Testing repaired battery charger (drill)

[Old tool guy]

While visiting daughter out of state, discovered that the batteries for her Hitachi cordless impact driver weren’t charging. 12v UC10SFL. It’s a compact driver that works well for her, so I didn’t want to buy a new tool. Did some research and learned that one capacitor is probably the problem, opened the case and the end was slightly bulged. I didn't have my vintage Radio shack Archer soldering gun with me so I decided to take it home. Because i will be mailing it back i didn't take the tool.
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Got home, got the specs for the capacitor and ordered off amazon. Pack of 10 caps for $6. Replaced the cap, reassembled, and dropped the battery in the slot, and the red charge light came on. Score one more for dad. It's a very basic charger, no green light, no flashing codes … just on & off. Seems like the light went off after 20 minutes. Since i don’t have the tool, i put a vom on it and read 12v so it should be good.
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But … i want to draw down the battery and see if it recharges. How can i do that? I can connect a 12v car bulb to the battery, would that work?

 

[whateg01]

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But … i want to draw down the battery and see if it recharges. How can i do that? I can connect a 12v car bulb to the battery, would that work?

If you draw it down past a certain point the charger will consider it damaged and not charge at all. Best, safest, imho is put it in a tool with BMS and run it until it stops.

 

[darkzero]

Are you wanting to discharge it without spending money or the least possible? You could use the bulb or a 12v motor but the bulb will take quite a while. Even if you have a pretty good size resistor load, whatever you use you will need to keep an eye on the voltage to make sure it doesn't drain too low otherwise you will cause irreversible damage.

I use this for discharging my batteries for storage cycles & other purposes. It's a load/capacity tester. You can set discharge rate & voltage cut off.

 

[Torque&Recoil]

I'm thinking you fixed it. 12v with the VOM seems to indicate that it is charged. Of course, we have no idea of the amp-hour capacity, but it's likely "whatever it was before the charger quit working". Which was acceptable.

 

[Old tool guy]

If you draw it down past a certain point the charger will consider it damaged and not charge at all. Best, safest, imho is put it in a tool with BMS and run it until it stops.

Don’t have a tool it fits.

 

[Beerhippie]

Are you wanting to discharge it without spending money or the least possible? You could use the bulb or a 12v motor but the bulb will take quite a while. Even if you have a pretty good size resistor load, whatever you use you will need to keep an eye on the voltage to make sure it doesn't drain too low otherwise you will cause irreversible damage.

I use this for discharging my batteries for storage cycles & other purposes. It's a load/capacity tester. You can set discharge rate & voltage cut off.

Cool--but where would we find such an item?

Batteries generally say to store at 60% capacity--but have no way of identifying 60% cap. How would you measure that with your rig? Can you set that with a certain goal and have it shut off automatically?

 

[whateg01]

... It's a load/capacity tester. You can set discharge rate & voltage cut off.

... How would you measure that with your rig? Can you set that with a certain goal and have it shut off automatically?

Yes

 

[Beerhippie]

I still don't understand how you determine state of discharge. Don't lithium batteries maintain a uniform voltage until nearly discharged?

 

[darkzero]

Cool--but where would we find such an item?

Batteries generally say to store at 60% capacity--but have no way of identifying 60% cap. How would you measure that with your rig? Can you set that with a certain goal and have it shut off automatically?

Can find them on Amazon & ebay but I prefer to cut out one of the distribution hands & got mine from Aliexpress. There are various models with different features, mine is an Atorch DL24.

I still don't understand how you determine state of discharge. Don't lithium batteries maintain a uniform voltage until nearly discharged?

Certainly not so. Quite the opposite, voltage level would essentially help determine the state of charge for lithium rechargables. The low voltage cutoff varies by tool manufactures, cell manufactures, & chemistry type. For storage I generally run mine down to 3.7v-3.8v per cell.

Edit: I think I have an idea of what you are thinking about. So the claim used to be, still is I suppose, is that lithium powered tools will run at the same power until the battery is depleted & there is an abrupt cutoff. While that may be somewhat true for lower current draw tools & compared to order NiCad/NiMh it certainly may seem so, I don't agree with this misconception. I can certainly tell the drop in performance as batteries are near depleted.

Same goes for the old days when it was said that LEDs run cool & don't generate heat. That was before high power LEDs existed.