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Power consumption of rigs

My IC706mk2 on a battery takes 4 amps when the PTT is pressed in ssb mode without speaking into the mike, can anybody confirm this is normal, have I got a fault? The 817 I borrowed takes 490ma in the same condition. No wonder I need a power station for the 706 on a hilltop! An old IC202 takes only 80ma on rx. Sorry if this has been discussed before somewhere just getting QRV again.

In reply to GM4GUF:

Sounds a lot for a no audio condition. You don’t say what it takes on RX though?


In reply to MM0FMF: Yes does seem alot, 706 takes 1.1amps on receive ssb.

In reply to GM4GUF:

Well if it’s 1.1A on RX I’d expect somewhere around 2.5-3A(max) for TX. There’s about as much circuitry powered on TX as RX apart from a PA/driver bias currents and possibly the odd relay or two.

Really you need info from someone who has one.


In reply to GM4GUF:
Hi Robert
My old IC-706 takes the same amps like yours. However, on 5 watts cw with a 9 Ah battery I can be qrv for more than two hours, maybe three (did not try).
I have so far no intention to buy an expensive qrp rig just for SOTA. It can be nice to have the possibility to use higher power in bad condx, at least to get enough qso’s for a valid summit.

In reply to GM4GUF:

I too have an IC 706 MkII but found it heavy on he juice from hill tops. Compared to the similarly specified FT-857D it is a guzzler(you can check the official figures on the manufacturers web sites). I believe the problem lies in the Icom’s DSP circuitry as the old 706 is a tad better. The 857 will also work the battery down to a much lower voltage (probably because it is almost an 817, which runs at 9.6v on internal batteries but with a bigger OP) than the 706 which goes in to a sort of self oscillation at about 11.5v. I have an FT-817 and decided after a few summits where I was sure I was going to fail qualify to make sure I had the power if I needed it. After several trips with the Icom I decided it was too heavy and too hungry and it was sent to do service on 10/6/2 ssb in the shack but it is still a great rig and I will not part with it. I now have two 857s one of which died on my recent trip to South Scotland and the other which is destined for installation in my vehicle.

73 Steve GW7AAV

In reply to GM4GUF:
I dont think its a fault Robert.
My IC-706 (first edition) takes abt. 1.8A on receive only, and takes 5 A on low output (5 watt). This consumption is going up to 7.5A at 10 watt and 10.5A at 25 watt. This figures are measured during a lighthouse activation with a half wave longwire as antenna. In the ICOM manual it is: 20A at full power. By pressing the PTT switch a fan is starting and maybe some more? By pressing my PTT the figure is nearly the same as yours, 3A, here at home, power supply is 13.8 volts.
Thats the reason i use only CW and the power source is a car battery at my SOTA and lighthouse activations.

73, Age - pa0xaw

In reply to PA0XAW:
Hello everybody

did you try the new battery technologies, currently extremely popular in electric plane models ? Two of them seem very promissing : lithium polymer and lithium iron phosphate.

Basically, we could have 4 Ah in a 500g very small pack. So for 3 kg we can feed a regular rig at full power during a SOTA day.

Another key feature is the extremely low impedance: battery voltage is almost constant when sinking maximum current.

I have spend time reading about that, but couldn’t make any trial. If someone can provide field information…

73 from Alain

In reply to F6DYA:
Hi Alain
I also fly model aircraft / helicopters and use Li-Po cells. They are very good, light weight and pack a big punch. I have found with current draws around 20A that the maximum life is around 50 charges (some do more, the Chinese cheap cells less). However, be very careful when charging as there have been reports in the model press about cells exploding, not the gentle venting as in Nicad, but a full blown mushroom cloud and a big hole in the desk. To this end, only use a “proper” Li-po charger and cell balancer and you will be fine. There are some examples of li-po cells been pushed to the limits on youtube, very spectacular, but also very dangerous. Other things to note, the batteries have a “C” rate, this is the maximum current you can draw from them, so a 1000MAh cell with a 10C rate can supply 10A, a 20C rate can supply 20A etc. The “C” rate also gives the maximum charge current, in the example above, a maximum charge of 1A for one hour. The charger should sort this out for you. When in use, the cells can go unstable and into self destruct if discharged beyond their specified limit, and of course will then need to be disposed of. In the model world we have a device known as an ESC (electronic speed controller) that can have the safe lower limit for discharge set so that it cuts the motor and warns the user that they are approaching the critical discharge limit thus preventing damage.
As a final note, for emergency use the cheap Chinese cells are ok, but can vent for no reason if pushed, and don’t last as long as a reputable=more expensive cell. Try a google search for “giant cod”, or “BRC hobbies”, two suppliers in the UK I have used who give loads of advice and are very competitive on price.

In summary, great if used correctly, otherwise beware, they pack a nasty bite.

Hope this helps


In reply to F6DYA:

I have been using 5000mah LIPO packs to power 100w radios (ft857d and IC7000)for a while now, the weight saving over an equivalent SLAB is good.

The only real problem is that the LIPO 3 cell (11.1v nominal) pack voltage is to low and the 4 cell (14.8v nominal) pack voltage is to high. The fully charged voltage for the 4 cell pack is approx 16.8v and most radios have a maximum specified voltage of 16v or less.

The way I got around this was to put some rectifier diodes in series with a 4 cell pack and drop the voltage down to a more acceptable level. When the voltage drops enough then I remove the diodes with a jumper lead, this is a manual process.

A DC-DC switching circuit might be a better option than the diodes.

When you buy LIPO packs take care to buy them with a high C rating, they are normally specified as something like 5000mah 25C, the 25C means it can supply 25 x 5000mah = 125 Amps current. From experience I would not buy anything less than a 5000mah 20C pack to power a 100w radio.

As an operating example I operated from F/AB-257 using a mixture of 100w, 50w and 25w ssb for two hours with a 5000mah 25c lipo pack and made 80 contacts approx. At full output it lasts for an hour approx.

The IC7000 runs at full output (110w approx) with the LIPO pack and at around 80w with a fully charged SLAB. The ft857d is not so fussy, but still puts out more power with the higher voltage supply.

Another way of getting around the voltage problem is to use the pack to drive an external amplifier directly at the higher voltage. I have done this with an ft817 and a home brew amp running at the full 16 volts. This increased the power output from about 60w at 12 volts to 100w+. There is nothing stopping you running external amps with much higher voltage packs.

You do have to be carefull that the individual cells of a LIPO pack dont drop below 3v. Some people do this by checking the overall voltage of the pack, but this is not really good enough, as in practice one cell will drop faster than the others and the overall voltage will not indicate that a cell has fallen below 3v. The best method is to monitor the voltage of the cells via the balance charge plug on the LIPO pack, you can buy small LED monitors that plug into the port and flash the voltage of each cell in turn and also the combined voltage.

The ft817 work really well with 3 cell 11.1v LIPO packs.

Lithium Ion Nanophosphate is worth looking at as the voltage operating range is more compatible with 13.8v equipment.


Nigel. G6SFP.