# kWH monitoring system - anyone has build recipe?



## Stunt Driver (May 14, 2009)

I would like to keep track of energy use in car - kWH meter. Ideally - both charge and run.

All that is needed - proper microcontroller, that will multiply current by voltage and summ it up in small intervals - giving kWH number. Knowing battery pack capacity - this would be a perfect meter to tell how much is left. 
Also, by measuring charging capacity - would be easy to tell efficiency of battery pack. I have a feeling that my old LA troyans take 3 times more charge than what they are able to give back later.


So is there an easy recipe to use?


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## neanderthal (Jul 24, 2008)

I don't think there is an easy way to do this. I believe that some SOC meters actually measure this, but most just look at voltage and then estimate

I think that this one does it the "batman" 

http://www.cloudelectric.com/product_p/me-bm-ev-200.htm


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## Stunt Driver (May 14, 2009)

Nice unit indeed. Just a bit too exepnsinve for my project. Still many thanks for link - at least I know what exists.

SInce I have my volt and amp meters bought from ebay at very reasonable price - AH meter is the only part on wish-list. Will be looking for ways to assemble it

Just doesn't seem right: KillaWatt is $35 for all the same features. So DC meter doesn't have to cost $500 by nature of it.


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## Lordwacky (Jan 28, 2009)

Stunt Driver said:


> Nice unit indeed. Just a bit too exepnsinve for my project. Still many thanks for link - at least I know what exists.
> 
> SInce I have my volt and amp meters bought from ebay at very reasonable price - AH meter is the only part on wish-list. Will be looking for ways to assemble it
> 
> Just doesn't seem right: KillaWatt is $35 for all the same features. So DC meter doesn't have to cost $500 by nature of it.


an easy way to record the power you input into the car (including charging loses) is to buy a standard home electrical meter off ebay and wire it inbetween the outlet and charger. It will measure the kW-hr used during each charge cycle. You then divide by the miles traveled between each charge cycle to get a kW.hr/mile figure.

the best way to record energy output of the car is to do what you propose, gather the Battery voltage*current and time intervals and integrate over time. There are BMS systems out there that do this, I think the paktrakr can do it.


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## Stunt Driver (May 14, 2009)

So using KillA Watt at charging is easy, and gives some interesting info. Only costs $25,

But those BMS that you point to - cost well over $500, which is unreasonably expensive.

I am looking to have a simple kWH reading while driving. There must be microcontrollers that are able to do that, but i'm not familiar with that world. I bet total cost of such device could be $20 plus display


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## Lordwacky (Jan 28, 2009)

Stunt Driver said:


> So using KillA Watt at charging is easy, and gives some interesting info. Only costs $25,
> 
> But those BMS that you point to - cost well over $500, which is unreasonably expensive.
> 
> I am looking to have a simple AH reading while driving. There must be microcontrollers that are able to do that, but i'm not familiar with that world. I bet total cost of such device could be $20 plus display


Yes using a Killawatt is easy as long as you are charging at 110V and low current (15amps or lower). There have been cases where Killawatts have blown under the heavy use associated with an EV.

essentialy all the paktrakr is is a micro controller that does what you want with added BMS features, but it is a bit spendy.

Curtis has some SOC meters that might work for you. They tend to be for lower voltages though. I'm not sure what price you are willing to pay, nor do I know the voltage of your conversion. But you can see if any of these will work for you.

http://curtisinst.com/index.cfm?fuseaction=cDatasheets.dspListDS&CatID=25


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## Stunt Driver (May 14, 2009)

Thanks, interesting!
But SOC is really a volt meter, and as I see - doesn't monitor amount of electricity passed thru it. Am I looking for something too weired?


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## parscheese (Jun 21, 2008)

http://www.ebikes.ca/drainbrain.shtml


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## AmpEater (Mar 10, 2008)

parscheese said:


> http://www.ebikes.ca/drainbrain.shtml


I think the cycle analyst is exactly what you want, not very expensive either.

If that is too much it wouldn't be super hard to roll your own.

Something like an arduino or other cheap microcontroller, doing instantaneous voltage combined with a shunt and some basic math (maybe record average current over 10 second intervals?) should get you a reasonably accurate kwh reading. 

Compare with kill-a-watt and you'd have an excellent idea of kwh left, plus overall efficiency of your batteries.


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## Amberwolf (May 29, 2009)

I agree that the CA is the most informative option for the price--it's what I was going to suggest when I saw the thread title, but I was beaten to it. 

There are others around that do similar things, but they are not nearly as capable as the CA. I'd have one on my ebike if I had the money for it right now. (I still will if I can ever get out of this hole).
________
AlexxaDream


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## WSJ (Sep 18, 2008)

To log EV performance you will need the following equipment: AC kWh meter, wired to your EV charger and a Link-10 programmed to display kWh.

I use the following form to record the measurements and enter the data in to Excel to perform the calculations. If anyone would like a copy of my Excel form, send me an email at [email protected]. 

The graph shows the design performance analysis of my automatic battery charger controller. The design goal is to terminate the charge cycle after the 135% of the trip kWh has been reached. The automatic battery charger controller can be used on any charger without an internal controller.


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## Stunt Driver (May 14, 2009)

What is Link-10?
I realized I only need cumulative AH reading to do the math and to change my driving to be more efficient.

Found some xantech or so site, with 12-24 volt Link meter. But yours obviously much higher voltage?

I have Kill-a-watt AC meter, but main part missing is DC AH or KWH meter


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## WSJ (Sep 18, 2008)

Stunt Driver said:


> What is Link-10?
> I realized I only need cumulative AH reading to do the math and to change my driving to be more efficient.
> 
> Found some xantech or so site, with 12-24 volt Link meter. But yours obviously much higher voltage?
> ...


You will need a Xantrex Link 10 Prescaler 500V for Link 10

http://www.winstonsolar.org/info/parts.html


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