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Author Topic: AGM vs Gel Battery for FT-897D?  (Read 55396 times)
N4SRN
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Posts: 305




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« on: October 03, 2014, 05:51:14 PM »

I'm thinking a battery box and battery for my Yaesu FT-897D, for home use as a backup and for portable use. I read that gel batteries are on the out and AGM the preferred primary option. But I don't know...

I'm looking for an off-the-shelf solution and considering the WMR setup as follows:

1. DC-to-GO Battery Box w/RIGrunner & Super PWRgate http://www.westmountainradio.com/product_info.php?products_id=dc_special

2. Battery
a. Sealed Lead Acid 79 Amp Hour AGM Battery (20 Hr Rate) http://www.westmountainradio.com/product_info.php?products_id=M24SLDA
or
b. Gel 73 Amp Hour Deep-Cycle Battery (20 Hr Rate) http://www.westmountainradio.com/product_info.php?products_id=gel73

3. Powerwerx 30 Amp Desktop Switching Power Supply with Powerpoles http://www.westmountainradio.com/product_info.php?products_id=ss-30dv

I'm sure there are cheaper options, but does this look to do the job?

What reasons to choose Gel vs AGM battery?
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Bret/N4SRN
Bedford, NH  USA
W6EM
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Posts: 1666




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« Reply #1 on: October 03, 2014, 07:07:13 PM »

AGM and Gel cells are both lead-acid batteries.  Whether the electrolyte is absorbed in fiberglass mat between the plates or mixed with an inert filler, both are valve-regulated lead acid batteries.  Meaning they will "burp" off gas pressure that accumulates during high rate charging.  Ideally, you don't want them to burp.  So, they are not sealed as some are led to believe.  If they burp gas, they lose electrolyte, and capacity.  So, don't charge at a rate higher than what the manufacturer recommends.

As for the Power Gate, be careful.  If you use your supply to power the radio directly, at 13.8V, it won't be enough to properly recharge a lead-acid 6-cell battery that has been significantly discharged.  You should disconnect the battery and use a charger that is capable of supplying more current (called equalizing current) than what a fixed-voltage 13.8V station supply could.  As such, you should charge the battery back up before you reconnect it to the Power Gate so that the power supply and battery float voltage are the same.  The reason fro the equalizing current is to help make sure each cell gets equally charged.
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N3QE
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Posts: 4921




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« Reply #2 on: October 03, 2014, 07:11:51 PM »

If you are using it portable (deep discharge) you want to go with the gel cell. If the battery is there as a backup not to be often discharged deep, then go with the AGM.

The 30A power supply you mention is great for running the radio from 120V, but you don't want to use it to maintain battery charge. You want a real battery charger too.
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W8JX
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Posts: 12081




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« Reply #3 on: October 04, 2014, 04:19:38 AM »

Today for portable I would not lug heavy gel cell batteries. I would use lithium. It is more expensive for sure but it supports more charge cycles and has about 4x as much stored power per pound vs  lead gel cells. If you are going to lug a 40 lb battery you would do better to lug a 40lb generator. There a several 1000 watt or less generators out there and gas is about 6.3 pounds a gallon.
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
KD0SFY
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Posts: 451




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« Reply #4 on: October 04, 2014, 12:59:52 PM »

There are deep cycle AGM and there are deep cycle gel. 

AGM is basically a modification of gel cells by using glass mats to keep the gel in contact with the electrodes. 

AGMs can be shipped by air and can be mounted in any position, whereas gel cells often cannot. 

AGMs are often lighter than the equivalent rated gel cell. 
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W6EM
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Posts: 1666




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« Reply #5 on: October 04, 2014, 03:45:20 PM »

Today for portable I would not lug heavy gel cell batteries. I would use lithium. It is more expensive for sure but it supports more charge cycles and has about 4x as much stored power per pound vs  lead gel cells. If you are going to lug a 40 lb battery you would do better to lug a 40lb generator. There a several 1000 watt or less generators out there and gas is about 6.3 pounds a gallon.
Don't forget to bring along the oil for that deep-discount H F machine.  2-cycles don't like 6.3lb unleaded by itself.  And, the attendant noise.......

Besides, this is 2014.  Add my vote for the LiFePo cells, plus a fold-up solar array to charge them.  Have lugged enough lead acid VRLA batteries in my time.

Looks like you can buy 4-10AH cells for about $72 plus brackets and jumpers from Battery Space dot com.  Double the price, but probably worth it.  Couldn't find the terminal voltage discharge characteristics, though.  At rated 3.2V per cell at full charge, wonder what does it look like at 20%.
« Last Edit: October 04, 2014, 03:47:49 PM by W6EM » Logged
W8JX
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Posts: 12081




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« Reply #6 on: October 04, 2014, 03:47:51 PM »

AGMs are often lighter than the equivalent rated gel cell. 

Given that mat replaces some of gel in battery it should be a little lighter but since it a little less electrolyte too it would have a slightly lower power capacity too.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W8JX
Member

Posts: 12081




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« Reply #7 on: October 04, 2014, 04:06:14 PM »

Don't forget to bring along the oil for that deep-discount H F machine.  2-cycles don't like 6.3lb unleaded by itself.  And, the attendant noise.......

There are 2 stroke and 4 stroke low power units out there making 1000 watts or less and with 2 stroke gas is premixed and a gallon lasts a long time and no crankcase oil to change or spill. Heres a few 4 strokes less than 28 lbs dry.

http://www.northerntool.com/shop/tools/product_200487786_200487786

http://www.homedepot.com/p/Westinghouse-1-000-Watt-Digital-Inverter-WH1000i/204633550?N=5yc1vZbx9nZ1z0z72o#specifications
« Last Edit: October 04, 2014, 04:10:37 PM by W8JX » Logged

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Ham since 1969....  Old School 20wpm REAL Extra Class..
KB4QAA
Member

Posts: 3257




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« Reply #8 on: October 04, 2014, 04:07:47 PM »

Will you be performing aerobatics or hanging sideways off the side of a mountain while transmitting?

If not, there is no reason to buy more expensive Gel cells.

Gel cells have one vulnerability compared to AGM.  If charged at too high a rate they can develop pockets where the gel pulls away from the plate causing loss of capacity.  Use a quality charger designed for gel cells.

AGM's do not have any less capacity compared to an identical rated Gel cell.

p.s.  AGM's perform well at odd angles because the mat holds the electrolyte against the plates, and you don't have 'sloshing' while carrying them.
« Last Edit: October 04, 2014, 04:16:42 PM by KB4QAA » Logged
W8JX
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Posts: 12081




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« Reply #9 on: October 04, 2014, 04:56:34 PM »


AGM's do not have any less capacity compared to an identical rated Gel cell.


The key word is rated. A AGM has a lower energy density because electrolyte is less dense. To get same capacity in same size you have to shrink lead with reduces peak current. No free lunch.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
W9FIB
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Posts: 2103




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« Reply #10 on: October 04, 2014, 08:15:42 PM »

Mr. Know it All has spoken!
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Happy being an Amateur Extra!
Nothing says CB on my printed license.
Ares/Races but no lights or crown vic.
W6EM
Member

Posts: 1666




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« Reply #11 on: October 04, 2014, 08:29:30 PM »


AGM's do not have any less capacity compared to an identical rated Gel cell.


The key word is rated. A AGM has a lower energy density because electrolyte is less dense. To get same capacity in same size you have to shrink lead with reduces peak current. No free lunch.
Puzzling.  That doesn't make sense.  Energy density would be Wh or Joules per unit total battery weight.  Dropping electrolyte total weight vs a vs not using clay in the electrolyte by itself would tend to raise, not lower the energy density.

Now, if you had said that the fiberglass mat requires more electrode surface area for equivalent energy storage, e.g., more lead, then yes that would raise the battery total weight and drop the energy density.
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N4SRN
Member

Posts: 305




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« Reply #12 on: October 05, 2014, 05:57:31 AM »

Interesting option here http://www.westmountainradio.com/pdf/BuildYourOwnUPS.pdf for home backup DC power.

Small generators look promising too, except for the noise.

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Bret/N4SRN
Bedford, NH  USA
W6EM
Member

Posts: 1666




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« Reply #13 on: October 05, 2014, 07:05:12 AM »

Interesting option here http://www.westmountainradio.com/pdf/BuildYourOwnUPS.pdf for home backup DC power.

Small generators look promising too, except for the noise.


A couple of mis-truths from the site: AGM batteries can and will suffer the same gas release and life-shortening venting that gel cells will if overcharged and gassing occurs.

Power Gate gizmos do not, I repeat, DO NOT allow for proper charging of a depleated lead acid battery by simply reconnecting the base regulated supply to the battery.  Your lead acid battery will have a shortened life and lower Ampere-hour capacity if not properly charged back up after discharge and properly floated after charging.  Probably the reason for WMR offering a new "power-guard" module with over and undervoltage sensing is the likelihood that some hams will crank up the station supply to better charge the battery but can cook the radios in the process, if well above 14V.  Easily built from a couple of LM432 shunt regulators and a P-channel MOSFET.


If you want to invest in a lead-acid station battery, at least buy (if not build) a multi-cycle intelligent charger from A&A Engineering.  Their chargers are based on the TI UC3906 IC.  You can build your own from scratch from the ARRL Handbook.  Boards and article copies available from FAR Circuits. farcircuits.net
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AA4HA
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Posts: 2384




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« Reply #14 on: October 05, 2014, 09:35:50 AM »

Just my 2 cents;

I have used gel-cell batteries that were originally purposed for emergency lighting packs and found that they seem to have a lower current capacity than a wet-cell or AGM battery. Also when they are chronically overcharged they go irrevocably bad.

Dissecting a gel-cell battery that had been chronically overcharged I found that the gel electrolyte had micro-bubbles entrained into the gel. I can see where this would mess up the current capabilities of the battery as these micro-bubbles would limit the surface area of the plates. Because they are entrained bubbles they do not have a way to easily escape (outgas) like a wet-cell battery and sort of get stuck there.

I have also taken apart AGM batteries. Most notably the spiral wound type. With those I found that there is a thin mat of fibrous material that is saturated with electrolyte between the spiral wound plates. This means that there is more plate-electrolyte-plate making the battery surface and a higher current content to the battery. The electrolyte, while not a liquid, seems to be a thinner version of what is inside of a gel-cell. To me, this implies that any gassing that happens in an AGM battery would be free to make it to the vent and not form little bubbles that get stuck in between the plates.

I have had good luck with AGM batteries and even replaced the battery in my car with an Optima Yellow-Top that is about 2/3 the size but with 1/2 times more cranking amps than the conventional wet cell battery.

Any lead battery is going to be heavy. Wet Cell and AGM's are pretty dense. Gells seem less dense and I think it is because there is less mass to the lead plates. Thinner plates can be a bad thing because once that lead goes into the electrolyte you can end up corroding the plates to nothingness.

For weight I use some very expensive LiPro batteries for my backpack radio. I cannot afford to go the Lithium rechargeable route with everything.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
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