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Author Topic: Battery Pack Revisited  (Read 9081 times)
WB6BYU
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Posts: 14429




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« Reply #15 on: March 14, 2015, 08:45:03 AM »

Typically an SLA would take around 13.8V for float charge or a max
of 14.4V for quick charge.  The battery can be left forever on float,
though you only get about 80% capacity that way, but must be removed
from the higher voltage to prevent overcharging.

Maximum charging current depends on battery capacity and construction:
consult the manufacturer's data sheet.  You can charge it directly from a lighter
plug in the car, but the voltage and/or current may be excessive when the
engine is running.  (A series resistor or light bulb may make it more
practical, and perhaps a series diode - it can be done, but requires
attention.)

That's why it may be more convenient to find one of the automotive
backup battery packs that include a charger circuit, or get a proper 2- or
3-state charger and run it off an AC invertor.


SLA batteries are pretty safe as long as you don't short the terminals
or overcharge them.  I carry them with no more protection than perhaps
wrapping them in a hand towel to prevent short circuits.
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W8JX
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Posts: 8250




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« Reply #16 on: March 14, 2015, 10:07:52 AM »

You can charge it directly from a lighter plug in the car, but the voltage and/or current may be excessive when the engine is running.  (A series resistor or light bulb may make it more
practical, and perhaps a series diode - it can be done, but requires
attention.)

Chances of over current charging from lighter plug are about zero. No need for a resistor or light bulb. I doubt it would ever exceed even 14 volts under load. It is feed by a buss feed to powers car too and it already has some drop vs alternator output. Alternator output generally goes directly to battery and then buss is feed from there. I do agree that battery will likely never fully charge from light socket. It might make 80 to 90% after many hours.
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You can embrace new technology and change with it or cling tightly to old technology and fall further behind everyday....
KB1GMX
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Posts: 1067




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« Reply #17 on: March 14, 2015, 12:45:58 PM »

The ubiquitous 7Ah gell cell (new flavors are 8 or 9ah same size for a few dollars more)
is always a good choice.  That battery can easily run a 100W radio for a few minutes
at full bore or lower power for much longer.  But its about  5.8 pounds or so. 
FYI gell cells are a form of SLA (sealed led acid).

For tailgate and pick bench its a good choice. For power levels to about 20W.

If your really off the tailgate then why not the battery in the truck/car itself!

There are 12AH and 18AH SLA/gell cells for more power or greater time at power.
They run about 12 pounds weight and are common enough to be a low cost solution.

If you are carrying it further then there are Lithium based rechargeables.  In the same
7Ah size for about 120$ you get a higher AH (usually 9AH) and much lighter
 about 2.57pounds.  An example of this is Batteryspace  LF-LA12V9 at 130$
(fully protected, not raw cells).  An additional charger is low cost and a good idea.

Solar charging has value but if the panel is small its more weight than help.
the minimum size is slightly greater than what the receiver alone uses.
For example the FT817 I have that would suggest a 5-6W panel.  On transmit
to offset the load a 25W panel is enough.  however its not low weight for small
standard panels (20W under 80$)  and the "portable" foldable panels are
very expensive (over 300$).    Solar works but full sun to get rated power and
aimed at the sun.  I use it for FD ops, I grossly over size the panels for
power during weak sun and to hard charge the battery (with charge controller)
for night ops.  That works when you moving the gear maybe 100FT from the
truck/car.

In the end you need to know as before how much power you will use and for how
long. Also knowing how far you will carry or drag it is a deciding factor.

Allison
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AE5J
Member

Posts: 91




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« Reply #18 on: March 14, 2015, 01:31:54 PM »

Chances of over current charging from lighter plug are about zero. No need for a resistor or light bulb. I doubt it would ever exceed even 14 volts under load. It is feed by a buss feed to powers car too and it already has some drop vs alternator output. Alternator output generally goes directly to battery and then buss is feed from there. I do agree that battery will likely never fully charge from light socket. It might make 80 to 90% after many hours.

I think something was lost in the translation here.
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KB1GMX
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Posts: 1067




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« Reply #19 on: March 14, 2015, 02:52:02 PM »

I think what the story is...

You can't easily charge from a power plug (cigar lighter for old fuds) on a car.
You need to protect from excessive current and a fuse is safety and likely to
pop if the battery is way down compared to the car status.  Also the applied
voltage is only high enough with the engine running.  If you don't melt the
fuse you only charge to the idle voltage of the car battery (12.6V usually)
and that is a partial charge for the target battery.   In general a poor idea.

If you charging from a car the better way is use an inverter of say 200W and
a smart charger.  You will get better results, safer for the cars electrical system.

Allison
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W8JX
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Posts: 8250




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« Reply #20 on: March 14, 2015, 04:11:55 PM »

I think what the story is...

You can't easily charge from a power plug (cigar lighter for old fuds) on a car.
You need to protect from excessive current and a fuse is safety and likely to
pop if the battery is way down compared to the car status.  Also the applied
voltage is only high enough with the engine running.  If you don't melt the
fuse you only charge to the idle voltage of the car battery (12.6V usually)
and that is a partial charge for the target battery.   In general a poor idea.

If you charging from a car the better way is use an inverter of say 200W and
a smart charger.  You will get better results, safer for the cars electrical system.

Allison

Once again you will not get excessive current from that socket because voltage potentail difference is not enough to make it happen dah..  Some are kinda brain dead on this.   Another thing many equate a gel cell to a glass of water in that you get same amout from battery (like a water glass) no mater how fast you drain it. Such is not the case. If you are foolish enough to try to run a 100 watt rig off a single battery you will be lucky if you get 50 or 60% of stored energy before it is dead as rest will be lost to efficency and internal resistance. I hear many talk about using one while charging other but that is not best advice because you will recover more energy with them in parrallel feeding load as there will be less loss to efficency and rinternal resistance with each battery only seeing 1/2 of peak load and you will get notiably more total run time  and more stable voltage than using one at a time. But many are stuck on the glass of water thing and will drain them one at a time and cannot get past that. . 
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KB1GMX
Member

Posts: 1067




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« Reply #21 on: March 15, 2015, 09:56:41 AM »

Yes, you will.   Now you will make claims and the answer is
I tried it  with a  7Ah gell that was well down.  The 10A fuse
(in line with the gell) lasted maybe 50 milliseconds.  It might
have lasted less if the engine was running and instead of
the standing  12.7V trucks battery. The battery was sitting
at 11.5V (at least 80% DOD if not more).

Nominally if the battery isn't too far down I'd agree.  However
when the difference is more than 2V and the battery internal
resistances are low whats to limit current...  a few hundred
milliohms of wire, unsafe.

The problem is once the target battery is just a bit charged,
like you say not enough potential difference to do anything,
and it will only charge to the local voltage which is maybe 80%
given enough time (with the engine running you have a chance
for more).

Parallel feeding a load was not in the discussion from where I was.
Only charging the target battery.  Hence the suggestion of a low
power inverter and a smart charger.  Efficient, not,  but safe and will
work.  If you driving home after an outing that makes workable
situation.

As to running a radio at high power....  I've run my Eagle at full bore
for a few minutes (5 minutes SSB to be exact).  That's all I needed,
wanted or expected.  It did eat most of the 90WH in the battery and
I could see it at 12.2V and dropping during RX (2A load).  Good
idea, no, efficient no, I  needed time to  bridge to a different source. 
It did that.

Generally the battery in my mind should be at least 10X the RX power
needs (for the Eagle that's 20AH roughly, for my 817 thats 4.5aH).  That
only gets to a reasonable 1/10thC discharge rate for RX.   For a little
Rockmite that is more like 12V worth of Alkaline AAA cells.

The problem is still the how much weight does one what to deal with,
to run XXX radio at YYY power for how long.    For that we still need
to know:

RX/TX operating ratio.
Total time desired
Power needs of the radio for RX and TX(average).

What the usual question is that starts all this is reads like:

I want to run portable.  What battery should I get to run my KX3
from a picnic table and also the IC7200 for field day?

For that only one answer, the biggest thing you can carry times two.
Gotta go with the worst case.  The other no one even read.

Allison
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K7RBW
Member

Posts: 423




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« Reply #22 on: March 18, 2015, 05:51:13 PM »

I found this on Amazon: http://smile.amazon.com/RAVPower%C2%AE-23000mAh-Portable-External-Multi-Voltage/dp/B00HFMUBYG/ref=sr_1_6?s=wireless&ie=UTF8&qid=1426725964&sr=1-6&keywords=laptop+battery+pack

I've used it for about a month now and it's very light for a 23 AH battery. It's limited to 4.5A @ 12v. A 2-Amp load runs it down to 50% in 8-9 hours. I don't think it'd run a 100-w rig (@ 25 amps), but it would run a QRP rig for quite a while. It might run an FT-857/897 in battery mode. I haven't tried that, yet.

In any case, power-to-weight, it's a better deal than a SLA battery--I have a 35-AH SLA pack that weighs about 25 pounds. This pack weighs less than three.

Just another option.
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W4KYR
Member

Posts: 981




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« Reply #23 on: March 18, 2015, 06:20:54 PM »

I found this on Amazon: http://smile.amazon.com/RAVPower%C2%AE-23000mAh-Portable-External-Multi-Voltage/dp/B00HFMUBYG/ref=sr_1_6?s=wireless&ie=UTF8&qid=1426725964&sr=1-6&keywords=laptop+battery+pack

I've used it for about a month now and it's very light for a 23 AH battery. It's limited to 4.5A @ 12v. A 2-Amp load runs it down to 50% in 8-9 hours. I don't think it'd run a 100-w rig (@ 25 amps), but it would run a QRP rig for quite a while. It might run an FT-857/897 in battery mode. I haven't tried that, yet.

In any case, power-to-weight, it's a better deal than a SLA battery--I have a 35-AH SLA pack that weighs about 25 pounds. This pack weighs less than three.

Just another option.

Some rigs run OK at 12 volts, others need a little more 12.5, 13 or 13.8 volts. If the output could be boosted to 13.8 volts that would be perfect. But otherwise this looks like a good deal.

From the description:

" USB Smart Ports (3.5A MAX) to charge ALL devices at their max speed. Additional multi-voltage port (9V/12V/16V/19V/20V) for Asus, Acer & Surface tablets and more. Simultaneously charge 3 devices (4.5A max total output)."
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Still using Windows 98  ------------------ for Packet Radio.
KB1GMX
Member

Posts: 1067




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« Reply #24 on: March 20, 2015, 04:01:26 PM »

The 12V vs 13.8 problem is easily solved with one of the voltage converter boards.

Most Kit radios work fine at 11V.  Most radios that want 13.8 get unhappy below
12V (not all).

If the pack is current limited to 4-4.5A then it can't run most 100W radios as TX
no modulation is near 2.7-3.5 for most and even a few watts will go over that.
receive should be fine.    The K2, KX3 and FT817 would work fine on that.

Radios I know that seems to not mind 11.1V include FT817(all), FT857,
TenTec Triton (M540),, TenTec Eagle (M599) and I'm sure there are others.
However the 100w radios will not produce rated power with less than 13.8V
though they do work at lower power fine.


Allison
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W8JX
Member

Posts: 8250




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« Reply #25 on: March 20, 2015, 04:53:53 PM »

However the 100w radios will not produce rated power with less than 13.8V
though they do work at lower power fine.

I have not found this to be the case. It is usually well below 13 volts before power drops off and even then at 12v or less if you are still making 70 to 80 watts you will never hear difference down range. The need for 13.8 is over rated.
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You can embrace new technology and change with it or cling tightly to old technology and fall further behind everyday....
KB1GMX
Member

Posts: 1067




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« Reply #26 on: March 21, 2015, 10:05:56 AM »

W8JX,

Generally your right but there is more to "working" at reduced voltage.

Of the radios I've tried at 11V some just quit or the PLL/DDS system gets
unhappy.  A few have enough internal drop that under modulation they FM.
(756pro at 11.2V, Tentec 6n2 at 10.5V).  So operation needs to be checked
to find where the coffin corner is.

Others like my TS44SAT will do what looks like full power at 11.5, clipping
like mad SSB. Reduce power to about 85W cleans it up.  For communications
use 80 is as good as 100 and not a significant difference.  If your clipping due
to lack of voltage then it gets significant not for being heard but, because
being heard across the band is bad [especially at a FD site!].

The usual spec is 13.8V, 15%  that is roughly 11.8 to about 15.8 but full power
(W, IMD, harmonics) is spec'ed usually at 13.8 and not over the range.

The problem with that.... if your source is at 11.8 and at the radio end of the
power leads you hitting 11.4V on current peaks.  Then you have problems.
For a 5w radio that likely not to happen. For a 100W radio pay attention
as the voltage at the back of the radio may not be the battery voltage.

I do agree that 13.8V has a religious cult following that has little to no reality.
The average auto is 12.4 (sitting for hours parking) to 14.2 (buzzing down
the road) during the average day.   If your radio doesn't work at 12V then
fix something as I've found very few that don't and a few that didn't due to
minor internal power supply problems gone unnoticed.


Allison


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W8JX
Member

Posts: 8250




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« Reply #27 on: March 21, 2015, 05:53:48 PM »

I used a few TS 140's over last 20 years mobile and found they functioned well down to about 11 volts. But, I use a large electrolytic capacitor in parallel with rig power jacks which keeps voltage more stable than directly from a discharged battery. The cap is a great trick that is overlooked by just about everyone. My power did not drop below 100 watts until under 12 volts
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You can embrace new technology and change with it or cling tightly to old technology and fall further behind everyday....
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