O.K. to charge NiMh batt's inside Uniden scanner w/internal charge circuit?

[Stu]

Hi all-

This isn't flashlight related, sorry if wrong forum section for posting.

I have a (four AA battery) Uniden scanner that has a switch inside the battery compartment.. one side is for alkaline use, the other option will charge ni-cad batteries if the unit is also plugged into a wall outlet or 12v lighter socket.

I picked up some 2500 mAh NiMh batteries (Digital Concepts, with 1-hour charger) and would like to occasionally top them off inside the scanner by using the power cord, if it won't harm anything. Perhaps the internal charge circuit puts out a relatively low current that the NiMh can "safely" withstand?

For now, I'm just charging them in the wall charger and installing like regular batteries. The scanner manual doesn't explain how the internal charge circuit works (don't know whether it's timed only, variable, constant trickle, or the current amounts), and no mention of NiMh anywhere. I suppose the safest thing is to continue external charging and just be happy with that. I don't want to overcharge them inside the scanner if that's a potential risk. Any thoughts?
I've looked on the internet & can't seem to find a definitive answer.
Thanks

 

[macdude22]

I don't know the answer but I have a similar question. I have a Midland 75-822 handheld CB that comes with a 6 AA holder for Alks and an 8 AA holder for rechargeable. The manual lists no information on how it works, timer, smart, etc... I've yet to use the feature because I don't want to melt 2 packs of Hybrids in it overcharging but it would be super useful if I could just plug it in and go. I emailed them once but never got a response. If anyone has any knowledge of this product as well it would be helpful.

Don't mean to hijack your thread but it seems odd how such a useful feature on these devices could be so poorly documented.

 

[Stu]

Hey, macdude.. great point you made, it's a good general question. Whether it's flashlights, scanners, CB's, whatever electronics.. I don't know why answers to this type situation seem to be unclear or a bit hard to find.

 

[Mr Happy]

In general a NiCd charger will also charge NiMH cells, but there are a few specific things to watch for.

If the charger applies a low current on a timer before cutting off, then this may not be enough to fully charge typically higher capacity NiMH cells. It may be necessary to run the timer a second time.

If the charger applies a low current continuously without ever stopping, then leaving the power connected after the NiMH cells are charged may cause damage from overcharging. In such a case you would want to find out how long it takes to fully charge the cells and unplug after that.

If the charger uses some form of intelligent charge termination you should be good to go but you would be wise to test first. Make sure the cells don't start getting hot and staying hot at the end of charge, since this would be a sign of missed charge termination.

In any case, it would always be best to pull the plug after charging is complete just to be on the safe side. Either run the unit on battery power, or on the mains with the batteries removed.

 

[Ray_of_Light]

In my experience, equipment with alkaline/rechargeable switch drive a constant current of 50 - 100 mA through the batteries - when the power is applied.
Usually, they use a very simple circuit, made with a diode and a resistor. I doubt there is a charge termination circuit, or even a charge timer in your scanner.
I would install Ni-Cd batteries and not Ni-MH, since the latter are prone to failure under continous overcharge.
If you want to use Ni-MH, take a measurement with a multimeter of the charging current, and unplug the scanner after charge is complete. I mean, if you measure a charging current of 0.1 A, unplug the scanner after 30 hours of charge.

Hope this helps.

Anthony

 

[N467RX]

I wouldn't. Simply because you get a faster & better charge in a charger, and if something goes wrong, it is cheaper to replace a $30 charger than a $200+ scanner.

 

[phenwick]

The BCD396T has a timed charger. There have been many reports (radioreference.com) of the scanner getting very hot when the batteries are charging. So most users turn the charging circuit off and use an external charger, swapping out sets of batteries, using high capacity Nimh. The risk of damaging the scanner if a battery goes south from overcharging is the main concern.

 

[Eugene]

I have the same midland cb and have pulled the small charging pcb out, its a simple trickle charger so I charge my eneloops outside of them. I keep looking through spec sheets of single chip NiMH pack chargers to see if I can build a small enough circuit that will work.

 

[TooManyGizmos]

Also ... Some scanners such as Bearcat 246 and 250D say in the documentation to only insert and use rechargeable batteries that have 1800 mAh rating ...... I assume they mean not to exceed that with 2600 mAh batteries ?

In my experience , the batt's AND the scanner stay Quite warm .... All the time .... while conn. to wall-wart.

On my 250D , the digital Display is much dimmer and hard to read if I don't leave the batt's in all the time while on wall-wart power.

 

[Stu]

Thanks for the replies, everybody.
I think I'll follow the advice of external charging for day-to-day usage.. it's for sure quicker and less worry about possible damage if internal charging inadvertently goes on too long. Also, it just makes sense to get an extra set of batteries to recharge for only an hour or so to reach full capacity, and rotate as needed.

 

[Eugene]

I thought the general consensus on radio reference was that the charging circuit was a simple trickle charger.
We bought a pair of cordless phones less than three years ago and the NiMH packs in both of them last about 50% of new due to being trickle charged all the time. If they are going to use such a simple charge circuit its actually better to use nicads since they tolerate the overcharging better.

 

[Stu]

I thought the general consensus on radio reference was that the charging circuit was a simple trickle charger.
We bought a pair of cordless phones less than three years ago and the NiMH packs in both of them last about 50% of new due to being trickle charged all the time. If they are going to use such a simple charge circuit its actually better to use nicads since they tolerate the overcharging better.

That's really interesting.. since I've just recently started using rechargeable batteries, I've seen a few remarks here and there about ni-cad tolerating continued charge better than NiMh. I wonder if the "memory" issue is still something to consider with the ni-cads that are new in stores, If not, it may be worth getting some and let them stay on a trickle charge when it's convenient.

 

[SilverFox]

Hello Stu,

You may find this thread informative...

Tom

 

[Eugene]

yea, the memory effect is almost non existent.
that being said, I prefer to standardize and don't want to have one piece of gear running nicad while the rest have eneloops in them so for now I charge outside of any of my gear that has internal chargers. i don't use my scanner often so it works out ok.

 

[phenwick]

Here is a quote from this thread at radioreference.com

I would not fit 2000 mA batteries to a 396 full stop.The charging circuit was designed to charge the supplied 2300 mA types.2000 mA will be overcharged ,batteries of more than 2300 mA rating will be undercharged.Remember the internal charger is a timed charger,14Hrs for 2300 mAh,230 mA charge rate.
Just use a good external charger to stop the concern folks.

Search rechargeable in the uniden thread for more info. The BCD396T uses a 14 hour timed charge.

hope this helps.

 

[Stu]

Thanks again for the references, everybody.