Topics

Power supply


Michael Golden
 

I want to run my ubitx on a battery and I want it to run for 2 hours on digital modes.  No other item will be powered by this battery.  I’m assuming I can use a 12v lead acid battery.  How many Amp Hours do I need to accomplish this?

Thanks!


Bill Cromwell
 

Hi Michael,

I think people use a two and a half amp fuse with twelve volt batteries. So..less than three amp-hours each hour. If you use the entire three amps for each entire hour then two hours would be six amp-hours.  Part of each hour would use many fewer amps as the rig would be receiving (or not transmitting). Probably a four or five amp-hour battery would do the job. I have seven amp-hour batteries that run quite a while (weekend). My operations are NOT beacon or WSPR. You might survive two hours on smaaler battery. Try it snd see.

73,

Bill KU8H

On Sun, Sep 20, 2020, 13:46 Michael Golden <pldnmayor@...> wrote:
I want to run my ubitx on a battery and I want it to run for 2 hours on digital modes.  No other item will be powered by this battery.  I’m assuming I can use a 12v lead acid battery.  How many Amp Hours do I need to accomplish this?

Thanks!


Michael Golden
 

Hey bill, so I need to put 2.5 amp fuse inline between the battery and the ubitx?  If so I will look up how to do that.  I have a 12v 7amphour battery that we use for a kids toy that I also wanted to use on rare occasion with my radio


From: BITX20@groups.io <BITX20@groups.io> on behalf of Bill Cromwell <wrcromwell@...>
Sent: Sunday, September 20, 2020 2:52:43 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Power supply
 
Hi Michael,

I think people use a two and a half amp fuse with twelve volt batteries. So..less than three amp-hours each hour. If you use the entire three amps for each entire hour then two hours would be six amp-hours.  Part of each hour would use many fewer amps as the rig would be receiving (or not transmitting). Probably a four or five amp-hour battery would do the job. I have seven amp-hour batteries that run quite a while (weekend). My operations are NOT beacon or WSPR. You might survive two hours on smaaler battery. Try it snd see.

73,

Bill KU8H

On Sun, Sep 20, 2020, 13:46 Michael Golden <pldnmayor@...> wrote:
I want to run my ubitx on a battery and I want it to run for 2 hours on digital modes.  No other item will be powered by this battery.  I’m assuming I can use a 12v lead acid battery.  How many Amp Hours do I need to accomplish this?

Thanks!


Evan Hand
 

Michael,
There has been a lot of discussion in the past on whether a fuse is needed or not.  Some truly good engineers on this reflector say no.  I am an electrical engineer and do use the fuse.  My reasoning is it protects me from some of my "fat finger" mistakes (on at least two occasions).

There are few modes where you spend more than 50% of the time transmitting.  SSB may be one, however, SSB rarely uses the full 2.4 amps.  It would be safe to assume a 50% duty cycle, with the average being (1 + 2.5)/2 = 1.75 amps per hour.  That is half of the hour receiving and the other half transmitting.  Your 7 ampere-hour battery should last about 4 hours.  The worst case would be digital modes like FT8 and FT4.  I am excluding the beacon modes as those are transmitting almost all of the time.

I use car inline fuse holders like this:
https://smile.amazon.com/QLOUNI-line-Holder-Assortment-Puller/dp/B07G5JS535/ref=sr_1_15?dchild=1&keywords=mini+fuse+holder&qid=1600635459&sr=8-15
The 3 amp fuse would work for your purposes.  To install you cut the wire on the holder in half and splice it into the positive lead to the uBITX.

Hope this helps
73
Evan
AC9TU


vince adams
 

Group
Cut and splice? Would that not create a short? So, then I guess the short in the splice would need a fuse?
-

73, Vince KD7TWW


From: BITX20@groups.io <BITX20@groups.io> on behalf of Evan Hand via groups.io <elhandjr@...>
Sent: Sunday, September 20, 2020 3:01 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Power supply
 
Michael,
There has been a lot of discussion in the past on whether a fuse is needed or not.  Some truly good engineers on this reflector say no.  I am an electrical engineer and do use the fuse.  My reasoning is it protects me from some of my "fat finger" mistakes (on at least two occasions).

There are few modes where you spend more than 50% of the time transmitting.  SSB may be one, however, SSB rarely uses the full 2.4 amps.  It would be safe to assume a 50% duty cycle, with the average being (1 + 2.5)/2 = 1.75 amps per hour.  That is half of the hour receiving and the other half transmitting.  Your 7 ampere-hour battery should last about 4 hours.  The worst case would be digital modes like FT8 and FT4.  I am excluding the beacon modes as those are transmitting almost all of the time.

I use car inline fuse holders like this:
https://smile.amazon.com/QLOUNI-line-Holder-Assortment-Puller/dp/B07G5JS535/ref=sr_1_15?dchild=1&keywords=mini+fuse+holder&qid=1600635459&sr=8-15
The 3 amp fuse would work for your purposes.  To install you cut the wire on the holder in half and splice it into the positive lead to the uBITX.

Hope this helps
73
Evan
AC9TU


Reed N
 

On Sun, Sep 20, 2020 at 10:46 AM, Michael Golden wrote:
I want to run my ubitx on a battery and I want it to run for 2 hours on digital modes

Hi Michael,

Which uBiTX version do you have, which mods have you added (if any), what digital mode will you be using, and on which band(s)? All of these could affect your runtime. The best way to ensure you have a full 2 hours of operation is to measure your rig's power consumption when doing the exact sort of operations you would want to perform during battery operation, then buy a battery to match. The easiest empirical way to figure out your capacity need is to measure the current of your rig, as you've built it, during both RX and TX of the digital mode on the band(s) you'll be using. You could monitor the current continuously over a few minutes of use, and extrapolate, however you'd probably be fine measuring RX and TX once (for each band and mode), and then combining them linearly with time and duty cycle.

For instance, suppose you're hoping to use BPSK-31, and expect to listen 75% of the time, and transmit 25% of the time. Then you'd measure your rig's current while receiving, and transmitting. To get a rough estimate of what capacity we might expect a uBiTX to need, let's say you read 0.2A at 13.4V during RX, and 2.1A at 12.9V during TX (numbers worst-case ball-parked from https://groups.io/g/BITX20/message/40043 and https://groups.io/g/BITX20/message/41108 since I haven't actually measured my v6 - I expect the v6 screen consumes more power than these numbers show, and a Nextion screen possibly even more than that). We calculate 0.75*0.2A + 0.25*2.1A = 0.675A as our average power requirement, so to get one hour of operation, we'd need 0.675Ah of battery capacity. For two hours, we'd need twice this much, or 1.35Ah. If you also wanted to operate FT8, which has a 50% duty cycle if continuously operated, then calculation would become 0.5*0.2A + 0.5*2.1A = 1.15A, so you'd need 1.15Ah for one hour, or 2.3Ah for two hours.

While the measurements and calculations above will get you the *minimum* required capacity, you should probably assume some efficiency losses, and that you may not have a fully charged battery at the start, since batteries self-discharge over time. It's also not good to fully discharge lead acid batteries, and the rough number I've heard to avoid damage is to aim for a discharge of no more than 50% of the lead-acid's total capacity (https://www.spiritenergy.co.uk/kb-batteries-understanding-batteries and https://simpliphipower.com/company/news/blog/know-your-battery-specs-nameplate-capacity-10-kwh-vs-usable-capacity-7-kwh/ both state this value). If we start with our 2.3Ah from the example above, we can round up to 2.5Ah to give ourselves a little margin (and make the math easier), and then account for the lead-acid max safe 50% discharge by choosing a battery with at least 2.5Ah/(0.5) = 5Ah of total capacity. If you were to choose, say, a LiPo battery with an 80% max safe discharge instead, then for the same 2.5Ah margin, you'd only need 2.5Ah/(0.8) = 3.125Ah of total capacity.


Reed