# Battery power meter and amp counter



## cts_casemod (Aug 23, 2012)

Hi all,

I am looking for an amp counter/meter for my conversion. It would be nice if it had voltmeter as well but not really needed. I want something cheap to add to my battery packs, if possible with some kind of relay to shutdown the load once a preset capacity has been reached.

Sure you guys can point me into the right direction?


----------



## frodus (Apr 12, 2008)

JLD404

http://www.lightobject.com/Programmable-Digital-AH-meter-Ideal-for-battery-monitoring-P278.aspx

Also need a 75mV shunt (choose a shunt that would work with your full range of amps on the batteries, i.e. 500A)
http://www.lightobject.com/Shunt-and-AC-Coil-C27.aspx


----------



## Ziggythewiz (May 16, 2010)

Yup. $65, plus $10-15 for the shunt. Don't know what shipping would be to London, stateside it's $10.

Ammeter, AH counter, voltmeter. 2 triggered programmable relays.


----------



## Elithion (Oct 6, 2009)

E-Xpert Pro


----------



## cts_casemod (Aug 23, 2012)

Ziggythewiz said:


> Yup. $65, plus $10-15 for the shunt. Don't know what shipping would be to London, stateside it's $10.
> 
> Ammeter, AH counter, voltmeter. 2 triggered programmable relays.


I will be using a hall sensor for isolation, instead of the shunt.
It does seem just what I need. I am however a bit cautious when ordering from the USA. I always have about 30$ in cearance fees plus standard custom fees. Any retailer on europe?

I was wondering if this can read reverse current. Say the charge/regeneration amps?


----------



## Elithion (Oct 6, 2009)

cts_casemod said:


> Any retailer on europe?


The E-Xpert pro comes from Europe: The Netherlands.
tbs-electronics.nl


----------



## frodus (Apr 12, 2008)

cts_casemod said:


> I will be using a hall sensor for isolation, instead of the shunt.
> It does seem just what I need. I am however a bit cautious when ordering from the USA. I always have about 30$ in cearance fees plus standard custom fees. Any retailer on europe?
> 
> I was wondering if this can read reverse current. Say the charge/regeneration amps?


The JLD404 works only with a shunt, and needs to read right off the pack for voltage. It shares a common for the shunt.

Isolating would be difficult, so I'd say get something that is already isolated if that is your requirement.


----------



## Ziggythewiz (May 16, 2010)

cts_casemod said:


> I will be using a hall sensor for isolation, instead of the shunt.
> It does seem just what I need. I am however a bit cautious when ordering from the USA. I always have about 30$ in cearance fees plus standard custom fees. Any retailer on europe?
> 
> I was wondering if this can read reverse current. Say the charge/regeneration amps?


JLD404 only takes the shunt, I know there are a few AH counters around that use hall effect but don't know if any have relays built in.

Reading negative (charge) current is no problem.

When the European branch of the EVTV store opens I'm sure they'd be able to provide one for double the cost without the import fees


----------



## Elithion (Oct 6, 2009)

It's much easier to isolate the 12 V supply. That's what's done in the Sparrow. A 12V - 12 V DC-DC converter powers the E-Meter (a.k.a.: Link10), which is the equivalent to the E-Xpert.


----------



## cts_casemod (Aug 23, 2012)

Ziggythewiz said:


> JLD404 only takes the shunt, I know there are a few AH counters around that use hall effect but don't know if any have relays built in.
> 
> Reading negative (charge) current is no problem.
> 
> When the European branch of the EVTV store opens I'm sure they'd be able to provide one for double the cost without the import fees


The wonderfull EV market in Europe. Fees, laws, taxes...!

The method for current reading is irrelevant. 
If it is set up for 300Amps @ 75mV I only need to step down the 0-5V from my hall sensor to make it 0 to 75mV. In Fact i get better accuracy because the losses and noise at 5V are less than at 75mV. 

I have a standard Amp meter using a similar setup. A pot adjusts the voltage divider, since I have other stuff reading the hall sensor (brake light for regen, throttle, etc).


----------



## Ziggythewiz (May 16, 2010)

Oh...okay. I didn't realize it was in the same range. That's good.

Also, JLD404 is already isolated.


----------



## cts_casemod (Aug 23, 2012)

Ziggythewiz said:


> Oh...okay. I didn't realize it was in the same range. That's good.
> 
> Also, JLD404 is already isolated.


 
Yes, the hall sensors are linear. 
Shame the current transformers are not. There is a large variety of KW meters for AC. I think we pay a premium for having high voltage DC conversions. There are lots of things for bikes and such.



Elithion said:


> It's much easier to isolate the 12 V supply. That's what's done in the Sparrow. A 12V - 12 V DC-DC converter powers the E-Meter (a.k.a.: Link10), which is the equivalent to the E-Xpert.


 
Not quite.
The point in having an isolated system is to know that the main pack voltage is not traveling trought the car. Even with the DC-DC you still have the shunt wires comming from the pack. I just dont want to take any chances


----------



## Ziggythewiz (May 16, 2010)

I'm a DVMaholic so I have a mess of wires coming from the pack. All are fused at the source at 1/2 A or less so I'm not too worried about potential shorts.


----------



## cts_casemod (Aug 23, 2012)

Ziggythewiz said:


> I'm a DVMaholic so I have a mess of wires coming from the pack. All are fused at the source at 1/2 A or less so I'm not too worried about potential shorts.


Tell me about wires... All the signal wires from my controller to other devices are a nightmare  luckly they are mostly 12 and 15V 
I use a small resistor where required to read voltages from the pack.

I was speaking with a member on a different forum and he came up with this solution: http://forums.aeva.asn.au/forums/wanted-an-amp-hour-meter_topic3368_page2.html. Seems decent. Hes working on some code to drive the fuel gauge as well.


----------



## swoozle (Nov 13, 2011)

cts_casemod said:


> Tell me about wires... All the signal wires from my controller to other devices are a nightmare  luckly they are mostly 12 and 15V
> I use a small resistor where required to read voltages from the pack.
> 
> I was speaking with a member on a different forum and he came up with this solution: http://forums.aeva.asn.au/forums/wanted-an-amp-hour-meter_topic3368_page2.html. Seems decent. Hes working on some code to drive the fuel gauge as well.


Can you post the schematic and source?

Thx


----------



## DDDvvv (Apr 2, 2012)

I was checking out that Jld404, and then I learnt that it samples only 3 times per second. 

In todays microcontroller world, 3 samples/sec is like forever. Very low sample rate, means missing out on spikes, and peaks, and surges. Adc's are now averaging 250ks/sec. I bet ya that the routine driving that led is taking forever.

I would probably seek other options before settling on this particular item, but then again, as it was mentioned, the dc watt meter options are very slim.

Im wondering if those hundreds of ac watt meters can be hacked to measure dc......


----------



## cts_casemod (Aug 23, 2012)

DDDvvv said:


> I was checking out that Jld404, and then I learnt that it samples only 3 times per second.
> 
> In todays microcontroller world, 3 samples/sec is like forever. Very low sample rate, means missing out on spikes, and peaks, and surges. Adc's are now averaging 250ks/sec. I bet ya that the routine driving that led is taking forever.
> 
> ...


I find 3 samples per minute pretty accurate to be fair. In real world terms your car does not accelerate a lot in that period so if you look at such a small scale the difference in amps from 300ms to 600ms is quite unsignificant. I trust the error gained in a 75mV shunt is probably higher than that if you take the drain from the DC-DC and other drains that may only take a few mA from the pack during a long period of time. There is not much resolution in a micro at 0.075V so you are using only a few values the ADC is capable of.



swoozle said:


> Can you post the schematic and source?
> 
> Thx


I sent him a message asking for permission to post here. In the meanwhile you might want to check this one. I have been using it since 2005 on a power supply and recently on my e-bike battery. It doesnt save data after a power off, measure reverse currents or saves data, but you can make one for $15, just simply measures amps hours with a decent resolution:

http://elfly.pl/multimetr/multimetr_en_DIP.htm


----------



## Lopezjm2001 (Nov 22, 2011)

frodus said:


> JLD404
> 
> http://www.lightobject.com/Programmable-Digital-AH-meter-Ideal-for-battery-monitoring-P278.aspx
> 
> ...


Can someone verify that this AH meter can measure current in both directions. Some of these units only measure current in one direction only. Thanks.


----------



## Ziggythewiz (May 16, 2010)

Yes it does as long as what you're reading is in range. For example, as configured mine can only read to -200A.


----------



## dimitri (May 16, 2008)

We just reduced prices on EV Display to be more competitive with other products. 

http://minibms.mybigcommerce.com/products/EV-Display.html

$149 for round case unit or $129 for open square board.

There have been new features added to the firmware lately, such as remembering last SOC even if 12V power is turned off, optional config for Idle Current, which counts tiny idle current while the car is off for long time periods. This feature does not actually measure current since its too small to register, instead you configure estimated idle current, which you have to measure or calculate for your battery.


----------



## Lopezjm2001 (Nov 22, 2011)

Hi Dimitri,

How long can the network cable be between the display and the PCB for the EV display unit. I found that it would not work with a twenty metre network cable.


----------



## kennybobby (Aug 10, 2012)

One could use an isolation amplifier such as the AD210 to read a shunt on the high voltage pack and interface with the low voltage stuff...


----------



## dimitri (May 16, 2008)

Lopezjm2001 said:


> Hi Dimitri,
> 
> How long can the network cable be between the display and the PCB for the EV display unit. I found that it would not work with a twenty metre network cable.


20m is a pretty long cable, longest I tested with was 25ft (7.6m)

Is this installed in a stretch limo? 

Yes, there are limitations to cable length due to noise pickup and voltage drop, so I think your results are what to be expected.


----------



## Lopezjm2001 (Nov 22, 2011)

dimitri said:


> 20m is a pretty long cable, longest I tested with was 25ft (7.6m)
> Is this installed in a stretch limo?


No stretch Prius, it's for an off-grid solar power system which is located outside. I want the display unit inside the house so hence the long length.


----------

