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Author Topic: Power Consumption Calculatiosn (fork from Battery Maintainer thread)  (Read 135 times)

KD9FRQ

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It was mentioned in the Battery Maintainer thread that one needs to know the power consumption value to help know how much is consumed to then determine how big a maintainer is need to replenish.

So, how does one actually calculate the use?  My rig FT-897 sits idle at .5 amp But the manual does not stated .5 per second, minute or hour.  My FT-450 outputs 30w for 13 seconds (should 30% of 22amps or 6.6) when sending FT-8 and 1.5 amps idle with signal coming in. So did I just use  8.1 amps?

If I used 8.1 amp, how much is left in my 100AH battery? only 91.9AH?  That means digital mode will not last very long in the field.
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K5LXP

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #1 on: August 01, 2020, 06:57:57 AM »

My rig FT-897 sits idle at .5 amp But the manual does not stated .5 per second, minute or hour.

"Forever".  .5A as long as the radio is turned on.  So if you were basing consumption in terms of hours, this would be .5Ah.

Quote
My FT-450 outputs 30w for 13 seconds (should 30% of 22amps or 6.6) when sending FT-8 and 1.5 amps idle with signal coming in. So did I just use  8.1 amps?

If you're trying to determine your consumption in amp hours, you need know your RX current, TX current, TX duty cycle, and TX time.

13 seconds of transmit in a one hour period would hardly move the needle in terms of Ah used.  If it's 13 seconds every minute for an hour, that would be fairly significant.  Even if it's just an estimate, you need to have some idea of how much transmitting per hour and what mode to get a good idea of overall power consumption.

I use a spreadsheet that I can input RX current, TX time, and TX mode.  This gives you required Ah which you can then apply to a given battery size and performance characteristics, and can predict with pretty good confidence how much operating time you can expect.

One more factor to consider is some radios don't operate over the full range of voltage a lead acid battery provides.  Radios are usually spec'd for 13.8V +/- 15%, so on the low side you're only about 50% into the power delivery of a battery.  Some radios offer more voltage margin than others and sometimes you can extend operating by reducing transmit power, so all those variables need to be known if you want to extend your operating time beyond the published spec.

Mark K5LXP
Albuquerque, NM
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N8AUC

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #2 on: August 01, 2020, 08:41:58 AM »

Mark is right. Capacity is measured in Amp-HOURS.
How much current you draw matters, but how long you draw that current, and over what duty cycle also matters.

How many amp hours did you use? That depends.
First off, the amp hour rating of a deep cycle battery (Lead acid chemistry is assumed here) is usually determined by supplying a constant 0.05C load current for 20 hours. So if you have a 20 Amp hour battery, that means it should deliver a 1 amp continuous load for 20 hours before it is depleted.

Note that the term "depleted" is a very relative term. From the battery manufacturers standpoint, depleted is when you have reached the maximum stated depth of discharge, which usually occurs at a voltage of 10.5 volts for a 12 volt battery (Lead acid chemistry). But your radio wants to see 13.8V +/- 15%, so for you the battery is depleted when your rig will no longer operate properly, which would be at a voltage of 11.7 volts.

But you're not going to draw a constant current. Your current draw will vary between transmit and receive.

So, how many amp hours DID you use?

Let's take your FT-450 as an example. Say it draws 6.6 amps on transmit (at 30w output), and 1.5 amps on receive.
You transmit for 13 seconds, and then listen until it's time to transmit again. For the sake of this example, let's say you transmit once every 5 minutes, or 12 times per hour.

So over the course of an hour, you'll transmit for 13 x 12 or 156 seconds, and you'll receive for the the remaining time, which would be 3600-156 or 3444 seconds.

156 seconds is 4.3% of an hour, so you're receiving for 95.7% of an hour.

6.6 amps * 4.3% * 1 hour = 0.28 amp hours on transmit, and 1.5 amps * 95.7% * 1 hour = 1.45 amp hours on receive.
So in this example you would have consumed 0.28 + 1.45 = 1.73 amp hours during that 1 hour time period.

And you can keep doing that, until the battery voltage drops to 11.7 volts, however long that takes. You will have to discover that empirically (trial and error).

If you transmit more and receive less then your amp hour consumption will rise, and your battery will deplete faster.
If you transmit less and receive more than your amp hour consumption will decrease, and your battery will deplete more slowly.

Hope this helps, and makes sense.

73 de N8AUC
Eric

« Last Edit: August 01, 2020, 09:02:09 AM by N8AUC »
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KD9FRQ

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #3 on: August 01, 2020, 12:00:53 PM »

THANK YOU!!!

That is the information I needed. A piece of the puzzle has been found for me.

I was thinking I needed a huge bank of batteries.  My two 55Ah for one set
and two 100Ah for another will work nicely.
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K0UA

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #4 on: August 01, 2020, 03:25:11 PM »

THANK YOU!!!

That is the information I needed. A piece of the puzzle has been found for me.

I was thinking I needed a huge bank of batteries.  My two 55Ah for one set
and two 100Ah for another will work nicely.

One more little "gotcha".  100 watt rigs are not efficient running 30 watts like a rig that was designed to have a maximum of 30 watts out would be.  The reason is because of bias current for the final amplifiers. Most 100 watt rigs will run about 4 amps of bias current the instant they are keyed, WITHOUT any FT8 audio even applied. Check it out on your rig. Run the WSJT-x audio all the way down, and observe the current, you will see what I am talking about.  You might do a mental calculation and say. OK, 30 watts  would be less that 1/3 of the 22 amperes so maybe 6 amperes.  Bet it is more, because of the bias current.  So even in SSB mode with no audio, and NO power output, you are drawing significant current.  This is why a 100 watt class radio turned down to 5 watts won't last near as long on a given battery as a 5 watt rig running full bore 5 watts out. Note even half as long.
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73  James K0UA

N8AUC

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #5 on: August 01, 2020, 05:35:31 PM »

THANK YOU!!!

That is the information I needed. A piece of the puzzle has been found for me.

I was thinking I needed a huge bank of batteries.  My two 55Ah for one set
and two 100Ah for another will work nicely.

One more little "gotcha".  100 watt rigs are not efficient running 30 watts like a rig that was designed to have a maximum of 30 watts out would be.  The reason is because of bias current for the final amplifiers. Most 100 watt rigs will run about 4 amps of bias current the instant they are keyed, WITHOUT any FT8 audio even applied. Check it out on your rig. Run the WSJT-x audio all the way down, and observe the current, you will see what I am talking about.  You might do a mental calculation and say. OK, 30 watts  would be less that 1/3 of the 22 amperes so maybe 6 amperes.  Bet it is more, because of the bias current.  So even in SSB mode with no audio, and NO power output, you are drawing significant current.  This is why a 100 watt class radio turned down to 5 watts won't last near as long on a given battery as a 5 watt rig running full bore 5 watts out. Note even half as long.

James,
In many cases what you say is absolutely true.
I know that for my FT-857D, when I turn the power down the measured current consumption is:
5 watts out, 2 amps
20 watts out, 4 amps
30 watts out, 5.5 amps.

Interestingly, my FT-817 also draws 2 amps for 5 watts output.

My measurements were taken in CW mode.

73 de N8AUC
Eric
« Last Edit: August 01, 2020, 05:51:43 PM by N8AUC »
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N8AUC

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #6 on: August 01, 2020, 05:39:15 PM »

THANK YOU!!!

That is the information I needed. A piece of the puzzle has been found for me.

I was thinking I needed a huge bank of batteries.  My two 55Ah for one set
and two 100Ah for another will work nicely.

I'd say you're in pretty good shape.
Add some solar panels and a charge controller to keep them charged off grid. and you can stay on the air for a very long time without any commercial power.

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K5LXP

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Re: Power Consumption Calculatiosn (fork from Battery Maintainer thread)
« Reply #7 on: August 02, 2020, 06:20:44 AM »

One of these inexpensive inline power-current-wattmeters is a very handy accessory to have to monitor your power status at the operating position.



Mark K5LXP
Albuquerque, NM
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