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Message started by kamelryttarn on 04/17/20 at 05:43:09

Title: Built a battery tester
Post by kamelryttarn on 04/17/20 at 05:43:09

To take a break from understanding how the engine is put together and how much I need to take apart to replace my cam chain I took some parts I had lying around and built a battery tester for the starter battery instead. Felt good to fiddle around with something I actually understand.

The micro controller counts down by blinking one of the LEDs then it activates the IXYS mosfet module beside the green pcb for three seconds, simulating the starter of the engine.

Title: Re: Built a battery tester
Post by kamelryttarn on 04/17/20 at 05:48:32

The battery is connected to 6 power resistors 3 Ohm each creating 0.5 Ohm. When verifying with the oscilloscope I could confirm the current and the voltage drop of my starter battery.

When my bike was actually running I measured the current when I ran the starter circuit (including the decompression solenoid) and got around 20A so this should work well as a dummy load to check if the starter battery is ok.

Title: Re: Built a battery tester
Post by Armen on 04/17/20 at 06:33:55

Very cool!
I have one of those battery testers with a huge variable load/heat sink thingie in it. Owned it forever.
Hardly ever use it.
On electric start bikes, I just attach the voltmeter to the battery and watch the voltage drop during cranking. No heavier load on the system than the starter.
If the battery drops to 10v, it's probably dead or dying.
Then I see how fast the battery voltage recovers. Do a few cycles of starting, letting it run at about 2K revs for a bit, then see if the battery voltage (at rest) has dropped significantly.

Title: Re: Built a battery tester
Post by stewmills on 04/17/20 at 07:03:49

Wow! I would have gotten as far as soldering the clamps onto the lead wire and then it starts getting over my head.

Smarty pants! :P

Title: Re: Built a battery tester
Post by kamelryttarn on 04/17/20 at 07:21:18

hehe these are the things I am fairly good at. Tightening bolts and measuring valve clearance and loosening things that are stuck... not so much

Title: Re: Built a battery tester
Post by eau de sauvage on 04/25/20 at 18:08:07

@kamelryttarn, are you saying the S40 only draws 20A starting up? I find that hard to believe. Do not we look for around 200CCA when purchasing a battery?

Wouldn't it be easier to test the battery under normal starting load. I haven't tried it with the S40 because it's too annoying to get to the battery but on my GS500 I watch the voltage drop when I turn the lights on, then I use my phone to take a movie of the voltage drop as I crank it over. You need the movie because you only get a moment to see it, and it's easier to just play it back to check more accurately. The starter motor wants a couple of hundred Amps for a second. The battery might look good but still drop to 10V when starting which would indicate it's gone in spite of seeming to be good. I get worried if it drops to 10.5 while starting. I'm not an electrical engineer but it makes sense to me. Especially as I got stuck one day when what seemed like a perfectly good battery, suddenly when stone cold dead.

Edit: just checked the standing voltage and it was 12.3 under starting load for a few seconds it was able to hold 10.8V so I conclude the battery is fine and just needs a top up charge. Below 10V for a few seconds and I would begin to worry.