven't tried.
I just kept going for rides and changing my rshunt value until it was the same as turnigy watt meter. also looked at the MAH on the icharger when charging it back up for reference. if I used 2AH on my ride, but the icharger needed 1.5AH to charge the pack up I knew it was still off.

good luck :D
 
thanks. the problem is that unlike lipo (which i can use for awhile to calibrate i suppose), i'm using lifepo4 for my commuting battery. this just means that i don't know how many ah i am putting back into the battery when i charge. the charger just plugs in and eventually turns green when done.

should my rshunt go down or up if my CA ah reading is lower than my turnigy watt meter ah reading?
 
I started off by first calibrating to the no-load amps. my motor uses about 4 amps no load according to the watt meter so I messed w/ the rshunt until my CA read 4 amps no-load.

then I went for a few rides and checked the values again...

RVD said:
should my rshunt go down or up if my CA ah reading is lower than my turnigy watt meter ah reading?

can't remember. just use trial and error. first make large changes in the rshunt value until you know how it works and then make smaller tweaks until it's "close enough"

I'm sure someone will post on here a better way to calibrate a CA (hint) :mrgreen:
 
thanks gensem, here's that info,

Of course, your controller needs to have a 6 pin CA connector for me to be able to perform this service.
Here is how I do it:


1) I plug the CA into your controller
2) I attach a power supply to your controller (typically 48V)
3) I set the iCharger constant current source (Foam Cut) to 20A
4) I attach the (+) iCharger output to your main ground
5) I attach the (-) iCharger output to one of your phase leads
6) I turn on the controller to power the CA
7) I activate the iCharger to drive the constant current
8) I note the value displayed on the CA
9) I turn off the current source

10) I calculate your new CA setting and program it
11) I then repeat the test to confirm settings are +/- 0.1A

This procedure works by driving a constant current through the main ground, through the shunt, through the body diode of the main fets, then out the phase lead. Credit for this procedure goes to Justin from ebikes.ca

-methods
 
10.81AH / 12.5AH = 0.8648 Multiply your CA shunt value by 0.8648 and you should be close to matching the Watt meter (and assuming it's calibrated correctly).


I calibrated both of my CA shunt values to my icharger 208B this way and when I charge the batteries at 0.25C rate (40AH all in parallel 6S8P) I'm within 100mA every time (at least I know the measurements are repeatable). If you are fast charging at 1C+ and using the meters reported amount put back in this method will not be as precise. Methods way is great too.
 
Just as zombiees said, calibrating just using the amp-hours (or watt hours) from an external pre-calibrated reference meter is the easiest way to go. The only limitation is that the CA will not be any more accurate than your reference meter is!

Here's the whole process:

1. Start with a charged battery.
2. Reset the amp-hour counter on your CA
3. Hook up a Watts Up or other watt-hour meter between your battery and your controller
4. Make sure you are not drawing a bunch of other current through the Wh meter which is NOT going through the controller shunt (the way my bikes were wired, I had to turn off my lights for this to work right)
5. Ride, ride like the wind! Use a few amp-hours from your pack.
6. Compare Amp-hours from your CA ("Ah_measured") to Amp-hours from your Wh meter ("Ah_actual")
7. Now calculate the new shunt value using the current CA shunt setting "S_old" and this formula:
S_new = S_old * Ah_measured / Ah_actual
8. Repeat steps 1-6 to confirm that your CA now shows the same Ah/Wh as your reference meter.

Example:

Let's say you program your CA for shunt value 4.000 MOhms, and then went for a ride. During that ride the CA measured 3.166 Ah while the trusted reference meter measured 2.716 Ah. You can calculate a more correct shunt value as 4.000 * 3.166 / 2.716 = 4.663 MOhms.
 
there is only one proper way, its simple just put the bike on a stand and run WOT with a DC amp probe clamped to one motor wire and set the CA RShunt value till the amps read the same as the amp probe. 0.001 +/- will be a large change on a larger motor. I guess you could use the brake to load it some as well. There is no way to get it spot on any other way. Then you will know your batteries gas tank size once you run it till cut out and will be able to see if the battery is falling off over time.

warning...Many amp probes will not read DC amps. I picked up one in Sears for $49 that will but maybe you can find cheaper.
 
Paul_G that's not a bad idea either. Using an external DC amp meter and tweaking the value up/down until the CA matches the meter is also a simple and direct way to do it. That would also be a good technique if you have one of those meters.

However, it's not the only proper way. Using a WattsUp meter does work very well, or any reference current/power/energy meter. In the absence of a reference meter you can also test the shunt resistance using a known reference current from your battery charger (as methods described), or as others have mentioned before, by looking at the amount of amp-hours your charger puts back into the battery after a ride (not as accurate due to charging losses but probably better than a guess or round number).

The $49 DC clamp meter (about the cheapest you can get) is not necessarily going to be any more accurate than the WattsUp, or other RC-style inline energy meter, or the CC output of your charger. My $350 Fluke 337 meter, when used as a DC amp clamp, is only accurate to about 0.2 amps..
 
one minor note. don't forget to adjust your readings in your CA if you have brake regen enabled.

e.g. if your CA reads 10.5ah used and you regenerated .8ah then you used a total of 11.3ah, not 10.5ah.
 
Yes, but only a net of 10.5 came out of the battery, therefore 10.5 should be used to calibrate.
 
Lyen 12fet MK2 controller Rshunt value for CA is 2mohm just for reference.
 
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