Adapter / Charger mA rating?

[DiodeDude]

Hi All!

I recently bought one of those emergency/portable Crank-to-Charge radios..... It'll run on the re-chargeable battery pack OR 3-AAs. You can also plug it in with a 6V adapter & charge the batt pack. The adapter did not come with the unit???

I see that there are various "Universal" adapters available in electronics stores. The manual with the radio says adapter should be 6V/200mA. Adapters available locally are significantly higher, (800mA, 1600mA etc.)

If a higher rating like this is used, will it affect the charge time? I would think that the rating of 200mA is stated so that there is sufficient current to charge in a reasonable time period & having a higher rated adapter will not necessarily reduce the charge time.... Long, slow charge is better then fast?

I rather suspect that the unit will only draw what it normally needs. The remainder of a higher rated adapter/charger current would only be reserve for higher current applications. Hopefully an adapter with this much higher rating will not damage the radio/batt pack?

Comments/ feedback appreciated!

DD

 

[Willbe]

The manual with the radio says adapter should be 6V/200mA. Adapters available locally are significantly higher, (800mA, 1600mA etc.)

Use a shunt resistor?
For the 800 mA you want to shunt 600 mA, so 6/0.6 = 10 Ω at 7w.

 

[Leftyretro]

"I rather suspect that the unit will only draw what it normally needs. The remainder of a higher rated adapter/charger current would only be reserve for higher current applications. Hopefully an adapter with this much higher rating will not damage the radio/batt pack?"

I suspect your correct and a higher current rated adapter should work fine. Certainly the charger current limit is set internally rather then somehow relying on the adapters maximum capabilities.

Lefty

 

[Willbe]

6v @ 200mA, so the load is 6v/0.2 = 30Ω.
Let's say it goes 15% higher (to 6.9v) under no load so the internal resistance is 0.9v/0.2A = 4.5Ω.

For 6v @ 800mA and the same 15% the internal resistance is 0.9v/0.8A = 1.13Ω. This supply would put 6.9v(30)/(1.13 + 30) = 6.6V into your radio, the equivalent of your 6v 200mA unit at high line voltage. If your house is close to the pole transformer you might already be at high line, so the 800mA unit will go even higher.

To have the same 4.5Ω internal resistance the 800mA supply would have to go to 10v, unloaded. That seems a bit high.

At best you'd be shortening the service life of the downstream components.
The price of the 10Ω resistor is the premium you pay for long-life-insurance for your radio.

 

[ismaelcantu84]

i have a question. i want to build or put together a rechargable battery from scratch that i can recharge via usb = 5v or a hand dynamo and solar panels. What kind of battery can i use for this. I want it to be very small. Also the real question is how do i get it to charge safely as far as not burning out the battery or causing it to leak. I have been able to pull this off, but i have to be disconnect the battery and keep a close watch. My question is what do i use so that when the battery is fully charged it stops taking in a charge. Also is it safe to charge it with different voltage as far as the hand dynamo and solar panels are concerned.

 

[Hero999]

It probably uses a constant current charger so it will make little difference whether the voltage is 5V or 8V.

If in doubt use a regulated adaptor.