Wireless Mains Adapter-Frequency etc.?

[boiss]

I'm going to knock up a system to charge the batteries and power the radio (Hacker Sovereign) wirelessly. (My radio has no socket for external power and I am not going to modify it) This will mean that the radio must be put in a cradle or on a plinth for the system to operate. One thing I have been thinking about is the frequency to use because this will be quite a powerful signal (around 20W). Keeping away from frequencies that multiply up to the IF is the obvious one, but are there other frequencies to stay away from? In the Hacker instance there are 2 batteries, while each will have 6 nicads, they will also need their own coupling/charging cct.
Due to the high cost of power microwave devices I guess this system will need to work in the LF region 25KHz to 150KHz.
Any suggestions, has anyone done this already for their equipment/radios?
Mike

[pwdrive]

When you say wirelessly do you mean the 20 watts of power will be inductively radiated?

Lawrence.

[Yorkie]

Just a point, presumably you use your Hacker several hours a day on a daily basis?

If not, nicad cells (or NiMh for that matter) are a poor subsititute for conventional batteries as they self discharge when not used. Fine for such things as radio controlled model cars and boats, portable amateur radio transceivers (go on then - 'walkie talkies!'), as they draw quite a lot of power and the cells then be re-charged before the equipment is next required. Self discharge is why I'm not a huge fan of cordless tools - I've got several rechargable drills, some of which use LiOn batteries, but still self-discharge as I use them so infrequently, so I have to give myself a day's notice to recharge them ready for use. (EG, when I go to either of my son's houses to do a spot of DIY).

Can't comment on the concept of wirelessly charging the cells, though if the Hacker is indeed in regular daily use, maybe it would be less hassle to just have a spare set of fully charged cells waiting to be used, then put the discharged ones on charge. That's what I do with my wireless mouse, in which the two cells last about a month.

As to the frequency, whatever frequency is used, you'd need to be careful about the risk of causing RF interference on the fundamental or harmonic frequencies, as of course such equipment is unlicensable. It's one thing using a puny illegal 'micro-transmitter' ('pantry transmitter') - unlicensable within the EU - which puts out perhaps 0.5W over a short distance, but it might be problematical if you squirt 20 Watts out, remebering that the amateur radio Foundation Licence, which is limited to 10 Watts, will get contacts the world over with a good antenna system.

A receiver would be needed to convert the transmitted RF power to enable it to recharge the cells. Well outside my sphere of competence - sounds like a project for Nicko!

Just a few musings - I certainly wouldn't want to discourage experimentation and will be interested in any developments.

[camallison]

I'm going to knock up a system to charge the batteries and power the radio (Hacker Sovereign) wirelessly. (My radio has no socket for external power and I am not going to modify it) This will mean that the radio must be put in a cradle or on a plinth for the system to operate. One thing I have been thinking about is the frequency to use because this will be quite a powerful signal (around 20W). Keeping away from frequencies that multiply up to the IF is the obvious one, but are there other frequencies to stay away from? In the Hacker instance there are 2 batteries, while each will have 6 nicads, they will also need their own coupling/charging cct.
Due to the high cost of power microwave devices I guess this system will need to work in the LF region 25KHz to 150KHz.
Any suggestions, has anyone done this already for their equipment/radios?
Mike

If you know anyone with one of the Oral-B rechargeable toothbrushes, you might "sniff" around that and see what frequency they use. Unfortunately, the only one we have has already been hacked by me, and won't repair. They have a coil in the base and a similar one on the toothbrush handle that couple to transfer the power. Looking at the one in the toothbrush, it is a few hundred turns with a centre tap. The converter/charger circuit is tiny with SMD chip and other components. The chip type info has been covered with "goop" so I can't see what it is.

The cell that is recharged in this case is a NiMh 3/4 AA-size cell. Later models have a Li-ion cell instead.

Colin

[UPDATE - found that SWMBO has bought a new one and, on pain of untold agonies if I broke it, I have sniffed around the base charger and the frequency is 100Hz with a fair amount of harmonics too. Obviously it would need some extensive scaling up for the Hacker set.]

[Eddystonepete]

Hi Mike, I like simple things. What about using 2 small mains transformers, 1 outside powered by mains, the other inside feeding a rectifier. Maybe the one inside would not need a core, not sure of the theory. I think the RF route would be fraught with difficulties. Peter

[pwdrive]

Is there any spare in/out sockets you could rewire for dc input?

Lawrence.

[Refugee]

I would check what fittings are already there.
The handle fixings come to mind. The charger would then be two hooks that the set is placed on while charging or listening. A simple microswitch would be fitted to shut the charger off when not in use.

[Radio Fixer]

Alkaline cells are fantastic. I have had radios with batteries 10 years old that still work for occasional use. Now you can get rechargeables as well.

Lion is great in my opinion for cordless tools for instant jobs! With there high torque, freedom from running leads that are usually tangled and a danger up steps or ladders. Mine remain with chargde for weeks and I put one on charge as soon as I start a job. Seem to charge quick as well, certainly don't need a days notice as said by David. Maybe as they get older this may not be the case.

Gary

[Eddystonepete]

Hi Mike, tried the transformer idea I suggested with very poor results! Sorry!. Using the handle screws sounds good. Peter

[Nick]

Wireless power transfer is tricky to do efficiently. In another (parallel) life I do a lot of HV/HVRF stuff - over on 4hv.org this is a topic that we've discussed ad nauseam - if you really want to go the RF route, you need to read the (nice example project) thread at:

http://4hv.org/e107_plugins/forum/forum_....php?74096

I'm not convinced by the mains transformer option... personally, I'd probably make a small SMPS to fit inside a dummy battery pack...