Powering amateur radio from batteries

[clv101]

I have the Yaesu FT-857D radio and would like to be able to power it from batteries, like this guy is doing:
http://theapplebook.com/2012/02/portabl ... u-ft-857d/

So I need a battery and some means to charge it.

With a 20W transmit power the radio requires around 5 amps, around 1A RX. With say a 30% TX duty cycle a 7 Ah battery might be good for 3hrs (lower TX power would give more use). However, radio manual says:
Normal: 13.8 VDC ±15 % so below 11.7V it might shut down? How much of that 7 Ah capacity is available above 11.7V?

He's using a little 7Ah 12v SLA, kinda neat and I'd ideally have two so one could be charging while the other is in use. Something like this:
Ultramax NP7-12, 12V 7Ah for £10.
What sort of current can a battery like this deliver? 5A no problem?

Secondly the charger, more expensive than I thought. Here's what appears to be a reasonable charger:
Ultramax Battery Charger for Sealed lead Acid(SLA) Batteries. 12V 3Amp for £20. Should charge the 7 Ah in a couple of hours.

The other option, and perhaps more fun would be be a solar charging solution. A charge controller like this and a panel like this.

Any comments or recommendations on either option?

[adam2]

A 12 volt 7AH can certainly supply 5 amps, but not for very long, especialy if the voltage must remain above 11.7 volts.

I would expect a run time of less than 30 minutes, and a relatively short cycle life if discharged so rapidly.
Different brands of battery vary apreciably in their high rate discharge performance, those intended for small UPS units are usually best.

The battery charger linked to is probably too big for a battery of only 7AH.
It is a 3 stage charger that charges at a relatively high rate for a timmed period and then reverts to a lower float voltage.
During the high voltage charge, at a relatively high current, the battery will become warm, possibly too warm.
There is a small but real chance of thermal runaway, whereby the increasing battery temperature LOWERS the correct charging voltage, but since the battery charger does not know this, it continues fast charging and destroys the battery.
It might be fine, but I would think twice about unattended operation, especialy if the battery is warm from either hot weather or a recent high rate discharge.

I would select a 3 stage charger of no more than 1 amp output for a 7AH battery. This should also be cheaper.

Alternatively select a larger battery such as 17 AH, though these are heavy and expensive.
The 7 AH batteries are normally very cheap due to mass production, they are probably the most popular size.

Another option would be nicad emergency lighting batteries of 4AH, these are 1.2 volts per cell and one could therefore select 11 cells for 13.2 volts or 12 cells for 14.4 volts.
A 4AH nicad may give a longer run time than 7AH lead acid.

Either type gives enough current to start a fire if short circuited, a fuse is essiential.

[Catweazle]

A 4AH nicad may give a longer run time than 7AH lead acid.

From memory, a nicad will "give its all" - ie it will run until it's dead. You can't switch off and wait a while for it to recover. I think a lead acid battery can recover slightly, which might give you enough for an emergency use.

There are nicad battery packs available for radio controlled cars, with simple chargers, maybe one of those is suitable for mobile use - they're small and light - with a lead-acid type for home use.

[clv101]

There are nicad battery packs available for radio controlled cars, with simple chargers, maybe one of those is suitable for mobile use - they're small and light - with a lead-acid type for home use.

The 7.2V battery packs for radio controlled cars are fairly expensive, around £20 for a 4Ah NiMh. I'd need to pair them so we're talking close to £40 for 4Ah at 14V. This is quite a lot more expensive than the lead acids, but certainly a lot lighter.

I think my best bet would be a pair of 7Ah SLA and a charger, lower rated as suggested by Adam2. The 7Ah do seem to be the best value. Where can a buy a 10A DC circuit breaker?

[adam2]

I would be inclined to use a vehicle type in line fuse holder, these are very cheap and the trouble of replacing the fuse is of little consequence as it should very seldom blow.

Most circuit breakers need mounting in some form of box or enclosure which is a bit OTT for small scale equipment like this.

[RenewableCandy]

Doesn't this count as "preparations"? Especially since The Archdruid (report) has become a radio amateur for precisely this reason?

[clv101]

Doesn't this count as "preparations"? Especially since The Archdruid (report) has become a radio amateur for precisely this reason?

Yes, I guess it does! Moved.

[Tarrel]

Clv, I use 7Ah batteries exactly of the type you describe. If there are any radio fairs near you, pop along. You can usually pick them up dead cheap. I use three, wired in parallel, charged by a "Solar Briefcase" from Maplins. They were doing them on clearance a couple of years ago for £9.99, complete with regulator! This wouldn't be enough to use your radio for several hours each day (the briefcase is 15W IIRC), but it would be fine for occasional use or, in a SHTF situation, having the radio on Receive most of the time and just transmitting occasionally.

Whatever, try to avoid going down a Generator route. I've attended Field Days before where the club has tried to run the station from a genny. Terrible problems with interference.

[JavaScriptDonkey]

Security system PSUs come with battery back up and can feature line conditioning circuitry.
Same 7AH gel 12V type batteries.

Dantech are an esablished manufacturer and Norbains a well known supplier.

[clv101]

That looks like a rather useful product, I only see one place to actually buy it though and its £150!