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Discussion Starter #1
I didnt mean to single out only Decosse and Forchetto - I just wanted to be sure and get their input, amongst others.
We have a huge amount of Electrical queries on this forum and most of them involve the condition of the battery.
Historically - Lots of batteries have been replaced when its something else thats actually at fault. Also - a weak battery can throw up some confusing resuts and send the owner in many directions - lots of times to the wrong faulty component.
The advise from the likes of Decosse/Forchetto is to get the battery load tested to make sure its capable of doing its job (which by the way is starting the motor).
Some of our members dont understand that any battery is going to show 12 volts just sitting there as its just a surface charge - but may not appreciate its the ability of a battery to sustain a suitable voltage while delivering a load, that makes it a serviceable battery.
My question is : can a simple, cheap load tester be constructed at home - e.g. what could be used to simulate a starter motor load - what switch/mechanism could be used to turn up the load (increase the current draw) or could the load just be switched on.
Of course a voltmeter would be required to observe the voltage as the load is increased or applied.
I think this would be very handy to have at home as lots of us have multiple bikes and of course batteries and this would allow us to rule out the battery as the problem.
I know we can just go down to the shop and get it tested - but I get a lot of satisfaction from doing these things myself, as I know a lot of others on this forum do as well.
Let The Good Times Roll - Ray.
 

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You can often see simple load testers at garages and they appear to be nothing more than a large resistor and a meter connected to a pair of spikes spaced out to suit the usual car battery.

A more modern version can be bought for as little as $31 like this Actron CP7612 Battery load tester:



A similar but even cheaper one is this $21 Schumacher BT-100:



There are more sophisticated ones around like this GOLD-PLUS tester that works by electronically simulating a C20 discharge test in a few seconds. It gives temperature, voltage and actual Amp hour reading directly on a display. Costs over $300 though:




The schumaker can be bought for $21 from places like this:

http://www.samsclub.com/sams/shop/product.jsp?productId=prod862835&pid=CSE_Froogle&ci_src=14110944&ci_sku=sku1054386

but watch out because the likes of Sears charge double that at $43, for the same instrument. For $21 is not really worth making your own really.
 

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On a warm day, the starter load can be 60 amps. On a cold day, as much as 200 amps. So you need something of the order of a 720W load to test a battery under its normal starting conditions. 1000 W, 0.2 ohm resistor should be good. You can make that from 300 ft of 8 gauge wire, for example.

I'm not sure how the electronic testers work, but if the draw is only for a tenth of a second, you need to dissipate only 100 watts effectively.
 

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I use a digital clamp on DC ampmeter, clamp it around the battery lead either positive or negative hit the max reading button and start the bike (or try if the batterys stuffed) and see what your current reading is. fancy ones you can monitor the voltage while you try to start as well. a bit more expensive although some are pretty cheap these days at maybe $60, but good for all sorts of things around the home/workshop as it will do all the usual muiltimeter jobs as well.
 

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On a warm day, the starter load can be 60 amps. On a cold day, as much as 200 amps. So you need something of the order of a 720W load to test a battery under its normal starting conditions. 1000 W, 0.2 ohm resistor should be good. You can make that from 300 ft of 8 gauge wire, for example.

I'm not sure how the electronic testers work, but if the draw is only for a tenth of a second, you need to dissipate only 100 watts effectively.
Yes, the ones you sometimes see in garages have a huge resistor made from a concertina-like plate of resistor metal and a voltmeter. They look as if the resistance is very low, like your 0.2 Ohms for example. This sort of thing:

 

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Just tested my new shorai 18ah battery with formentioned clampon

now this is peak current and minimum voltage and was probably only for a micro second while the starter was stationary and therefore drawing max current but 270 amps at 8.6 volts is pretty impressive (thats something over 2 k watts)

 

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That's a pretty good instrument. At work we have such a DC clamp meter that can measure Amps or volts, but not both at the same time with that dual display.

I think my test department is about to get one of those (whether they like it or not), and I'm going to take it home for long-term evaluation...:D
 

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They're not cheap (kaise) but that one over 10 years old and still works a treat, would buy something less costly now days but it was a work tool when I purchased it.
 

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Discussion Starter #9
Thanks for replies - couple more questions.

Plodalong - your instrument does the trick because it shows that you do in fact have a load and the voltage that is used up suppying that current.
It also shows there isnt a short in the starter motor because the load is about what you would expect.
However - wouldnt you ideally want the bike not to start so you can see if the battery can sustain the load.
I guess the high current draw in your second post is "starting current" and the 8 volts are a result of that.
Ernesto - with one of those instruments you have shown, how would you know what load to "dial" up - assuming they are adjustable - if they arent adjustable, how could they be relevant to (say) a small motorbike battery versus a larger car battery and the different loads that would apply.
Just trying to understand things a bit.
Thanks - Let The Good Times Roll - Ray.
 

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I have access to an electronic battery tester through work. It is very good and tells you immediately everything you need to know (and a lot more you don't). However very expensive.
A trick I was taught many years ago by a mechanic, I have found to be just as effective but quick and free.
Turn on the ignition, all the lights inc the brake lifgt and press the horn and keep it pressed for about 40 sec. If the battery is weak, you will notice a change in the tone of the horn as the voltage falls. The ears are very sensitive. No change in horn tone = good battery.
 

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I have access to an electronic battery tester through work. It is very good and tells you immediately everything you need to know (and a lot more you don't). However very expensive.
A trick I was taught many years ago by a mechanic, I have found to be just as effective but quick and free.
Turn on the ignition, all the lights inc the brake lifgt and press the horn and keep it pressed for about 40 sec. If the battery is weak, you will notice a change in the tone of the horn as the voltage falls. The ears are very sensitive. No change in horn tone = good battery.
Brilliant that...you are right about the ear being extremely sensitive to changes in tone. I once used an instrument designed to find short circuits in complex printed wiring boards.

It was basically a very low resistance ohmeter but instead of a display it emitted a tone. This would increase in pitch as the probes got closer to the short circuit. It was uncanny how easy it was to use.
 

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I bet the neighbours love the horn trick, too...
 

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Some hints on battery testing straight from the horses mouth (Well the Yuasa battery manual):

Test sealed VRLA types with a voltmeter or multimeter. If the stabilized open circuit voltage is below 12.5v, the battery needs charging. For a stabilized open circuit reading, first allow the battery to remain in an open circuit condition for at least 1 - 2 hours.

LOADED TESTING:

There are two types of loaded tests for motorcycle batteries. You’ll need a voltmeter or multimeter.

Low-load test:

Basically, this means turning on the bike’s lights and taking a voltage reading at the battery.

Remember, hook positive (+) to positive (+), negative (-) to negative (-). The battery in a 12v system should have at least 11.5v DC with the lights on. If voltage drops below this levels, it’s time to charge.


High-rate discharge test:

This is the best test of battery condition under a starting load. Use a load testing device that has an adjustable load. Apply a load of three times the ampere-hour rating.
At 14 seconds into the test, check battery voltage: a good 12v battery will have at least 10.5v, If the reading’s low, charge.
 
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