mA Rating of Charger Adapters

[DiodeDude]

HI:

If anyone is knowledgeable along these lines..... I have a device that uses a 6 volt 450mA adapter to recharge built-in rechargeable batteries, Is it better to go with a higher or lower mA capacity adapter if a 450mA is not available? I would have figured that more is better than not enough. The device will only draw what it normally needs? I you go with a lower mA model then there would not necessarily be enough current to charge in reasonable time period?

Knowledgeable feed-back appreciated very much!

DD

 

[dknguyen]

THis is the power adapter right? That supplies power to the charger? Yeah, go higher since having more capacity is better than having too little. Remember those ratings are for capacity. 450mA means the adapter will supply whatever the load requires up to 450 mA.

If it is the charger itself, it's always better to pick a lower charging current since that is safer if you do not know what the limits of the battery are.

 

[Sceadwian]

Be very careful you're able to differentiate between a power supply and a battery charger. The charger for many NiCad and NiMH powered rechargeable devices are nothing more than carefully rated power supplies and choosing one with a higher ma rating than the one the pack was designed for will likley result in overheating, cell life reduction/damage, and be a fire hazzard. Cheap 'chargers' rely on the rated ma output of their power supplies to cause a voltage sag that will stop the charging current gradually as the pack reaches capacity, a higher ma rated pack will keep it's voltage nominal past the safe charing current of the pack and cause heat which destroys batteries and is possible to start fires, this is especially true of lipoly batteries, which experiance overheating 'harder' and their energy density allows thermal runaway to cause the pack to burst into flames when not intelligently charged.

 

[DiodeDude]

Power supply only?

I am pretty sure this needs a power supply only since you can also run the device (small portable, hand crank radio) on the 6 volt adapter. The battery pack is a 3.6V NiCad similar to one you'd see in a cordless phone. If the radio takes a 6V DC in adapter then the charging circuit/logic would have to be on board the radio (to charge the 3.6v battery pac.) Else they would specify greater details on the adapter required than just 6v 450 ma.

Thanks!

DD

 

[Sceadwian]

That sounds sane, but I'd take the whole thing apart and snoop around to see what's what first, if it doesn't implicitly state a higher capacity power supply is safe then assuming such is at your own risk.

 

[DiodeDude]

Keep an Eye on..........

Well I would be sure to charge it under strict supervision for the 1st few times - Keeping an eye to the battery temperature. I could easily put a meter in there to monitor volts & current over charge cycle also.

I doubt I would ever leave it plugged in over long periods or when not attended. It also runs on reg AA's.

Oh & I also asked about this on the manufacturer's Technical Assistance website. They replied: OK if voltage is the same.

DD

 

[Sceadwian]

Sounds safe then.

 

[DiodeDude]

Universal solution!

Yes I think I am gonna try the Universal 6V adapter from The Source (Canada.)

**broken link removed**

It is a 800mA model but has a regulate 6v output! This will provide a constant 6V even though the radio will draw much less current than the max of the adapter.

Thanks Sceadwian et al!
DD

 

[DiodeDude]

What's a "lipoly" battery?

Sorry if I haven't been paying attention?...... But What's a "lipoly" battery?

DD

 

[Speakerguy]

Lithium polymer.

 

[audioguru]

A Lipo battery is a Lithium-ion polymer type. It has a high capacity and less weight than other battery types.

Lithium is a very active metal and if the battery is charged to a voltage higher than 4.2V then a chemical reaction inside it causes it to ignite.
If the voltage is less than 3.0v then it is unstable and might ignite unless the charging current is reduced.
If it has a load current too high then it will overheat and ignite.
Water on its fire causes it to burn hotter, like magnesium.

Google has many videos of lithium battery fires.

 

[Speakerguy]

Also never use a LiPo battery if it appears 'puffed' up or out.

Over charging (Vbatt>4.2V) over discharging (Vbatt<3.0V) are big no-no's as is drawing more than what they are rated at. I think the latest are rated at about 20C, but you should try to stay well under that as some are max 8C discharge where C is rating in mAH.

 

[DiodeDude]

No Worrys re Lipoly!

Thanks for the additional info on same. No worries here tho since this one is a 3.6V NiCad pack as discussed above.

DD