DIY bench supply failed when testing starter motors at no load?

be80be

Joined Jul 5, 2008
2,058
You hit a starter with a 200 amp battery charger its going to jump to life too.
I worked in one of the best starter shops in KY. He had 2 old snapon chargers
to test starters with and test bench that you mounted the starter to test it.
It would even let you load the starter.
We fixed all kinds of starters.

80% of starter problems is dragging
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
521
So have I. However, the starter motor spins up to speed much slower than when hit with the power applied by a fully charged 12 volt car battery. On the bench, powering a starter motor with charger results in a little roll, but when hit with a battery the starter will jump off the table if not secured.
It might be dues to the current limit on the charger. If your charger has a boost setting with 100Amps or more then the starter can unleash a lot of power hence the jumping around. This is quite easily visible when testing a Diesel engine glow plug too. I have tested with those normal chargers with max 10Amps, then a cheap generic glow plug under $4 will take 35 to 40 seconds to heat up to 1600F and a good one from Bosch like close to 1900F in 28 seconds. Try the same with a car battery or the charger in 20Amps or more setting and you will see the glow plugs glow in under 10 seconds at least from the good brands like Bosch.

It's all about the max power delivery as @be80be has mentioned.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
521
You hit a starter with a 200 amp battery charger its going to jump to life too.
I worked in one of the best starter shops in KY. He had 2 old snapon chargers
to test starters with and test bench that you mounted the starter to test it.
It would even let you load the starter.
Is this by any chance those chargers with wheels (kinda looks like a movable cart)? Have you ever tried those big benchtop 100Amp chargers? I have one of those very old chargers with a 100A boost setting from Lucas. But I'm nervous to try to use it alone without a battery to test a starter. More worried about frying that selenium rectifier inside. If it goes poof, then I'm in deep trouble
 

Tonyr1084

Joined Sep 24, 2015
6,467
@Rahulk70 My charger is 10/40 amps, 6V or 12V. It's a big old box type with wheels and a handle to pull it around. It's rarely used. I have those portable battery boosters that you keep in the trunk. I charge it about every three months to make sure it's up to full charge. Gave a couple away to good friends and told them to keep charging them at least every three months. They didn't do that and now the boosters don't work.
 

MisterBill2

Joined Jan 23, 2018
9,908
An average 12 volt automotive sized battery will deliver quite a few hundred amps for a short burst, without the voltage dropping below 9 volts. The typical charger has a whole lot more internal resistance and will drop down a WHOLE LOT MORE when it's rating is greatly exceeded.
 

Thread Starter

Rahulk70

Joined Dec 16, 2016
521
@Rahulk70 My charger is 10/40 amps, 6V or 12V. It's a big old box type with wheels and a handle to pull it around. It's rarely used. I have those portable battery boosters that you keep in the trunk. I charge it about every three months to make sure it's up to full charge. Gave a couple away to good friends and told them to keep charging them at least every three months. They didn't do that and now the boosters don't work.
I guess if they are old, they must be having those Selenium rectifiers in them. They withstand quite a lot of abuse. Silicon ones don't take abuses very kindly. At least the ones I've used. Those portable boosters have a lead-acid battery inside them. You need to remember to charge them at least once in a while or the sulfation will eventually kill the battery inside. I think the newer portable starter jump packs the sie of a big mobile power bank made from Lithium-ion/lipo cells are better in that option. The best thing is lithium cells don't lose their charge for a long time. The only thing is if you live in a hot environment their life is gonna take a hit soon if you leave it in car.
 

Tonyr1084

Joined Sep 24, 2015
6,467
Yes @Rahulk70 I charge them every three months or after every use. Mine has an air compressor that I rarely use, but from time to time I do use it. It's quicker and easier than setting up my big air compressor. But yes, I do keep them charged. Told my friends to do the same - but they don't think like we do. They just assume that if the battery indicator gives them four green lights they're good to go. Years later they may still have four lights - but can't start their car. They end up tossing the units - which ticked me off. Just give it back and let someone who knows how to use and maintain them use it. Ah! Oh well.
 

BobaMosfet

Joined Jul 1, 2009
1,900
But not if the starter is sitting on a bench. It only draws high amperage like that after all of the "slack" in the starter drive is taken up and the flywheel tries to move.
No, you would be incorrect. Doesn't matter if the motor has a load or not- for a an extremely short moment of time, the motor represents itself as a dead short. Simple physics.
 

BobaMosfet

Joined Jul 1, 2009
1,900
You are telling the person who services them how much they draw?
They said they didn't know the open-circuit value. Not rocket science. Here's the simple answer. Put a clamp on ammeter on it and try it and see what it reads. Then we all have an answer specific to his situation.
 

MisterBill2

Joined Jan 23, 2018
9,908
Yes @Rahulk70 I charge them every three months or after every use. Mine has an air compressor that I rarely use, but from time to time I do use it. It's quicker and easier than setting up my big air compressor. But yes, I do keep them charged. Told my friends to do the same - but they don't think like we do. They just assume that if the battery indicator gives them four green lights they're good to go. Years later they may still have four lights - but can't start their car. They end up tossing the units - which ticked me off. Just give it back and let someone who knows how to use and maintain them use it. Ah! Oh well.
I use a set of jumper cables that I made. 22 feet of #6 welding cable. They never fail me, and they allow enough power to crank al,most immediately. In addition I carry a set of the cheap ones to give to the poor dude whose charging system can't keep up. Because that guy will need them again.
I have been asked to fix several of those small battery booster devices over the years. In every case they don't work and the battery will not hold much of a charge. And one good friend had no clue what it even was, she presumed it was a cordless battery charger. I had to loan her a real charger when her car failed.
I think that I have seen some sort of package that uses a high output chemical reaction as a short term battery. It can crank an engine on a car with a stone dead battery after about a 1 minute warm up. I think the army had some of them, nobody else could afford that technology.
 
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Thread Starter

Rahulk70

Joined Dec 16, 2016
521
Yes @Rahulk70 I charge them every three months or after every use. Mine has an air compressor that I rarely use, but from time to time I do use it. It's quicker and easier than setting up my big air compressor. But yes, I do keep them charged. Told my friends to do the same - but they don't think like we do. They just assume that if the battery indicator gives them four green lights they're good to go. Years later they may still have four lights - but can't start their car. They end up tossing the units - which ticked me off. Just give it back and let someone who knows how to use and maintain them use it. Ah! Oh well.
Some people just don't take care much if it's free. A lot of times you can see most of the people used to buy those smaller Lead Acid jump start packs. If you open up the jump pack you can see that the battery inside is usually a 12V 12Ah battery. As per specs pulled for a Yuasa 12V 12Ah battery you can see it's only meant for 75A continuous current. A lot of times these packs are good only as a boost to your partially drained battery. Similar to those 70-80A boost setting on chargers as a supplement to the weak battery. Now, I've seen people with completely dead batteries use this pack and sometimes they get lucky otherwise the multiple crank attempts will drastically reduce the life of these cells. I think getting at least one of those with 1000A instant current with 560A current continuous for brief period packs like the ones from Stanley (though they are junk as the compressor unit goes out very fast. DeWalt is much much better) is a much better option since those units have a 12V 19-22Ah battery. Those batteries can handle 360A (for 5 sec.) and can handle 100A once the engine starts to spin in smaller cars easily and may last longer. But trying to use these packs for starting a heavily discharged car battery for more than a few times a year is going to have a big effect on its life. And VRLA cells are generally not made to handle such large currents due to the lesser no.- larger plate construction.
 

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