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Author Topic: How big a battery?  (Read 8684 times)
K5LXP
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« Reply #15 on: July 11, 2014, 11:21:21 AM »

Generally for Lead unless your recharging immediately I've seen cells fail on the fist few cycles.

I'm speaking for the amateur application of operating in the field and coming home to recharge.  I'm sure we could come up with a lot of use cases that deep discharges are a poor idea, but an afternoon of operating then recharging the next day, the battery will be fine.  Yuasa for one, does provide cyclic life spec's down to 100% DOD and it's more than 100 cycles.

http://www.yuasabatteries.com/pdfs/NP_7_12_DataSheet.pdf


Quote
most batteries in the last 10% show substantial voltage changes.

Right.  It works out that this is a self limiting process.  There aren't too many radios out there that will operate much below 11.5V much less 10.5V or lower, so you're almost guaranteed some degree of remaining capacity.  In the case of many Lithium batteries, the built in monitor circuits will cut off before damage can occur.  My point is that there's little advantage to quit using a battery at some arbitrary point.  Run it until either the radio or battery quits.


Quote
If you abuse a battery it could fail during the cycle you most want it for. 

Back to the typical amateur application - those levels of abuse don't happen here.  The operating conditions to cause damage to a battery aren't conducive to successful field operations.  You'd have to trying to hurt these batteries on purpose with something other than a radio for a load and a proper charger.


Quote
As to parallel batteries... poor option.  Most type want to be about the same age and use history or they will self discharged into each other.

Only if left that way unattended for long periods.  While actively discharging or discharging parallel batteries work fine together, even combinations of new/used and large/small.


Quote
that will just have the better charged one dumping energy in the lesser charged and that is not efficient process.

That doesn't happen.  You can't charge a battery with another one of the same voltage and chemistry no matter how disparate the state of charge.

You make a few other good points though about characterizing the radio and knowing the modes and currents that will be used.  How much margin one chooses above that to accommodate unanticipated situations or conditions is a separate debate.  My primary point is to dispel the myth that you can only discharge a battery to 50% or some other contrived number in the interest of battery life, because in this application it will most likely be age before cycle life is a factor.  You're paying for capacity and cycles, and carrying around a bigger/heavier battery than you have to only to take wasted life to the recycler.

My solution is to have half a dozen 7Ah gel cells on float, ready to go.  I can grab one and use it stand alone or use up to all six in parallel, and parallel that set to a wet cell battery (SLI or marine) if I need to.  Very adaptable and configurable for different scenarios.   

Mark K5LXP
Albuquerque, NM
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W8JX
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« Reply #16 on: July 11, 2014, 01:25:53 PM »

As to parallel batteries... poor option.  Most type want to be about the same age and use history or they will self discharged into each other.  L

Simply not true. I have paralleled auto batteries and gel cells for 40 years and i have never seen this. I only had a issue one time it that time period went a cell shorted in one and slowly drew other one down to 10.80 volts. Any this only happened because vehicle was not used foe several weeks. 
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KQ6Q
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« Reply #17 on: July 11, 2014, 09:11:47 PM »

If QRP CW is the operating mode, consider a smallish 4Ah Gel cell, and a compact folding solar panel - I have the 27W panel available through RadioShack online, with the regulator - during daylight, the panel runs the I-703 and tops off the battery - come sundown, I have an hour or two of operating time, depending on how much I transmit. The 50% transmit time in the original estimate is huge overkill if operating CW - unless running FM or or other  digital mode.... if you want to work all night, you'll need more batteries. Try something basic, go operating, if you need more batteries, buy some more. Don't over-analyze it!
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KB1GMX
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« Reply #18 on: July 12, 2014, 02:16:59 PM »

Quote
most batteries in the last 10% show substantial voltage changes.

Right.  It works out that this is a self limiting process.  There aren't too many radios out there that will operate much below 11.5V much less 10.5V or lower, so you're almost guaranteed some degree of remaining capacity.  In the case of many Lithium batteries, the built in monitor circuits will cut off before damage can occur.  My point is that there's little advantage to quit using a battery at some arbitrary point.  Run it until either the radio or battery quits.>

I did do that in the past and never got the expected life from the battery.  Also by actual experiment
(never mind theory) using one battery to charge another is inefficient, you always put more in than
you get back out for lead thats about 95% decreasing to about 50% as charge accumulates.  Multiple
batteries and switching to the next as the first goes down actually gives more operational hours. 
Also most of my radios run to at least 11.0V a few lower and the FT817 and a few of the HB radios
run to 9.  At 9V your seriously hurting a 12V gell (1.5V cell) as the usual cutoff for those is above
10.5V. 

In the end the trick s to be able to run without wondering if there enough left.  Obviously a huge
(relative to the transmitter power) battery works but its a pain to move.

Your right save for use to exhaustion means you have enough to run for the period suggested.
You always need more is my position and from real amateur use that has resulted in the past
a situation where the was just enough for RX only and the band had finally woken up.

Now I run parallel LION cells 20AH worth as its lighter per ah and weighs about that of  a
7ah gell and  holds up better.  The  CMB keeps it save but it can soak up a higher charge
as well (.5C is 10A).  I use that for long run times with an 817 as that while very portable
is power hungry.  The alternate was a 3s2p 5200mah lion pack and four volkswagon
solar panels (total 12.8W).  The battery CMB does both protection and charge
management for that pack. If there is light but not sun panels still provide some useful
charge.

Solar charging is a great way to extend run time if the desire is to keep the system
lighter.  For example a FT817 sucks down about 350ma (vhf everything on) in RX
at 12V and that's only 4.2W, two of those 3.2W Volkswagon panels are enough to
offset that and cheap too.   I used them as I had by luck come across four at a flea
for cheap.   There are an abundance of panels out there of many styles and depending
on budget they can be a useful aid to run times.

With a little care and plenty of measurements of the gear its easy to have enough power
for the desired period.   More often than not the power needed is understated for the transmitter
and of modest accuracy for the receiver.  The other is frequently field use runs less than the
expected duty cycle.


Allison


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W8JX
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« Reply #19 on: July 13, 2014, 07:26:03 AM »

You can drag out a few gel cells and even some solar panels which all adds to weight and mass to carry plus on cloudy days or in woods in shade solar panels are of little value. Simple take a 12 or 20 amp lithium battery that weighs less than a smaller gel cell and a rig and a small tuner and some wire and your ready to roll. With a 20 amp battery you could even bring a LED area light for night operation. You could likely get 24hrs of operation with a 817 and several days of just listening.
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W0VLL
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« Reply #20 on: July 14, 2014, 07:32:35 AM »

I bought this battery to get me started:

http://www.bioennopower.com/pages/12v-10ah-lifepo4-battery

It comes with powerpoles already installed and a charger.

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W8JX
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« Reply #21 on: July 14, 2014, 08:23:56 AM »

I bought this battery to get me started:

http://www.bioennopower.com/pages/12v-10ah-lifepo4-battery

It comes with powerpoles already installed and a charger.



Smart start for a portable setup.
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KF7DS
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Posts: 181




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« Reply #22 on: July 14, 2014, 11:07:00 PM »

That's a great battery. I use mine to power my IC 7100 at 40w CW and it trots along nicely for 3 hours. The chargers that come with them are very simple too.

Don KF7DS
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KB1GMX
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Posts: 714




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« Reply #23 on: July 17, 2014, 11:53:28 AM »

At 3.38 pound 10AH vs 4.8 pounds for the 8AH gell cell you have a better power source as well.
That is a  good deal with charger. 

If you use solar charging that LIPO can accept a far higher rate of charge then the lead ever could.

Good luck and enjoy,

Allison
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WB4TJH
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Posts: 189




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« Reply #24 on: July 21, 2014, 10:48:19 AM »

My portable operation is usually picnic table venues. I use a 7.5 or 12 amp hour gel cell  with my K2.
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W0VLL
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« Reply #25 on: July 21, 2014, 11:32:03 AM »

I did a practice session this weekend running off the battery. I discovered that my laptop is now the weak spot in my setup.

I only get about 3 hours of life out of the Macbook Air. It uses a lot of CPU decoding JT65 I guess.  Apple is very strict about licensing the magsafe power connector on the laptop, so little to no third party accessories are available for it.

I'm faced with the following decision:

1. Buy a new laptop
2. Try to find an external battery that has the magsafe connector
3. Run an inverter with the associated inefficiencies converting 12V - 120V - back to 12V.
4. Stop running digital modes and use the mic.
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KB1GMX
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« Reply #26 on: July 22, 2014, 03:30:01 PM »

There are external batteries or adaptors that have magsafe connector.

To get more run time try this.
  Turn of wifi, bluetooth, shutdown all aps not in use and lower screen brightness.

My solution for my Macbook was to take a spare 120V adaptor and cut the
cable off and make my own source.  The problem is the standard adapter is
16.5V so direct off 12V battery was less than effective (didn't work). I used a
variable input to any voltage switching converter module with 4A capability. 
I got lucky and found one that could be modded to deliver 16.5V.   Then I put it
in a well shielded and bypassed box to keep the switching noise in.

I might add it draws more than the radio on average.

I switched to a Eeepc 700 running linux as that wanted a lower voltage
and far less power (9.5V@3.1A max). it's old but runs FLdigi like a champ.
There are pads that run winders and those will run and charge off a 5V
backup like those used for phones.  Problem then is you need a USB to Radio
interface Adaptor.

Usually I use a pen, paper and forget the computer or use my Android tablet
and forget the digital modes.

Allison
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N8FNR
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Posts: 136




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« Reply #27 on: July 23, 2014, 10:13:53 AM »

I am planning on buying a Ten-Tec Argonaut VI and that rig draws 550ma on RX and 3 amps at 10 watts. Since I would want to use it sometimes in the field with a standalone battery how can I figure out what to battery to buy? I would be mainly using CW and PSK31. At most I would only use it a few hours a day and can’t imagine that it would be TXing more than 20% of that time.

Currently I am leaning towards one of these http://www.bioennopower.com/collections/12v-series-lifepo4-batteries/products/12v-15ah-lifepo4-battery but am not really sure which one to pick http://www.bioennopower.com/pages/comm-equipment-ham-radio . If anyone has other suggestions I am open to any ideas as I am not really sure how to pick a battery for this rig.

Zack
N8FNR
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N4MMI
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« Reply #28 on: July 23, 2014, 11:18:22 AM »

Zack:

I'm using the Bioennos too.  I have two of the 9Ah units that are setup like a SLAB (plastic case, flat lugs, sized like a 7/8Ah).  My theory is that two independent batteries are better than one big one.  One quits, you still have a second.  Forget the power meter at home?  Once one quits, you are only halfway done operating.  And if you are carrying your gear on your back, just take one 9Ah with you.  At 2.6 pounds, they are amazingly light compared to a similarly sized SLAB.  I have used mine with an IC-703 and am just starting to use it with a KX3.  Receive current drain on the KX3 is lower, but the IC-703 was close to your figures and operating SSB for a few hours here and there never made a big dent in one of these batteries.

I don't really get why folks buy the 10Ah Bioenno.  The 9Ah is much more ruggedly built and you pay a hefty weight price for the 1 extra amp hour (about 0.7 lbs).  The only signficant advantage to the 10 Ah is the increased burst amperage...30 amps, vs 18...neither of which I can imagine would be limiting with QRP gear.

http://www.bioennopower.com/products/12v-9ah-lifepo4-battery

/David
N4MMI
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G4AON
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Posts: 518




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« Reply #29 on: July 24, 2014, 02:13:00 AM »

I am planning on buying a Ten-Tec Argonaut VI and that rig draws 550ma on RX and 3 amps at 10 watts. Since I would want to use it sometimes in the field with a standalone battery how can I figure out what to battery to buy? I would be mainly using CW and PSK31. At most I would only use it a few hours a day and can’t imagine that it would be TXing more than 20% of that time.

Zack
N8FNR

Zack, based on my experience of operating portable on CW, which is around 40% duty cycle, over an 8 hour session you would probably use around 4.63 Ah based on your current drawn.

So for a lead acid battery, a 9 or 10 Ah size sounds about right. Perhaps slightly less if you use a lithium pack which can withstand deeper discharge.

73 Dave
http://www.qsl.net/g4aon/
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