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FrozenGate by Avery

Need to reduce dc current by 0.7volts

rpaloalto

rpaloalto

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Ok, so I just bought a really sweet Sanyo 18650 cell from LarryDFW
It is one of Sanyo's newer cells, rated at 2800mAH:)
Unfortunately it requires a 4.3v charge, instead of the standard 4.2v to take advantage of it's true 2800mA capacity
http://battery.sanyo.com/en/spec/ion/UR18650ZT.pdf


Anyway I have several usb chargers that are rated at 5v 500mA
Cant I just use a resistor to drop it down to 4.3v

If so, what kind or how many. The people at radioshack are of no help I just came from there:(

The usb charger I have puts out exactly 5.04v

Thanks
 





You could use a single sillicon diode to drop a voltage, but to charge a battery is more complex than just connecting it to a DC power supply - you have to limit the current, amongst other things. You'll also find that running at 4.3v could shorten the battery lifespan. If you can't make do at 4.2v, or find a reasonable 4.3v charger, then you'll have to work out a current limiter as well as voltage limit.
 
rpaloalto said:
Ok, so I just bought a really sweet Sanyo 18650 cell from LarryDFW
It is one of Sanyo's newer cells, rated at 2800mAH:)
Unfortunately it requires a 4.3v charge, instead of the standard 4.2v to take advantage of it's true 2800mA capacity
http://battery.sanyo.com/en/spec/ion/UR18650ZT.pdf


Anyway I have several usb chargers that are rated at 5v 500mA
Cant I just use a resistor to drop it down to 4.3v

If so, what kind or how many. The people at radioshack are of no help I just came from there:(

The usb charger I have puts out exactly 5.04v

Thanks
Click to expand...

Hi John,
You might want to reword your title.
Current is measured in Amps, not volts.
You shouldn't do anything to your charger. It is made to apply a higher voltage than the battery needs during charging. You can try some of your other chargers as they will differ just a bit from one to another.
This 0.1V difference isn't going to make any real difference as under a load it will drop that much in a matter of less than a minute. There are other parameters that matter more, like exact room temperature, did they specify the temperature. Another important one is load, they will usually specify an applied load that they used to come up with their rating, it's probably not a big load either.
I would guess that the 0.1v diff would hardly make any impact compared to the room / battery starting temperature and the load.

Let us know what you find.
 
Sorry John you can not do this ! A lithium charger is different from other chargers it measures the charge and voltage constantly, I have a Lipo charger for 18650's if you need one.



rpaloalto said:
Ok, so I just bought a really sweet Sanyo 18650 cell from LarryDFW
It is one of Sanyo's newer cells, rated at 2800mAH:)
Unfortunately it requires a 4.3v charge, instead of the standard 4.2v to take advantage of it's true 2800mA capacity
http://battery.sanyo.com/en/spec/ion/UR18650ZT.pdf


Anyway I have several usb chargers that are rated at 5v 500mA
Cant I just use a resistor to drop it down to 4.3v

If so, what kind or how many. The people at radioshack are of no help I just came from there:(

The usb charger I have puts out exactly 5.04v

Thanks
Click to expand...
 
I just figured I could charge it at the 4.3v and just check it every so often with my DMM until It reached 4.3v, Probably in my garage in a bucket or someplace safe.
 
Last edited:
If you do do that, you better ALWAYS charge them outside somewhere safe, well ventilated, and fire-resistant. Perhaps under an overturned bulky flower pot.

Really, the best and safest bet is to buy a charger specifically made for that chemistry. I couldn't find out more about these, but I think they are normal LiCo cells, so just get a normal Li-Ion charger. It should be at 4.2V when the charger terminates.
You may need a different charger for LiMn.

Even with a suitable charger, you should charge in a safe area, although probably not as extreme as if you were charging by hooking up a cell to a "usb charger"

Edit: oh, I guess I should make this post relevant to the thread by saying "you can use a run-of-the-mill silicon diode to drop the extra voltage. 1n4000 series generally drop between .7V and 1.0V and can usually handle anything under 1A"
 
Last edited:
I know the difference between 4.2 and 4.3 is not much, but according to some tests done by a CPF member. Showed that by not charging this sanyo cell at the stated 4.3 volts only gives you 80% of the batteries full capacity. I want the full 2800mAh out of this little bad boy.

I just figured I could gut one of my many DX 18650 chargers. And hook up a USB charger I have, that is currently putting out 5.04v at 500mA. All I would need to do is drop it by .10-.07v. giving me 4.3 to 4.304.

I understand the dangers of li-ion. The charging proses would be done in the garage on the concrete floor or in a steel bucket. I would monitor the battery closely with my DMM.
 
is 80% of 2800mah so bad? how long do you need to run your laser for anyways. not being sarcastic, just throwing out an alternitive.


michael
 
chipdouglas said:
is 80% of 2800mah so bad? how long do you need to run your laser for anyways. not being sarcastic, just throwing out an alternitive.


michael
Click to expand...

Your right, Even if the battery is only putting out 2600 or even 2700mah, thats not bad. I doubt I would really even notice a difference anyway. It's just the fact that I'll always know that I'm not taking full advantage of the battery.
 
rpaloalto said:
Your right, Even if the battery is only putting out 2600 or even 2700mah, thats not bad. I doubt I would really even notice a difference anyway. It's just the fact that I'll always know that I'm not taking full advantage of the battery.
Click to expand...


it's funny how the brain works... I totally understand. if you are safe and into experiments use the ddl driver and a wall outlet timer to make your own "safer" charger. and use a small variac transformer to get your desired voltage. and set the driver to like half or a quarter of the desired ma.

michael
 
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