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Author Topic: Portable battery power  (Read 15637 times)
ON5RKN
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Posts: 6




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« on: September 30, 2013, 09:02:16 AM »

I have 2 agm batteries, (enersys Powersafe 12V92F)

In the future I want to use these batteries as power supply for emergency purposes,
or for all kind of nice tests in the field.

Now is my question what is the best thing to do:
a setup with one single battery and a power inverter from 12V tot 220V in combination with my 13.8V power supply,
or the 2 batteries in series using a DC/DC converter 24V to13.8V?

I found a lot of ideas on the internet and in these forum so that i don't know what's realy the best is to do. 
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WX7G
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« Reply #1 on: September 30, 2013, 09:05:04 AM »

Both ideas introduce conversion losses of 20 to 40 percent. The most efficient is to parallel the two batteries and power the radios directly.
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KG4RUL
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« Reply #2 on: September 30, 2013, 09:07:23 AM »

I have 2 agm batteries, (enersys Powersafe 12V92F)

In the future I want to use these batteries as power supply for emergency purposes,
or for all kind of nice tests in the field.

Now is my question what is the best thing to do:
a setup with one single battery and a power inverter from 12V tot 220V in combination with my 13.8V power supply,

-- You lose energy to heat twice in this setup: the inverter; the power supply - In addition, inverters can be tremendous sources of RFI

or the 2 batteries in series using a DC/DC converter 24V to13.8V?

-- Again losing energy to heat: the converter

I found a lot of ideas on the internet and in these forum so that i don't know what's realy the best is to do. 

-- Why not just use the batteries directly as sources of 12VDC power?
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ON5RKN
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« Reply #3 on: September 30, 2013, 11:00:38 AM »

is 12V enough? I thought that some equipment not properly worked when they do not have 13.8v
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W8JX
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Posts: 6470




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« Reply #4 on: September 30, 2013, 02:25:48 PM »

All equipment will work on 12 volts though some may not develop full output.
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W6EM
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« Reply #5 on: September 30, 2013, 07:47:44 PM »

MFJ makes a 20A-class voltage booster, the MFJ-4416, that is designed as a boost regulator to raise battery output to 13.8VDC to get around the problem you describe.  They claim 90% efficiency in doing so.

Although not inexpensive, they will provide a regulated output voltage as the battery terminal voltage diminishes.

Also, I wouldn't parallel them for the simple reason that you could run one down, switch it out and recharge it while continuing to operate from the other.
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KF7VXA
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« Reply #6 on: September 30, 2013, 08:53:44 PM »

The MFJ voltage boosters do work quite well. There is a lower priced one made by someone else, stay away from it, kinda noisy.
They are all about 90% efficient, so there is some loss, but they do allow extra run time because once a battery gets below 12 volts, radio problems do start to pop up. The MFJ does have a crowbar also.
I run my batteries down to 10.5 to 11 volts with the booster and like the extra time. It of course does take longer to recharge the batteries, so having about 3 or 4 batteries is a plus.
I also hook up about 125 watts worth of PV power to the batteries in the daytime when transmitting, it will increase the use time quite a bit unless you lean on the talk button a whole lot.

73's, John
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W9FIB
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Posts: 901




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« Reply #7 on: October 01, 2013, 03:56:30 AM »

I have tested several different Yaesu and Icom rigs on batteries. They all worked down to a voltage of between 10.4V and 11.1V. Yes the output does drop some, but they still work.

The "claim" by MFJ of 90% efficiency is with fully charged batteries. BUT as your supply voltage drops, so does efficiency. The reason is simple. The lower the input voltage, more current is needed to continue to maintain your output voltage.

If you are receiving most of the time, and you don't need every single watt out possible, you will have far longer use of the batteries without the MFJ regulator. At 11 volts, my measured efficiency was down to 61%. That is 39 percent of your precious power being converted to heat when you can least afford it to be wasted.

And really, on a 100 watt rig, how often would the loss of 20 watts or so really make a difference? Your still way above QRP operation. But then turning your rigs output power down also makes the batteries last longer. Many times in QSO's on 75M I would turn my rig output down to 25 watts or so. Still was heard just fine, but my s units did drop off on the other end. But if you maintain the connection fully readable, your simply wasting those "extra" watts anyway.

Smart operation on battery extends your battery life far more then anything else ever will. And create much less heat which is simply wasted power as a plus.
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W8JX
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« Reply #8 on: October 01, 2013, 05:17:18 AM »


Also, I wouldn't parallel them for the simple reason that you could run one down, switch it out and recharge it while continuing to operate from the other.

Not best advise. The reason is running both batteries in parallel will give more than 2x run time because battery efficiency improves as discharge rate is decreased. It will also provide a more stable voltage too.
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W6EM
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Posts: 882




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« Reply #9 on: October 01, 2013, 05:27:42 AM »


Also, I wouldn't parallel them for the simple reason that you could run one down, switch it out and recharge it while continuing to operate from the other.

Not best advise. The reason is running both batteries in parallel will give more than 2x run time because battery efficiency improves as discharge rate is decreased. It will also provide a more stable voltage too.

Let me qualify my advice a bit more.  Just when does one stop operating to recharge both batteries at the same time?  Most chargers can and do put out almost 15VDC.  Very dangerous to try to charge and continue operating.  Even if the batteries hold the voltage down for a while, high charger voltage can cook many radios.

On the other hand, if you figure out how much time you'll have with the two in parallel and plan on shutting down for 4 to 5 hours or so when both are charging, then no big deal.
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W8JX
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« Reply #10 on: October 07, 2013, 10:58:59 AM »


Also, I wouldn't parallel them for the simple reason that you could run one down, switch it out and recharge it while continuing to operate from the other.

Not best advise. The reason is running both batteries in parallel will give more than 2x run time because battery efficiency improves as discharge rate is decreased. It will also provide a more stable voltage too.

Let me qualify my advice a bit more.  Just when does one stop operating to recharge both batteries at the same time?  Most chargers can and do put out almost 15VDC.  Very dangerous to try to charge and continue operating.  Even if the batteries hold the voltage down for a while, high charger voltage can cook many radios.

On the other hand, if you figure out how much time you'll have with the two in parallel and plan on shutting down for 4 to 5 hours or so when both are charging, then no big deal.

Most chargers are smart now and can limit charge rate and voltage. There is no danger charging battery with a smart charger while using it and you will spend less time charging with to in parallel because discharge and charging efficiency will improve too. One has to loose the "glass of water" mentality when dealing with batteries because while a glass of water can be emptied and filled at any rate to capacity a battery cannot be. The slower you discharge it the more energy you recover. Battery service life will be better too.
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W6EM
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Posts: 882




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« Reply #11 on: October 08, 2013, 05:54:12 PM »


Most chargers are smart now and can limit charge rate and voltage. There is no danger charging battery with a smart charger while using it and you will spend less time charging with to in parallel because discharge and charging efficiency will improve too.

Not usually true for lead acid cell chargers a typical ham might buy.  But, if someone invests in a UC3906 based charger (A&A Engineering), even those will source constant current at very elevated voltage if the cell voltage is low enough to begin with until it builds up and changes states.  A bumped alligator clip or separated power pole could momentarily open circuit the battery and subject equipment to 15V or higher under the right circumstances.

Some Yaesu radios, for instance,  have TVSS diodes in them and will short out at just over 15V.  Not a pretty sight.

We also should lose that Nicad-HT drop-in charger mentality as well. 




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W8JX
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Posts: 6470




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« Reply #12 on: October 09, 2013, 04:31:34 AM »


Most chargers are smart now and can limit charge rate and voltage. There is no danger charging battery with a smart charger while using it and you will spend less time charging with to in parallel because discharge and charging efficiency will improve too.

Not usually true for lead acid cell chargers a typical ham might buy.  But, if someone invests in a UC3906 based charger (A&A Engineering), even those will source constant current at very elevated voltage if the cell voltage is low enough to begin with until it builds up and changes states.  A bumped alligator clip or separated power pole could momentarily open circuit the battery and subject equipment to 15V or higher under the right circumstances.

Some Yaesu radios, for instance,  have TVSS diodes in them and will short out at just over 15V.  Not a pretty sight.

We also should lose that Nicad-HT drop-in charger mentality as well. 


Given that a cars electrical system can easily exceed 15 volts for a few minutes on a cold day after start if rigs were that sensitive there would be a lot more blown rigs.
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KC0UKR
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Posts: 38




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« Reply #13 on: October 09, 2013, 05:58:44 AM »

Jut use a marine 2 battery switch and be able to choose either battery or both or a sure shut-off by flipping the switch.
These are very high current heavy duty switches designed exactly to make using 2 identical batteries work together in any combination.
I use them all the time and they just work.

Ed
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W6EM
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Posts: 882




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« Reply #14 on: October 09, 2013, 07:41:37 AM »


Most chargers are smart now and can limit charge rate and voltage. There is no danger charging battery with a smart charger while using it and you will spend less time charging with to in parallel because discharge and charging efficiency will improve too.

Not usually true for lead acid cell chargers a typical ham might buy.  But, if someone invests in a UC3906 based charger (A&A Engineering), even those will source constant current at very elevated voltage if the cell voltage is low enough to begin with until it builds up and changes states.  A bumped alligator clip or separated power pole could momentarily open circuit the battery and subject equipment to 15V or higher under the right circumstances.

Some Yaesu radios, for instance,  have TVSS diodes in them and will short out at just over 15V.  Not a pretty sight.

We also should lose that Nicad-HT drop-in charger mentality as well. 


Given that a cars electrical system can easily exceed 15 volts for a few minutes on a cold day after start if rigs were that sensitive there would be a lot more blown rigs.
Caveat Emptor.
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