Wanted - an amp hour meter

How do you store and manage your electricity?
User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

I don't want volts either Image I was just saying if you did want to incorporate volts into this unit, it would be troublesome, so probably best not to.

I can only run a voltmeter if I have a 1:100 or more divider inside the pack. I've ordered some big 14 W, 47k and 330R resistors for the job. Justin suggested I make a 0-5 V signal for volts and he can set the Vsense to read to within a volt or two.
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

You do realise that a divider attached directly to the battery still doesn't provide isolation, don't you? If you are powering the voltmeter from 12 V, it means the -ve battery terminal is now commoned up with the 12 V system -ve.

A can opener has got to be better than the bicycle!!

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

Sure it's not isolated, but it's a damn shade safer than having 700 V behind the instrument panel. I won't be grounding the low voltage system to the chassis, just running extra wire everywhere.

I rank the ideal invention as the most elegant, part simple, unbeatable creation which cannot be improved upon. The pedal powered bike fits the bill Image
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

I'm not sure I agree, because the -ve of the 12 V system is connected to the frame/chassis - otherwise you'd have to run 2 wires to everything! - and by using a voltage divider you connect the -ve of the high voltage battery to the chassis as well. This means that if you were to inadvertently touch a terminal of that battery anywhere above about the 70 V mark, you risk a lethal shock.

By the way, this is also my reason for choosing the Tamura sensor over a shunt.

Anyway, I'm not going to include a voltage reading in my simple meter. The prototype of which is complete and working quite nicely with a pot to simulate the Tamura sensor output. It even seems to be accurate!
I still have to do a new pcb layout and I've found some very much cheaper lcd's (down to about $5) so if you build one yourself you can do it for under $50.

Here's a test for the best invention:
You're stranded in the desert, all alone with a single can of water. If you can't drink, you'll die in less than a day. There's an oasis just over a day away. Given the choice of a bicycle or a can opener, which should you choose that might save your life?   Image
Last edited by Nevilleh on Sun, 27 Jan 2013, 01:27, edited 1 time in total.

Greg partridge
Groupie
Posts: 187
Joined: Sun, 01 Apr 2012, 16:19
Real Name: Greg partridge
Location: Dural
Contact:

Wanted - an amp hour meter

Post by Greg partridge »

Bicycle, but travel away from the oasis.

Shirker
Groupie
Posts: 40
Joined: Tue, 27 Nov 2012, 06:47
Real Name: Matt Smith
Location: Perth

Wanted - an amp hour meter

Post by Shirker »


Renard
Groupie
Posts: 219
Joined: Sun, 29 Aug 2010, 18:55
Real Name: Robert Fox
Location: Cobargo NSW

Wanted - an amp hour meter

Post by Renard »

Nevilleh wrote: I'm not sure I agree, because the -ve of the 12 V system is connected to the frame/chassis - otherwise you'd have to run 2 wires to everything! - and by using a voltage divider you connect the -ve of the high voltage battery to the chassis as well. This means that if you were to inadvertently touch a terminal of that battery anywhere above about the 70 V mark, you risk a lethal shock.


One of the advantages of using Neville's BMS and some others, is that it reports total voltage without the problems of having to isolate the output of a voltage divider which requires a linear optocoupler (such as the HCNR200) and associated circuitry.
I had been worrying about this problem of bringing un-isolated wires -- even at 30V or so -- into the cabin until I decided to use the BMS.
Renard

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Shirker wrote: This is a nice AH meter: http://www.lightobject.com/Programmable ... -P278.aspx


I beg to differ, its not nice at all! Crappy, 7 segment led display and uses a shunt with no isolation. A shunt is NOT the way to go - for the reasons I have mentioned before.

As Renard said, my bms reports the total traction battery voltage so all I want is accurate amps and amp-hours. I have built this meter as a stand alone thing to figure out how to do it, but I really want to incorporate it into the bms itself. I might even go to a four line display to show everything at once, but that is for the future.

Shirker
Groupie
Posts: 40
Joined: Tue, 27 Nov 2012, 06:47
Real Name: Matt Smith
Location: Perth

Wanted - an amp hour meter

Post by Shirker »

Shunt resistor: absolutely - apologies, I was asleep at the wheel...
LED display: I suspect Chris may prefer an LED on race day, but could be wrong on that too...

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

Why would the voltage divider be connected to chassis? Is there something inside the cycle analyst / panel meter which causes the two to be common?

The voltage divider from the traction pack will be isolated in the same way the main power leads are isolated - floating. So far in all of my schematics, nothing is to be attached to the chassis. Sure the ammeter 75 mV sense wires and divider negative are connected to the HV negative, but the HV positive is separated from the rest by a large resistor. Oh, and I'm well aware of the benefits of a Hall effect sensor over a shunt - it's just that I needed the extra attachments points for the precharge circuit, so it killed two birds with one stone. I wouldn't need to use it if the sensor did the same job.

LED/LCD display is attractive to keep it simple but if your display does Ah and A on the one screen, that's pretty cool too.

Oh, bicycle for the win. You can get to the oasis far more efficiently than walking with a can of water in your hand.
Last edited by jonescg on Sun, 27 Jan 2013, 06:47, edited 1 time in total.
AEVA National Secretary, WA branch chair.

Renard
Groupie
Posts: 219
Joined: Sun, 29 Aug 2010, 18:55
Real Name: Robert Fox
Location: Cobargo NSW

Wanted - an amp hour meter

Post by Renard »

jonescg wrote:   Sure the ammeter 75 mV sense wires and divider negative are connected to the HV negative, but the HV positive is separated from the rest by a large resistor.


Remember that ordinary resistors are not rated for high voltage. And one would have two or preferably more high value resistors each connected to the pos. and neg. Then, too, it's just possible the reduced voltage may need an op amp follower to prevent distorted readings, depending on the sensitivity of the meter.
Renard

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Well, you need to power the electronics from somewhere. You have two choices: 12 V or traction battery! If you are going to use a shunt resistor for current measuring, you could solve the isolation problem by powering the electronics from the high voltage. Your problem then is reducing it down to the 5 V most circuitry needs. If you have a 150 V battery and your meter draws 10 mA or so, then you'll need a 3 watt resistor or bigger to dissipate the 1 1/2 watts you are losing. Can be done, of course, but not very elegant. And a lcd backlight can draw 50 mA or more, so the power dissipation becomes a problem.
Also, the designer has to cope with a range of input voltages that may go from 48 V to 650 V which is not easy.
Last edited by Nevilleh on Sun, 27 Jan 2013, 07:32, edited 1 time in total.

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

I was planning on running a separate 12 V auxiliary battery for all of the 12 V stuff. Charge the night before sort of thing. I won't be running any electronics from the HV system. No, at these high potentials, DCDC converters get mighty impractical.
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Well, the A-Hr meter is done. If anyone would like to build one, drop me a PM with your email address and I'll send you the files, PCB Schematic and source code.
Here's a component list:

PL1     1       2 way header
PL2     1       5 way header
Pl3     1       3 way header
PL4     1     16 Way header socket     
C's     4     Capacitor     .1 uF
Electro 1       10 uF 25V electrolytic
U2     1     LM78L05ACM     
U3     1     OPA342UAG4     
U1     1     PIC16F1826-I/SO     
VR1     1     Preset (PCB)     100
R2     1     R 0.25W SMTF 10     2K2
R3     1     R 0.25W SMTF 10     10K
R1     1     R 0.25W SMTF 10     22K
R5     1     R 0.25W SMTF 10     270
R4     1     R 0.25W SMTF 10     270
R6     1     R-SM     10
R11     1     R-SM     10K
R12     1     R-SM     10K
R8     1     R-SM     26K1
R7     1     R-SM     26K1
R9     1     R-SM     510
R10     1     R-SM     510
SW1     1     SW_FSM2JH
LCD     1       16 x 2 line, backlit
Hdr     1       16 pin header for lcd
CS      1       Tamura L01Z400S05 Hall effect current sensor.
PCB     1       Printed circuit board
Plastic box to put it in - Jaycar?

As always, its all smd stuff with a double-sided board.

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

Nevilleh wrote:
As always, its all smd stuff with a double-sided board.


If I pay you more, will you mount and bake everything for me? I have zero experience with SM stuff Image
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

jonescg wrote:
If I pay you more, will you mount and bake everything for me? I have zero experience with SM stuff Image


Ah, you mean will I make one for you and sell it to you? Of course I will. How much money have you got? Image

A rough and ready costing says the parts cost $A44 and it would take me an hour to build one, for which I'd charge $55 for a total of $99. Plus postage and you have to put it in a plastic case yourself.
Last edited by Nevilleh on Mon, 28 Jan 2013, 10:02, edited 1 time in total.

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

You name a fair price and I won't argue ;) It doesn't need to be mounted in a box as I should be able to make my own dash.

Thanks Neville!
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Oh, I was editing my last post when your new one arrived. Look back - hopefully not in anger!

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

Nevilleh wrote: Oh, I was editing my last post when your new one arrived. Look back - hopefully not in anger!



Image

PM about to be sent :)
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

I've decided to make 10 of these as that is the minimum number of pcbs that I can get from ITEAD, so if anyone else wants to buy a complete unit they will be available in about 10 days. Or the pcb only. Just send me PM with your details.
Last edited by Nevilleh on Tue, 29 Jan 2013, 06:38, edited 1 time in total.

User avatar
PlanB
Senior Member
Posts: 465
Joined: Sat, 16 Jan 2010, 15:24
Real Name: Kris McLean
Location: Freemans reach
Contact:

Wanted - an amp hour meter

Post by PlanB »

Nevilleh wrote: Any ideas for other useful features? There is still 70% of the ROM available!


The CA has a 5v 9600 baud serial out which is nice for datalogging/telemetry
Image

Shirker
Groupie
Posts: 40
Joined: Tue, 27 Nov 2012, 06:47
Real Name: Matt Smith
Location: Perth

Wanted - an amp hour meter

Post by Shirker »

The JLD404 includes 2 relays that can be set to latch/unlatch upon measurement of two different thresholds of your choice of V, A, or Ah...

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Thanks, both good ideas.
I thought also to include two other outputs: a pwm signal that could drive the car's fuel gauge and show full to empty. That would require the battery capacity to be programmed in, of course. Probably only for Li cells as I couldn't be bothered with Pb-A and all that Peukert nonsense. And a variable frequency pulse train that could drive the tachometer so that it shows amps. ie what was 5000 rpm would be 500 amps.
Anyway, all those things are on the "to do" list for when I get bored.

Here's a new photo:

Image

Just to give an idea of the size, the viewing area of the display is 66 x 16 mm.
Last edited by Nevilleh on Wed, 30 Jan 2013, 04:46, edited 1 time in total.

User avatar
jonescg
Senior Member
Posts: 3108
Joined: Thu, 21 Jan 2010, 23:05
Real Name: Chris Jones
Location: Perth, WA.

Wanted - an amp hour meter

Post by jonescg »

That's a huge battery you got there Neville Image
AEVA National Secretary, WA branch chair.

Nevilleh
Senior Member
Posts: 773
Joined: Thu, 15 Jan 2009, 18:09
Real Name: Neville Harlick
Location: Tauranga NZ

Wanted - an amp hour meter

Post by Nevilleh »

Trying for maximum range!
The meter will go to 65535 AHrs - that's because its a 16 bit variable else you'd be stuck with a max of 255.

It checked out very well. I set it for 100 A and timed it while it counted up to 100 AHr and the error was too small to see on my stopwatch.
The main source of error will be the current sensor and that's supposed to be +- 1% or so.

Post Reply