Did you get a NiMH charger at the same time?
It sounds like the trimmer takes quite a bit of current. Maybe your supply was not big enough. How many amps?
Hi all!
I have a hair trimmer which is powered by an AA NiCd rechargeable battery. Over time the battery's capacity went too low. The trimmer still works with it but only for a short time, and then the battery has to be recharged, which takes about 10 hours. This is very inconvenient, especially if one only managed to trim, say, one side of a head.
So I really need an alternative power source. I tired to use one AA NiMH battery with a capacity of 2700 mAh, but it does not work well: while the motor is powered up and rotates when blades are detached, with the blades attached it does so only occasionally, suggesting insufficient power.
The strangest part is that even after I connected in parallel four AA NiMH batteries each with capacity of 2700 mAh, they still were not able to power up the trimmer efficiently, performing only slightly better than one NiMH battery. And the old and worn-out NiCd battery still powers up the motor with the blades every time it is switched on.
Also I have a power supply which can produce 1.6 V voltage, but when I connect it to the trimmer and switch the motor on, the voltage drops to almost 0 V.
1) Can anybody explain why do four NiMH batteries connected in parallel under-perform one NiCd battery?
2) Is it possible to assemble a circuit to power up the trimmer with one NiMH battery?
3) Is it possible to power up the trimmer with a power supply?
Thank you.
I think you have come across an interesting fact. It would appear that the two difference battery chemistries can both absorb about the same amount of overcharge level based mostly upon their physical cell size and not the cell capacity. Thus I think it unlikely to be a random coincidence.A Ni-Cad battery can be continuously overcharged at 1/10th its capacity. An AA cell is 600mAh so it can be overcharged at 60mA continuously.
A Ni-MH battery can be continuously overcharged at 1/40th its capacity. An AA cell is 2400mAh so it can be overcharged at 60mA continuously.
Is it a coincidence?
Hi, guys!
Thanks for your help. I also think that NiMHs should perform just as well as NiCd, and that is why this is so weird that they do not. If we all assume that they should, then let's call this troubleshooting, since the trimmer still turns on with NiMH only occasionally.
I would buy of course a new NiCd, if only I knew that that particular kind would work. But how can I know that if the battery inside the trimmer does not have any markings regarding its brand or type. There is a marking "SAN 06-01 S", but I was unable to find anything in the Internet using that.
The blades can be detached, and then the motor can spin without any mechanical load. The blades seem to get a little stuck in certain positions, and to move them from those positions requires extra power from the motor. The NiCd seems to be able to provide that extra power to the motor, while four NiMH seem not.
I found the following passage in Wikipedia: "With a relatively low internal resistance, a NiCd battery can supply high surge currents. This makes them a favourable choice for remote-controlled electric model airplanes, boats, and cars, as well as cordless power tools and camera flash units."
Please note the words "favourable choice". And this is despite their memory effect and the bad ecology.
I did some measurements when the trimmer is powered from four NiMH batteries:
----------------------------------------------------------------------------------------------
.........................................................................current...........voltage
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Off.........................................................................-................1.34 V
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On, with blades, but unable to move them.............1.95 A...........1.20 V
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On, without blades, motor rotates ..........................0.50 A..........1.31 V
----------------------------------------------------------------------------------------------
On, with blades, blades are moving........................1.30 A..........1.26 V
----------------------------------------------------------------------------------------------
If I short circuit the four NiMH batteries, they produce current 6.0 A (6.5 A when they are freshly charged).
How could this current not be sufficient to move the blades ?????
Today I replaced the connector, it did not help. It does not seem to be the problem with wiring since I measured also the voltages inside the trimmer, they were very similar for both NiCd and NiMH, so there was no notable drop. The wire gauge is 0.75 mm, which should be Ok.
Carl, mine is also Norelco. Do you by any chance remember the brand and specific type of the NiMH battery which worked for you?
I am just so perplexed. Today I started to think that there might be a curse. Either I am cursed or Philips is. Or China.
How can I troubleshoot this? What do I need to check? Any ideas?
Also, is it difficult to assemble a power supply that could power up this trimmer? I already have a spare transformer and some parts.
Or, say, is it possible to modify the "500 mA" power supply to this end?
Thanks for your patience and help.
Energizer's datasheets show that their AA alkaline cell has 10 times the internal resistance of their Ni-MH cell so it is no good at high currents.... did we ask him to try a brand new fresh alkaline yet? That would be a nice test to see.
Many shavers use fairly low current so they can be run from ordinary alkaline cells. But Ni-MH cells have a much lower internal resistance (it is low even when half-discharged) so they can supply much more current.Hello again audioguru,
10 times sounds like a lot, im not so sure i believe that data. I've run several shavers off of AA alkalines (not AAA though) and they all ran fine. Maybe he's got a Herman Munster shaver
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