How to create reliable stable Current Drain

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How to create reliable stable Current Drain

Postby FioranoCars » Fri Jan 25, 2013 12:20 pm

Hi
For a number of tests we simulate load (current) on a circuit to ensure that everything will be good during typical operation, and rather than turning on blower fan, headlights (as Xenons can cause lots of noise) etc etc we have been using 2 methods:
1. A carbon pile battery tester (ie to load the alternator with 30-50amps at the battery) and make sure the alternator output responds and can cope as well as volt drop on both pos and neg circuits.
2. Using 60w headlight bulbs (or other Wattage's as needed, or multiples there of) to simulate circa 5amp (for a 60w bulb) of current - ie to test the volt drop on a fuel pump or wiper circuit, when we don't want to run the actual component.

The issue with the Carbon Pile tester is the accuracy, especially at low amps, its great for 50amps, 100amps or more, but impossible at 5amps or even 10 amps.
The bulb solution is great, except the bright light and heat of the bulbs, along with the danger of them being broken (so it's a fragile solution).

Does anyone have any bright ideas (or simple ones!) for generating a reliable stable load without some or all of the downsides?

Thanks
Richard
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Re: How to create reliable stable Current Drain

Postby Avdr » Fri Jan 25, 2013 12:35 pm

You cannot escape heat output with any resistive load. For a cheap initial solution you could start using electric elements from other devices. ie. toaster, kettle, hair drier. Or go to power resistors and big rheostats.
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Re: How to create reliable stable Current Drain

Postby FioranoCars » Sat Jan 26, 2013 6:43 pm

thanks, some food for thought.

Heat we can deal with, provided the current remain stable, so I'll have a dig about the scrap and see what we have. I guess an old motor would be a good bet, and a simple potentiometer might even give us a variable source!

Maybe an old drill ? An 800W motor would drain about 60amps at 13volts

If anyone else has any thoughts, ideas please let me know!
Thanks
Ricahrd
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Re: How to create reliable stable Current Drain

Postby Avdr » Sat Jan 26, 2013 7:37 pm

A large AC motor will have virtually no resistance. As far as I know, once they get turning you get the back EMF opposing the supply voltage, which limits current. But when used on DC its not going to turn.

Would stick to things designed to heat, rather than rotate. A pure resistive load is going to be most suitable.
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Re: How to create reliable stable Current Drain

Postby FioranoCars » Sat Jan 26, 2013 8:56 pm

On the motor front was thinking cordless drill, but I see what you mean.
Will look at other ideas

thanks
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Re: How to create reliable stable Current Drain

Postby FioranoCars » Sun Jan 27, 2013 11:38 pm

I think I have the solution!

Found some 120W 12V water heater elements (used for camping/car) as mug style water heating elements, for peanuts. Ordered 2 to check their consistency and build.

So circa 10amps per element, and the reviews say they take forever to heat the water (all the better, don't want to have lots of boiling water), so provided they have a stable current draw (we'll test before using), then we might have a simple and hopefully constant current draw.

If all goes well then 5 units individually switched will give a 10-50amp (aprox) current drain.

Also found a potentiometer controller board with LED (0-100%) that will cope with over 20amps, so no issue for 10amps, that will provide a very simple ability to make the 120watt element become a 1%~ 0.01amps / 10% ~1amp to 100% ~ 10amps (ie simple decimal place provides an aprox AMPS reading). This is coming from China, so a few days/weeks to arrive no doubt, but will post results when it all comes.
Only 1 unit needs a potentiometer to get a 0-50amp range variable current drain, exactly what is wanted. All for less then £50!

Hopefully the Heat can be managed by a suitable sealed "pot" of liquid, reducing all the side effects that currently cause concerns, at least for a 10minute maximum continuous operational cycle.

More on the outcome in a few weeks when it all comes together ... fingers crossed!
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Re: How to create reliable stable Current Drain

Postby Avdr » Thu Jan 31, 2013 7:59 pm

Glad to hear you've found a solution, hopefully it works as you intend. Keep us informed with how it goes.
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Re: How to create reliable stable Current Drain

Postby mteste03 » Wed Feb 06, 2013 12:28 pm

Hi,

Did you try the heating element; I would expect the current draw to change dependant on temp?

Also have you looked at the teslite pro for loading testing?

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Re: How to create reliable stable Current Drain

Postby FioranoCars » Sat Feb 09, 2013 12:29 pm

Hi Matt

Yes, tested 4 elements, none even close to their sellers quoted rating, all those quoted at 120W (ideal rating for us on circa 12v) are really 70-90w (6-8 amps roughly) and a couple of 200W, more like 110W~9amps.

I have a controller with 0-100% potentiometer with LED capable of driving 300W so comfortable range for 130W (my ideal mid point for getting close to 10amps). I Will look to try and balance up one of the units close to 10amps, to give a range of 0.1amp to 10amps load.

Clearly testing a car with engine on and a running alternator generating 14+v verse an Engine off with mid charged battery of 12.5v will have a small offset (about +/- 5% from target) but that's not an issue, this is meant only as a in the field bit of kit not a laboratory machine!

But hopeful that once all the bits are assembled and tested it gets close to the projections! Need to test the controller and find a box to put it in, along with a box for the element to hold some fluid to keep it all safe!

The Teslite pro
Yes a friend has one, though not seen it in the flesh. Sadly it works on a roughly 0.5amp test, which will not tax an alternator! indeed it will not really help test fuel pumps wiring (or other 5-15amp circuits), as often it is only after some running and heat that faults occur (lifting tracks/Bi-metallic type heating/cooling faults).

For what they are (and the price) they make a great tool, along with a PowerProbe3 (or a Hook when it finally comes along to market - did see one in the flesh, cool tool!) though even the hook does not have a Testlite style load feature (shame). A testlite is easy to make too, just a resistor (even a bulb or re-use an old light up style test probe - probably what I'll do when I have a few minutes to spare!).

The goal is to make a bigger load, say up to 60amps, for alternators testing under load (shows lots of failures normal testing misses) ...
but for other circuits really 90% are only 0-10amps, 8% 10-15amps and 1% 15-20 and less than 1% 20-30amps. I'd just like to have the full range of testing available!

The reason for the artificial load is when the device are impossible to run safely (F1 pump, fuel pumps etc) during testing, or where the device is dead and the wiring needs to be tested before a NEW unit is connected.

Just remember before trying this at home, the ability to blow ECU's and burn wiring harnesses/Fuseboards by improper use is very high! If you DON'T understand a circuit FULLY, don't load it with AMPS!

Will take some pictures of the prototypes and finished unit as it is built.
I guess this whole idea/project is pretty niche, but having had over a dozen occasions needing something, it was time to do it. It's been a learning process too which has helped in many other ways, so it's been fun and beneficial too

Richard
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Re: How to create reliable stable Current Drain

Postby Avdr » Sat Feb 09, 2013 6:17 pm

Considered glow plugs?

And immersed heater elements, as found on many CRD's?

Should be tighter on the tolerances.

How are you managing to test circuits without still going through the car fuses?
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