Thursday, August 16, 2012

This is a test of my datacom frontfage

This is my attempt at a handy, one-stop shop for anyone interested in trying their hand at the myriad datamodes available to us....blah blah blah

Friday, July 23, 2010

Things looking up for lightweight portable power

I've always been far from satisfied with the piffling amount of operating time offered by the battery pack supplied with Yaesu's FT-817. The original (1Ah?) pack allowed no more than a couple of hours' listening and almost no TX time. I bought a 'high capacity' version from the US but found this to be little better.

Next, I tried 8 x 2900mAh AA cells in the dry battery tray. This was more successful but still not that great. On TX, the voltage would soon drop below the minimum required by the rig and an untimely (and humiliating) QRT would result. And they took an age to charge up in-situ. Taking my charger on holiday, along with all the other clobber, was 'not encouraged'.

Suspecting that resistance between the individual cells might be to blame, I bought a 2400mAh, 9.6V pack of the same dimensions as Yaesu's original. Same result.

It was clear that a battery (pack) with a higher nominal voltage was required. Options considered were 10 NiMH AA cells in a battery holder or a a gel-cell. As the aforementioned charger holds only 8 cells at a time, this would effectively mean doubling down-time when charging. A gel cell worked great, with an entire day's casual operating easily possible from a 7Ah one I have here. But it's the size of a house brick and weighs in at a hefty 2.7kg.

Fast forward to a few months ago and Richard's (G3CWI) article in RadCom, extolling the virtues of lithium-ion battery packs. On further investigation I discovered a number of 12volt packs available on eBay, ranging in capacity from 1800 to 9800mAh.

I first bought a 4800mAh pack (the blue one in the picture, above). This is a little under the size of a packet of 20 Bensons, weighs a mere 185g and cost under £16. Even though I was aware that the height was greater than the FT817's battery pack, I ordered it in the vein hope of shoehorning it into the rig, somehow....perhaps by leaving the battery cover off. At 17mm, it stands 3 or 4mm proud so this masterplan didn't actually work out. The battery itself, though, really impressed me. I built a little adaptor to convert the supplied DC line connector to the 817's 4/1.7mm socket, and spent many happy hours tuning the bands and making a few contacts. The battery has two flying leads: one for connecting to the charger and one to connect to the load.

Resigned to the fact that none of the currently available Li-Ion packs fits within the 817, I have now bought a bigger, 6800mAh unit. This capacity seems to be the most cost-effective and cost only £18. The cells are built into a sturdy plastic case which has a single DC in/out socket. It's 106x64x25mm and weighs 232g.

Both units have integral on/off switches and an on-board LED 'on' indicator (which must consume around don't forget to switch them off, after use!). All in all, handy, very portable, stand-alone power supplies. Both come with tiny mains-powered switch-mode chargers and, according to the ad on eBay for the larger unit, should only take around 3 hours to charge fully. I've been unable to validate this yet as I've not been in the shack to witness the 'fully charged' LED change colour.

Lithium-ion batteries require careful charging but the supplied chargers appear to be 'dumb'. However, there is some circuitry in the battery packs themselves to control the rate of charge and also to prevent over-discharge. Treat them with respect but also remember that these packs are everywhere: mobile phones, laptop computers, even hand-held transceivers.

So far, I'm very pleased with these units. If there's any updates - good or bad - I'll post them here. Meanwhile, I've used these to power up a little TV for sporadic-E watching and a wireless camera/receiver combination I use for checking out the wildlife overnight in the garden, as well as the rigs.