ammeter accuracy - LEAF charging

I have an EVSE upgrade EVSE and I'm told that when it's programmed to output a certain current, it does exactly that.

The issue I'm running into is that I have two meters hooked up to a 240V circuit and the numbers just aren't matching.

I'm about 2-3A below what the EVSE thinks it's outputting.

I'm using two different meters:

1) Is FLUKE multimeter with a clamp-on ammeter
2) PZEM-004, (http://www.amazon.com/80-260V-BAYITE-PZEM-004-Multimeter-Voltmeter-Transformer/dp/B00YYA014W)

Both read in the same range (on either leg of the 240V circuit) but they are both consistently 2-3A below what the EVSE thinks is going out.

I tried changing the programming of the EVSE (the the leaf being at the same SOC) and it still is off. 16A programmed gets about 14.XX, 22A programmed gets about 19.5A, etc.

And I tested with the SOC at around 23%.

Here's the values of my test (all readings in amps)

PROG BAYITE D-BAYITE FLUKE D-FLUKE
10 9.05 -10% 8.02 -25%
14 12.27 -14% 11.16 -25%
16 14.22 -13% 13.1 -22%
22 19.53 -13% 18.48 -19%
24 21.38 -12% 20.34 -18%
AVG---> -12% AVG---> -22%

So....questions:

* Can both my ammeters be off and by that much?
* What other things can be the cause of this?

Thoughts?

-Andrew

I've noticed a similar thing with my EVSEupgrade'd EVSE, but not to your extreme. I get about 1 amp less with my ammeters than what the EVSE thinks its putting out. That is set for 20a and my ammeter says 19, set for 15a and my clamp on ammeter reads 14a. I just chalked it up to the EVSEupgrade being a bit on the cautions side, not wanting someone to set their EVSE to the maximum and overloading things....which now that I know it, I'm OK with it. Kind of like most vehicles speedometer, they tend to overstate the speed for those who like to ride the line.

Oh my Juicebox EVSE is similar, about 1 amp less output than it's set for

The EVSE doesn't output a current. The EVSE tells the car how much current to draw and then connects the car to the power mains with a relay (mechanical switch).

The car may or may not be accurate in consuming the requested current. If I were designing a car, I would consume slightly less than requested, to give some margin of safety. Perhaps that's what you're seeing.

Bob

^^^ that would make sense then as to why all 4 of my EVSE's(yes I know ) output basically 1a less than set for for, it's the car thats on the cautious side.
Again I'm OK with this as personally I like to push the envelope and this will help give me a little buffer since in my mind what I have it set for is what I consider it puts out

Yes, the EVSE just informs the car the MAX that it can draw. It's up to the car's on-board charger to do the rest. We've conducted lab tests with many EV's and we find that most will draw within an amp of the pilot providing the car's charge state and charger capability allows for it.

During balance operations, or in very high or low temps, you will often see the amps taper, which is normal.

I think this is making more sense now.

I'm about 99% sure that the fluke meter with the radio schlock clamp is just giving a hokey reading. I grabbed another clamp-on ammeter and will do some more readings tonight.

Furthermore, this is starting to make more sense that the leaf via the EVSE is actually throttling down the draw. No matter what my setting is on the EVSE, the car seems to drop it's "request" by about 13%. Since I can adjust the EVSE to output at any current, I can just choose what I want based on what I expect the leaf will do (and the proper upper limit of my 30A circuit (24A

-Andrew

I have two clamp on meters. One is peak and the other RMS. The RMS one agrees with my Mercedes B Class EV at 40A. The peak one reads slightly less.

As ingineer says the EVSE outputs a1Khz square wave that in the OpenEVSE case is accurate. The duty cycle sets the maximum current. At 30A it is symmetrical, Chris Howell's website has info on the J1772 protocol. It is strictly up to the car charger to implement the charging current assuming enough current is available.

I have a simulator that also measures the pilot. The OpenEVSE square wave is right on but the frequency is 1002 HZ. The stock Mercedes EVSE shows 1000Hz with 8A and 12A. I do not know what the frequency tolerance is but the OpenEVSE boards work fine.

Followup -

Grabbed a fluke clamp-on RMS meter from work that had just been calibrated and it reads dead-on (to the 100ths) what my PZEM-004 meter is reading. Tells me a couple of things:

1) That the cheapo PZEM-004 is pretty darn accurate
2) That the car is most certainly "throttling" down the the draw from the EVSE
3) That I can compensate for this by just changing the setting on the EVSEupgrade cable (as long as I'm still below the circuit parameters)

Cheers,
Andrew

You can certainly upgrade your EVSE settings. For 30A 32A DOES NOT EXCEED THE nec REQUIREMENTS. In general if for example the EVSE says 30A is available then the Leaf will only draw its 27.5A since 30A is plenty. The EVSE spec goes to 80A but the car charger will only take what it needs and ignore the rest.

I have read posts where a person has purchased a 40A juicebox and they are convinced the Leaf charges faster, WRONG! The car charger sets the current as long as there is enough. As long as over 27.5A is available then that's all you need. anything more is ignored and unless you are future proofing your EVSE then the money is wasted,