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Author Topic: Battery questions  (Read 9738 times)
W3TTT
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Posts: 290




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« on: March 22, 2018, 09:38:00 AM »

I don't know if this is the right forum for my question.  I would like advice on batteries for portable and hiking use.  Hiking use means that I will carry it. Portable use means that I will carry it from the car. I have a ft-891 so I would like to get the full 100watts. I was thinking about those portable car starters.  Hoping that the group can provide advice.  Thanks.
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K5LXP
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« Reply #1 on: March 22, 2018, 10:51:37 AM »


Start with deciding what your typical operating profile will be - TX/RX duty cycle, and mode.  Then how long you'd like to do that for.  Find out what the lowest voltage is the radio will correctly operate.  Once you know those variables, you can calculate how many Ah you need.  From there you can decide on a size and chemistry.

Mark K5LXP
Albuquerque, NM

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KB1GMX
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Posts: 1658




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« Reply #2 on: March 22, 2018, 12:45:11 PM »

Seriously?

ITs a 100W radio, its going suck down about 240W {maybe more, or less}. 
That means it will want about 20 amps for voice peaks.  Both assertions
are assuming your running full power.

the manual confirms it:
Supply Voltage: 13.8VDC +/- 15%, negative ground
Current Consumption: Rx: 2.0 A (Signal Present) Tx: 23 A

Now with that established..  Most of the car starters are a 7 to 12AH gell cell
or an equivilent lithium type.   While they can supply the current for maybe
20-30 seconds needed to start a car they will not do it for minutes.  Also
the starter does not care if it sags to 10V while doing that.  The radio will!

You will need a bigger battery unless the total of your operating is limited to
"can you hear me now" once every 10 minutes.

If your more specific on what you want to try and do many here can help but
most of the car starter units barely run my 20W radio for any acceptable time.
Yes, I have two of the larger ones as they are handy for starting the lawn
tractor and other utility tasks!


Allison
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AA4PB
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Posts: 14731




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« Reply #3 on: March 22, 2018, 01:11:43 PM »

You also need to be aware of the type of battery for amateur radio use. Car batteries, for example, are designed to supply a large current for a short time to start the vehicle. They don't last very long in a use where they are continually deep discharged and then recharged as they would be in most portable 100W radio applications. You want a battery rated for "deep cycle" use.

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Bob  AA4PB
Garrisonville, VA
K0UA
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Posts: 2927




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« Reply #4 on: March 22, 2018, 05:20:12 PM »

I have an 891 I use portable.  I use a pack of 4 of the 7 amp hour gel cells.  BUT I don't run 100 watts.  I run 50 watts on SSB, and about 25 on CW.  Your signal is only down 3dB going from 100 watts to 50 on SSB.  BUT it makes a huge difference in current.  Or 6 dB down with 25 watts of CW.  If you can't get it down with 25 watts of CW, you need a better antenna.  Smiley  These would be my recommendations.  Turn her back a bit.  The 2 amps doesn't seem to be right on receive, it is more like 1.5 or so.   BUT you do have to deal with the transmitter bias current of about 4 amps when you go into transmit mode, before you ever speak a syllable.
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W3TTT
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« Reply #5 on: March 22, 2018, 05:23:48 PM »

The Yaesu FT-891 can draw 20 A at 100 watts.  In the shack I have a 20 A power supply.  But I would be happy to crank it down to 20 watts, which should be then drawing 4 A.  
I have two modes of operation in mind.

1.  Car portable.  I load all the equipment, battery, antenna etc. into the car and drive to the location - probably the park.
2.  Hiking - I carry all the equipment in my backpack.

Is this the type of battery K0UA?

Joe W3TTT
« Last Edit: March 22, 2018, 05:48:19 PM by W3TTT » Logged
N7EKU
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Posts: 1012




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« Reply #6 on: March 22, 2018, 08:44:03 PM »

Hi Joe,

Most hikers would go with a LiFePO4 battery.  These are much better for this use: they are 50-70% lighter so they pack more power per pound, and they last for many more cycles (1000's vs 100's).

Here's a good read about them:  http://www.cobox-ebikes.com/296/basic-understanding-of-lipo-li-ion-and-lifepo4.html

73,


Mark.
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Mark -- N7EKU/VE3
AE5X
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Posts: 1268




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« Reply #7 on: March 23, 2018, 05:48:53 AM »

The Yaesu FT-891 can draw 20 A at 100 watts.  In the shack I have a 20 A power supply.  But I would be happy to crank it down to 20 watts, which should be then drawing 4 A.  

That would be nice but it's not true. The FT-891 draws a bit over 8 amps with 20 watts out.

https://ve3ips.wordpress.com/2018/03/13/ft-891-ft-817-ft-818-ft-897d-and-icoms-current-drain-comparison-plus-a-kenwood/
« Last Edit: March 23, 2018, 05:51:03 AM by AE5X » Logged

K0UA
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Posts: 2927




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« Reply #8 on: March 23, 2018, 08:52:20 AM »

The Yaesu FT-891 can draw 20 A at 100 watts.  In the shack I have a 20 A power supply.  But I would be happy to crank it down to 20 watts, which should be then drawing 4 A.  
I have two modes of operation in mind.

1.  Car portable.  I load all the equipment, battery, antenna etc. into the car and drive to the location - probably the park.
2.  Hiking - I carry all the equipment in my backpack.

Is this the type of battery K0UA?

Joe W3TTT

Yes, that is the type of battery, but I use 4 of them.  Joe, keep in mind that the rig will draw 4 amps without putting out a single watt, due to the bias current to bias the finals.  This is a problem with using a 100 watt radio as a QRP rig, The finals are still 100 watt finals.  While you can crank the radio down to 5 watts, it will not be nearly as efficient as an actual 5 watt final that will draw milliamps for final bias current instead of  about 4 amps for bias current.  This is true with all 100 watt class radios not just the Yaesu.

But the 891 is a good rig for portable when cranked down some, but you just have to consider the extra current draw.
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W3TTT
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« Reply #9 on: March 25, 2018, 06:09:17 PM »

Yes, that is the type of battery, but I use 4 of them.  Joe, keep in mind that the rig will draw 4 amps without putting out a single watt, due to the bias current to bias the finals. 

My manual says that it draws 2 A with a signal but (and others have said) that it will draw 1 A on receive with no signal. 

On my envisioned SOTA mountain topping, I think that one hour of on air activity would be enough.  Any SOTA friends comment?  How long do you operate SOTA on site?
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WB6BYU
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Posts: 17864




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« Reply #10 on: March 25, 2018, 08:21:53 PM »

For car portable I look for batteries in the 30 - 40 Ah range.  K0UA's use of 4
of the 7 Ah batteries is a reasonable minimum.

You can't just assume that 1 battery will give you 1/4 the time of 4, however.  That's
because the internal resistance of the battery is important at high currents.  You
need to know the minimum operating voltage of the rig and make sure the voltage
doesn't drop below that on voice peaks where current is highest.  I generally
try not to draw more than 1/4 rating (so 2 amps from an 8 Ah gel cell) but will
stretch that a bit on SSB.  I'd expect 3 or 4 hours of operating from one of the
30 - 40 Ah batteries, depending on your operating style.

By contrast, I can run my K2 all of Field Day on one of them and have capacity
left over - that's the advantage of a rig designed for QRP and low current draw.


I've used the 35 Ah gel cells at 100 W for occasional contacts or checking into a
net, and float one across my power supply on Field Day so I can keep operating
when the generator quits.


The lithium batteries have a lower internal resistance, so a smaller capacity
battery may give more useful, but you would still want to watch the maximum
rated current on each battery.
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W8JX
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Posts: 13217




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« Reply #11 on: March 26, 2018, 07:46:53 AM »

My manual says that it draws 2 A with a signal but (and others have said) that it will draw 1 A on receive with no signal. 

Others are wrong. DSP rig have a higher standby power usage than analog rigs (reason new FT818 is still analog) Figure on 2 amps minimum draw.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
KB1GMX
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Posts: 1658




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« Reply #12 on: March 26, 2018, 09:21:07 AM »

Lets look back....

One case is for hiking...
Serious question, how far and home many days?  How much weight do you plan to or can carry?
Those set limits.  For example if you want to keep the pack under 40 pounds with water, food
and field gear other than radio how much is left for radio?

Radio is about 4.2 pounds, a battery for low power ops might be 5.5pounds for a 12V 7ah gell cell.
You want higher power so a 20ah LIFePo4 pack might be around 6 pounds. 
Not forgetting accessories and antenna so maybe 2 pounds.

Your up to 12-13 pounds in the pack just  for radio. and at about 25 watts that 20AH lithium will
get you about 10-5 hours of receive only and 1;10 ratio TX might get 5-6 hours to exhastion.
Of course if you want more power a 40ah lithium at about 12pounds will allow more or longer.
But then you hefting for radio alone 18-20 pounds total.


The other case is portable as in a short hike to maybe a picnic table.

How far can you carry a 55-60 pound 60ah deep discharge lead acid battery (AGM so its spill proof)?
That should be enough if the radio runs well at less than 12V (a fact or normal discharge) to
say 70% of capacity or about 8 hours.  Less if your contesting.  LIthium can cut that weight to
maybe 22 pounds, for a price!

One can argue the power consumption but unless the typicals are better by a factor of 2 its not
going to mean a great deal.  Also at some point the battery must be able to supply the require current at the
minimum voltage or the radio just quits/drops out.

NOTE most 100W radios when turned down toe 5W still draw large amounts of current as your biasing
transistors/fets designed for 100W operation.   The FT817 peaks at about 2A for 5W.  My Tentecs
(three different generations of 100W radios spanning 1977 through current) all draw more than 3.5A key
down and no modulation (zero power out) and reach about 5A at 5W.   So for low power and big radio
you still need a big battery to supply the high average and peak currents.

Note on RX draw...  My old analog Triton-340 eats about 250ma on rx.  MY 6n2 and Eagle both DSP IF want
closer to 2A on RX.   Most other DSP if radios all do about the same or worse on receive especially if they
have big displays and lots of lights.. 

size verses weight:
For battery weight use 1pound for every amp/hour@12V (approximation that seems to hold well for gell and AGM).
For lithium use about .32 pounds per amp/hour (LiFePo4 in the 3 to 50ah range) as an approximation.

As to lithium tech and max current most of the types out there are easily able to do the 20A even for very small
(in AH) cells but you can over heat them with seriously bad results.  Most batteries are protected by a board and that
will limit max current (read the specs).  They also must not be discharged below a certain voltage or the cell can be ruined.
The upside is for a heafty price its about 1/3rd the weight.  Again bottom line is Watt-Hours.

However in the end you talking useable Watt-Hours available and the radio is sucking down power at about 28-20W for RX
(DSP costs power) and near 240-250W on transmit and a typical 8ah gell has about 90-100 Watt-Hours.  If you want
operating hours you need lots of Watt-Hours.  Why?  Most batteries at high discharge rate go down faster.


Allison





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K0UA
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Posts: 2927




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« Reply #13 on: March 26, 2018, 12:37:51 PM »

My manual says that it draws 2 A with a signal but (and others have said) that it will draw 1 A on receive with no signal. 

Others are wrong. DSP rig have a higher standby power usage than analog rigs (reason new FT818 is still analog) Figure on 2 amps minimum draw.

NO YOU are Wrong.  I own one.  It is NOT 2 amps minimum. . I have see about 1.5 amps.  and my IC7300 which is a true SDR rig with a big "Fish Finder" display with waterfall only draws 1 amp.    You would think DSP rigs would draw more but the recent ones do not.  My 756pro3 which has a little bit of DSP, but still basically an analog rig draws 4 amps on receive.  Mostly due to the display and its back-lighting.
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K6LCS
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« Reply #14 on: March 31, 2018, 09:40:00 PM »

A good read is "Batteries in a Portable World" from the Cadex Corporation. Everything one needs to know about portable power ...

https://www.amazon.com/Batteries-Portable-World-Rechargeable-Non-Engineers/dp/0968211844/ref=sr_1_1?ie=UTF8&qid=1522557324&sr=8-1&keywords=batteries+in+a+portable+world

That's a link to the most current (pun intended) version. The five-year-old edition is a free read for Prime members.

There's a Kindle version for ten bucks, too.

I do not have the definitive answer for your needs. I suggest - as you already know - that you put a little effort into a better antenna, and turn that TX power down. Those two little items will dramatically increase run time of any portable power solution you make. I mean, hams are workin' the planet with their FT-817ND units and their whopping 5W TX power!
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Clint Bradford, K6LCS
http://www.spaceman.website
909-999-SATS
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