Total newbie looking for advice for DC voltmeter/ammeter

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zoghtegreat
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Posted by zoghtegreat: Thu. Nov 9, 2017 - 05:52 PM
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Hi everyone!

I'm a total newbie to Arduino and I'm starting my first Arduino project and I figured, meh, why make it easy? 

I'm building a electric mini chopper that will be powered be a 48v 12ah battery pack. My controller can draw up to 200 amps max and I want to make a "fuel gauge" that shows both volts and amps. 

Just to clarify, a fully charged 48v pack is actually around 57 -58 volts, so I want the voltmeter to read up to 60v. I would like the ammeter to read up to 200a if possible. I do understand that I will need a good quality shunt for something like this.

I've found a couple of post on different website on how to make individual voltmeters and ammeters, but I haven't found any that combine the two.

I'm planning to follow this tutorial to make the speedometer/tachometer:

http://www.instructables.com/id/...

So I would like to use the same display if possible.

I have "OK" coding skills in a couple of different languages, (I put the OK in parenthesis because my son is a developer for Openstack SDN and he laughs at my code! ;) ), so I'm not afraid to approach this project as a beginner.

Does anyone have any suggestions?

Thanks

zog

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Learning and Information, General Electronics
Last Edited: Thu. Nov 9, 2017 - 06:18 PM
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gchapman
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Posted by gchapman: Thu. Nov 9, 2017 - 08:47 PM
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current limit ... current limit ... current limit ... current limit ...

Current limiting by electronics is more reliable than by software.

Cells have safeties for a reason (open circuit before smoke before venting with flame before explosion)

 

fuel gauge - in IC form in several parts catalogs.

 

The laughter of ones who read your code - let that be water off your back.

Constructive review keeps you in the game.

Welcome!

 

"Dare to be naïve." - Buckminster Fuller

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Simonetta
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Posted by Simonetta: Thu. Nov 9, 2017 - 11:39 PM
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What is an "electric mini chopper" and what does it do with 200 amps at 48V?  Isn't that a lot of electric power?  Is it dangerous?
 

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tpappano
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Posted by tpappano: Fri. Nov 10, 2017 - 12:00 AM
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Weren't they using one toward the end of the movie "Fargo"?

 

Tom Pappano
Tulsa, Oklahoma

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Kartman
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Posted by Kartman: Fri. Nov 10, 2017 - 12:12 AM
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It’s not a motorbike baby, it’s a chopper!
Hopefully it’s not Zed’s, ‘cos we know what happened to him!

If you use a current sensor like a cs200a, that interfaces easily to an Arduino. Note you only have resolution of around a half an amp. Other suggestions might be a LEM hall effect sensor, but these are much more expensive but you wont need to cut the wire.
Measuring the voltage is two resistors. There’s a zillion examples on the web for measuring higher voltages with the arduino.
Basically the code consists of reading the Analog value, doing a little math and displaying it. Rinse and repeat.

Last Edited: Fri. Nov 10, 2017 - 12:18 AM
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gchapman
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Posted by gchapman: Fri. Nov 10, 2017 - 12:35 AM (Reply to #5)
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Pedal powered chopper though with a huge rear tire; the bike could use some electric assist to get one over rollers :

AtomicZombie Extreme Machines

AtomicZombieTM

The OverKill Phat Ass Extreme Chopper

http://www.atomiczombie.com/OverKill%20Phat%20Ass%20Extreme%20Chopper.aspx

AtomicZombie

 

"Dare to be naïve." - Buckminster Fuller

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DocJC
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Posted by DocJC: Fri. Nov 10, 2017 - 05:15 PM
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Welcome to the Forum.

 

I'd suggest approaching your project one step at a time.

 

First work on the voltmeter, alone, and display its data.

 

Then work on an ammeter, alone, and display its data.

Yes, a current shunt is the classic way to do this, but shunting 0 to 200 A, safely, and accurately, is a little bit more involved than it might first appear.

The suggestion above to use a clamp on ammeter type sensor is a great one, at least for the first version of the project.

 

Then, albeit with rather low resolution current data, build your battery gauge / energy meter.

 

Got all that working?

 

Then consider a higher resolution current sensor or current sensing technique to increase the "accuracy" of your battery gauge.

 

Note that if your circuit doesn't also measure the charging current INTO the battery, then I assume the battery charges up all night, and one hits a reset button to set the battery meter to "full" the next morning?

 

JC

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zoghtegreat
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Posted by zoghtegreat: Sat. Nov 11, 2017 - 02:58 AM
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gchapman wrote:

current limit ... current limit ... current limit ... current limit ...

Current limiting by electronics is more reliable than by software.

Cells have safeties for a reason (open circuit before smoke before venting with flame before explosion)

 

I'm not really trying to limit my current, just monitor it so that I know how much battery life I have left.

 

gchapman wrote:
The laughter of ones who read your code - let that be water off your back.

Constructive review keeps you in the game.

Welcome!

 

LOL, my son and I tease each other all the time. I'm better at mechanics, but when it comes to coding? WOW! Look out. What takes me 50 lines of code, he can parse down to about 5 or 10.

 

Simonetta wrote:

What is an "electric mini chopper" and what does it do with 200 amps at 48V?  Isn't that a lot of electric power?  Is it dangerous?
 

 

Essentially, it's a souped up electric scooter. I've been modding electric scooters for about 5 years now and it's a lot of fun, (for me wink ). Normally, you want to run your e-vehicle at the lowest amps possible to conserve battery life and extend the distance you can travel. However, the controller that I'm using can send up to 200a to the motor if you twist the throttle hard. And, well it's a chopper, your supposed to leave some of your back tire on the road from time to time! smiley 

 

Kartman wrote:

It’s not a motorbike baby, it’s a chopper!
Hopefully it’s not Zed’s, ‘cos we know what happened to him!

 

 

"Zed's dead, baby. Zed's dead".

 

Kartman wrote:
If you use a current sensor like a cs200a, that interfaces easily to an Arduino. Note you only have resolution of around a half an amp. Other suggestions might be a LEM hall effect sensor 

 

Like these?

 

https://www.ebay.com/itm/50A-100...

 

https://www.ebay.com/itm/ACS758L...

 

http://www.kr4.us/acs712-breakou...

 

https://www.ebay.com/itm/CR-Magn...

 

 

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zoghtegreat
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Posted by zoghtegreat: Sat. Nov 11, 2017 - 03:07 AM
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DocJC wrote:

 

I'd suggest approaching your project one step at a time.

 

First work on the voltmeter, alone, and display its data.

 

Then work on an ammeter, alone, and display its data.

 

 

This was the approach that I was planning to take, however, I don't know enough about Arduino's, (yet), to know where to start hardware wise. I have found a lot of examples of finished projects, but for some reason, people don't list the components that they use. Very frustrating.

 

DocJC wrote:

 

Note that if your circuit doesn't also measure the charging current INTO the battery, then I assume the battery charges up all night, and one hits a reset button to set the battery meter to "full" the next morning?

 

 

I'm actually looking to do something that show's battery and amp's in real time. When the scooter/chopper is powered down, the "gauges" will be off. When I turn the key, the gauges will come on, showing me how much battery life is left and when I start riding, the ammeter will show me how much I need to ease up on the throttle. wink

 

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Kartman
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Posted by Kartman: Sat. Nov 11, 2017 - 05:50 AM (Reply to #8)
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The first two are what I'm talking about. The second two are not suitable - #3 is too low current, #4 is AC only. The first one is probably your best choice - terminating wiring for 200A is plumbing, not electrical work so whatever makes it easier, is most likely the best choice.

 

This is the type of LEM product I'm referring to: https://www.digikey.com/product-...

'Tis quite a bit more expensive and a little more work to interface, but has the advantage you don't need to play around with terminating high current cables. I did come across some cheaper Chinese made devices when fixing an inverter welder. The fact that I had to fix the current sensor tends to suggest they aren't too good! The surface mount resistors were failing!

 

Also note depending on the type of battery, it might have trouble delivering 200A. If it is a fork lift battery or a car battery, no problems but a gel cell might not be so beefy.

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SHARANYADAS
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Posted by SHARANYADAS: Sat. Nov 11, 2017 - 09:11 AM
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I built voltmeter + ammeter for my power supply before!

 

use a voltage divider to scale the 60v to ADC's reference voltage range.Use external ADC (like MCP3202/12bit or  MCP3424/18bit) rather than internal 10 bit ADC to get a more precise reading!

 

For the Ammeter part,use ACS759 breakout board(Check this link to get an idea) to sense current rather than using shunt.

 

For say,if you use Internal ADC(which has a reference voltage of 5v say) then you have to use a 12:1 voltage divider to scale down the 60v to 5v range).If you use MCP3424(which has a reference voltage of 2.048v),then you have to use 28:1 voltage divider to scale down the 60v to 2.1v range.

 

you can feed the ACS759 output to MCP3424's another input(via a voltage divider accordingly) to measure the current.These ar hall effect based sensors!

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