# what fuel guage do you use for your batteries?



## mxmtech (Apr 21, 2009)

The Kill-A-Watt measures AC current and gives you a reading of how much power you put into your batteries, is it possible to build a device which will measure the amperage, voltage of the battery output and automatically calculate how many ah I have used so that I can stop and recharge BEFORE I reach the dreaded 50% drain on my batteries?
Has anybody done this?
What about temperature change?


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## Jimdear2 (Oct 12, 2008)

mxmtech said:


> The Kill-A-Watt measures AC current and gives you a reading of how much power you put into your batteries, is it possible to build a device which will measure the amperage, voltage of the battery output and automatically calculate how many ah I have used so that I can stop and recharge BEFORE I reach the dreaded 50% drain on my batteries?
> Has anybody done this?
> What about temperature change?


I just looked this up for someone else (go figure) 

Google Cycle Analyst.

It is supposed to be a good one. They have a model good up to 200 volts.


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## dimitri (May 16, 2008)

Just measuring energy input and output is not good enough for LA batteries to determine SOC, because it will not account for Puekert effect.

You lose almost half of your stored energy due to Puekert because of high discharge rate.

Granted that SOC meters try to account for that, but I am sure that some of them may do better job than others.

I personally use PakTrakr, which has no current measurement at all, only voltage, and it seems to be pretty decent at SOC "guesstimation".

PakTrakr has an optional current sensor, but it has no effect on SOC calculations, or so I am told. With current sensor you would know how much energy went from battery to the motor, but it doesn't tell you SOC because of Puekert losses which happen inside of battery itself and cannot be easily measured.


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## ZeroGasoline (Jul 30, 2008)

Jimdear2 said:


> I just looked this up for someone else (go figure)
> 
> Google Cycle Analyst.
> 
> It is supposed to be a good one. They have a model good up to 200 volts.


You can find the cycle analyst at this link. Looks like the 200v edition is $150.

Personally I don't use anything special to monitor my LA battery pack (just the regular tools like a voltmeter and odometer). As mentioned before, without measuring the specific gravity of the battery itself, it's mostly guesswork. Even with measuring the specific gravity of the battery, I think it would be difficult to convert that information into a useful "fuel gauge" giving you estimated range remaining - there are a lot of factors that go into range calculation like the terrain for the rest of your trip and your driving style (which both boil down to the peukert's effect).

To me, it seems like you could spend a lot of money and end up with a guesstimate no better than what one could formulate themselves. (I will probably feel differently when I get a better quality battery pack though!  ).


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## Jimdear2 (Oct 12, 2008)

dimitri said:


> Just measuring energy input and output is not good enough for LA batteries to determine SOC, because it will not account for Puekert effect.
> 
> You lose almost half of your stored energy due to Puekert because of high discharge rate.
> 
> ...


dimitri,

It does seem that whichever aftermarket meter you look at, it doesn't do something you want it to do, measure, calculate or diaplay.

I read reviews on this one and it seems to do what mxmtech was asking about. He still has to make the choice.

Personally after reading about the advantage and dis advantage of a number of these meters and doing a cost analysis for using them in MY UNIQUE circumstance, I cant see the value.

I am going to fall back on the standard volt/amp meters and a pad of paper with pencil.

Bummer about tha redesign of the BMF 750 board. I'm waiting too, because I know that in the end my initial cautious start with 72 volts and 450 amps is not going to be enough. I like the size and what they are doing with the ability to access information through the data port.

You ought to look for a used useable size controler and put it in until the BMF is done, then sell the used controller when the BMF comes in. Get some use out of that investment.

Have a good day,


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## dimitri (May 16, 2008)

In my opinion the key difference in various SOC meters and BMS monitors is whether they only see overall pack voltage or individual battery voltage.

Unless SOC meter can see each battery individually, its not worth more than a plain analog voltmeter, IMHO.

The best part of PakTrakr for example is not its SOC gauge, its the fact that you have each individual battery performance at your fingertips, just pressing a button, instead of going around your pack with voltmeter, after paying $150 for useless SOC gauge.

From my experience and reading countless posts here, most pack troubles start with one weak battery, so if you can't spot that battery ASAP, you are in the dark.

I didn't bother with SOC on my first EV at first, didn't want to spend $200, thinking my voltmeter was good enough. After my first battery died, albeit it was replaced for free under warranty, I bought Paktrakr and absolutely loved it ever since.

I have PakTrakr on my 2nd EV now, with LiFePo4 cells, and its been a wealth of information, telling me how each cell behaves during charge and discharge.

I don't have anything against other SOC meters, I just don't see why people spend $150 on Cycle Analyst, when they can get PakTrakr for $200+


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## ZeroGasoline (Jul 30, 2008)

dimitri said:


> In my opinion the key difference in various SOC meters and BMS monitors is whether they only see overall pack voltage or individual battery voltage.


I think this is a very good point. I only have 6 batteries in my pack so going to each of them to check voltage isn't much of an issue. With larger packs, a monitor that could read all batteries in the pack (individually) would save quite a bit of hassle.

Also, if you were running anything other than lead acid, I think a battery monitoring system of some sort is absolutely necessary.


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## micheljaw (May 1, 2009)

A *fuel gauge* (or *gas gauge*) is an instrument used to indicate the level of fuel contained in a tank. Commonly used in cars, these may also be used for any tank including underground storage tanks.
-------------------------------------


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## Jimdear2 (Oct 12, 2008)

micheljaw said:


> A *fuel gauge* (or *gas gauge*) is an instrument used to indicate the level of fuel contained in a tank. Commonly used in cars, these may also be used for any tank including underground storage tanks.
> -------------------------------------


micheljaw,

If you are infering that the term fuel gauge is being used incorectly when applied to an Electric Vehicle, then think about this.

A battery pack can be considered to be a tank containing stored energy (watt hours) with its own fuel pump (voltage) because that is what it really is. 

Electrical fuel = watt hours

Then how is a Gauge that measures Watt Hours or Amp Hours (Fuel) in and out of the tank (batteries) not a Fuel Gauge.

If that was not what you meant. What was the purpose of the list of auto parts stores? Please be clear.


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## ZeroGasoline (Jul 30, 2008)

I agree jimdeer.

I've had people try to correct me when I say that I need to get a fuel gauge installed. They always say "don't you mean a battery meter?". It's a bit frustrating.

The fuel of an electric car is electricity, just like the fuel for an ICE is gasoline.

The fuel gauge for an ICE car displays the amount of fuel remaining that can be used by the vehicle.

Take the above statement, replace _ICE car_ with _electric car_, and the statement is no less true.


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## Jimdear2 (Oct 12, 2008)

ZeroGasoline said:


> I agree jimdeer.
> 
> I've had people try to correct me when I say that I need to get a fuel gauge installed. They always say "don't you mean a battery meter?". It's a bit frustrating.
> 
> ...


ZeroGasoline,

Bugs the h**l out of me as well. 

*EDIT See a following post by dimrti about BOTs (*&^&%$**#@! parasites) end edit.* By the way, *the BOT ------>*micheljaw, sorry if I came back a little strong

I'll take either fuel gauge or battery capacity gauge as interchangeable terms on an EV. 

All of the other names people generate are just confusing.

A battery is just a tank that stores chemical energy. The tank just gets refilled differently.


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## notnull (Jul 30, 2008)

+1 on the Cycle Analyst, I use it in my car.

http://www.diyelectriccar.com/forum...od-cheap-ways-measure-kwhr-29630.html?t=29630

Check out my reply to the above thread, I believe it is number 11 in the thread. 

Steve


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## dimitri (May 16, 2008)

Jim,

just wanted to let you know that micheljaw is not a person, its a bot, designed to infiltrate forums based on key words and post cleverly designed messages with advertizment links.

I bet you fell pretty silly knowing that you tried to reason with a machine 

I have seen a few of these bots on this forum, admins should really improve their signup code to better distinguish humans from bots 

Isn't it amazing that we live in the age when you talk to a machine without realizing it?

Now, where is John Conner when you need him?


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## Jimdear2 (Oct 12, 2008)

dimitri said:


> Jim,
> 
> just wanted to let you know that micheljaw is not a person, its a bot, designed to infiltrate forums based on key words and post cleverly designed messages with advertizment links.
> 
> ...


Naw I don't feel silly, just sad that there are people who inflict this kind of crap on people who just want to do their job and live clean and simple.

These poor slobs think that they have accomplished something of value LOL.

People who do stuff like this are knowing parasites, just like politicians and about half of the "buisness managers" in this world. They do this stuff because they think this puts them above the rest of us. The old I put one over on you attitude.

We don't only need John Connors we really need John Gault.

I hope you are one of the lucky generation that got to find out who John Gault was, those before "modern politicaly coreect pollitically controlled so called teachers and unions took over the education system"

Enough vitrol, back to being my simple self doing my simple job.

Thanks for the heads up and have a great day.


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