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Old 10-04-2009, 15:41   #1
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Gel and AGM Charging Voltages

I am considering buying GEL or AGM 12 volt batteries - around 100Ah each.

EastPen makes the MK/Deka brand. This is EastPen's writeup for their GEL and AGM batteries:

http://www.mrsolar.com/pdf/mrsolar/B...ech_Manual.pdf

Page 11 has the recommended charge and float voltages for the AGM and GEL batteries.

For 80 to 90 degrees F:
AGM: Charge optimum=14.10 Charge Maximum=14.40 Float Optimum=13.20 Float Maximum=13.50
GEL: Charge optimum=13.50 Charge Maximum=13.80 Float Optimum=13.20 Float Maximum=13.50

Now, I have an IOTA DLS45 charger and the optional IQ4 charge controller. The IOTA puts out: Float Charge=13.56, Absorption=14.16, and Bulk=14.76

The IOTA may be a fine charger for regular lead acid batteries, but it appears that its voltages exceed the battery manufacturer's maximums and may drastically reduce the life of the AGM/Gell batteries.

The IOTA is supposed to have a single POT which adjusts all three voltages equally. I am thinking of finding the pot and changing the IOTA's voltages to be 13.20, 13.80, and 14.40
This should be within specs for the AGM battery.
For a GEL battery the BULK voltage is still too high, and would necessitate unplugging the IQ4 to eliminate the BULK voltage, and instead plug in the dual-voltage phone jack until the charging is mostly completed.

I am not a boater - but found many of your discussions about batteries interesting, so I joined the discussion board.

My AGM/Gell battery use will be for Amateur Radio.
On the bottom of page 10 is a chart on the number of discharge/recharge cycles the AGM and Gell battery can take before requiring replacement. It is a function of percent discharged. It looks like the GEL battery will last 2x to 3x as many discharge/recharge cycles. However, the GEL battery takes longer to recharge compared to the AGM battery - probably because it must use a lower charging voltage.

I have two solar panels on my roof (over 100 watts per solar panel) and a charging controller to charge 12 volt batteries. I purchased it in 1999, and the batteries are no good at this point. So probably the AGM is a better choice due to the speedier charging. Though using the IOTA charger, I can use either AGM or GEL.

Anyways - I am interested in your comments. Particularly about adjusting the voltages on the ITOA charger.

Howard
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Old 10-04-2009, 16:02   #2
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Howard,

Interesting questions.

First, I'm a ham, too, and I run all my radios from two T-105 golf-cart batteries (flooded, 225AH @ 12V capacity), maintained by an Iota DLS-45 w/IQ4 charger. The charger is left on 24/7. Batteries are now about 4 years old, and test almost new with a sophisticated Midtronics battery tester.

I have another Iota charger -- a DLS-55/IQ4 on the boat, which also maintains a set of T-105s which are dedicated to my windlass. Batteries also are very happy (charger left on 24/7 when dockside).

Now, about AGMs and gels and the Iotas.

First, AGMs charging voltages are VERY close to those of flooded batteries. I wouldn't hesitate to use an Iota with AGMs and I wouldn't change anything.

Second, I'd be interested in where you found the bulk, acceptance, and float voltages for your Iota. They haven't been very forthcoming in the past about this, nor have they had much to say about battery types.

About two years ago, at the start of a battery testing program, I had a long conversation with an Iota engineer. He told me that the Iotas use pulse-width modulation (PWM) technology, and that the charging voltages are well above 15VDC...momentarily. He said the charger was designed to provide a full charge and that the pulsing design helps to eliminate the need for equalization.

Unfortunately, I haven't yet hooked one of my Iota's up to an oscilliscope or spectrum analyzer to see the exact qualities of its output....that I intend to do one day. But over the past 3-4 years using these guys I have noticed that they maintain batteries with a greater capacity -- without equalizing -- than do other "smart" chargers. For example, my house bank on the boat is maintained by a high-end Victron MultiPlus charger, and I notice with them a remarkable loss of capacity unless I exercise them and equalize them periodically. Not so with the batteries maintained by the Iota.

The Iota engineer also mentioned to me that the design was such that there was no way a battery could overheat or be damaged, and that it could be used with all types of batteries. I haven't verified that, so I can't testify to it. However, I can easily see that a pulsing technology -- used intelligently -- could provide charging at higher peak voltages without the attendant overheating a continuous charge would entail.

Typically, battery charging voltages are much too low to obtain a full charge. As Rick has noted elsewhere, the "bulk, acceptance, and float" voltage tables were probably developed by sales people, not engineers :-)

Hope this helps a bit.

Bill
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Old 11-04-2009, 00:50   #3
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The IOTA voltages are found here:

IQ Smart Charger for DLS Series Battery Chargers from IOTA Engineering

My concern is that exceeding the battery manufacturer's maximum voltage table may result in loosing water which can not be replaced in an AGM or Gell battery.

Regards
Howard
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Old 17-04-2009, 15:34   #4
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I have had several email conversations with IOTA engineers regarding their chargers. One of the true AGM battery killers is high absorption voltage. The IOTA chargers do not have temperature compensating circuitry and they do not intend to come out with a charger with temperature compensation in the near future. That being said, I do not recommend any charging source that is not temperature compensated.

For example, TPPL Northstar batteries have a 25C (77F) minimum float voltage of 13.50 VDC, a nominal float voltage of 13.62 VDC and a maximum float voltage of 13.74 VDC. At 40C (104F) those voltages become 13.14 VDC, 13.26 VDC and 13.38 VDC. 104F is not hard to acheive on the East coast in the Summer and is very easy to achieve most anytime in the Caribbean.
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Old 17-04-2009, 16:06   #5
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Originally Posted by CharlieJ View Post
I have had several email conversations with IOTA engineers regarding their chargers. One of the true AGM battery killers is high absorption voltage. The IOTA chargers do not have temperature compensating circuitry and they do not intend to come out with a charger with temperature compensation in the near future. That being said, I do not recommend any charging source that is not temperature compensated.
Charlie,

Did the Iota engineers explain to you why they do not consider temperature compensation to be necessary in their charger design? Are you familiar with pulse width modulation in respect to battery charging?

Also, RickM had a good posting around here earlier with some really good engineering info. Remember - Rick's the typical "he's forgotten more information about batteries in his career than any of us have ever learned" kinda guy!
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Old 17-04-2009, 21:36   #6
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Charlie,

Also, Rick had a good posting around here earlier with some really good engineering info. Remember - Rick's the typical "he's forgotten more information about batteries in his career than any of us have ever learned" kinda guy!
How "fast" you can reliably charge your battery.

AGM and gel-cell performance notes

Battery-Charging Voltages
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Old 21-04-2009, 05:46   #7
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Yes Charlie,

I agree with you. There's a lot of bull-s going around. Specs from manufacturers are there for a good reason. East Penn - the AGM/Gel manuacturer I mentioned earlier recommends only temperature compensating voltage limiting chargers.

However the IOTA charger is far more affordable. I figure that the indoor temperatures in my home will not exceed 80 degrees if the air conditioning is working. Thus I conservatively chose the 80 to 89 degree line from East Penn temperature charging voltage table.

Thus float at 13.2 volts, and charge at 13.5 to 13.8 (gel max) or 14.1 to 14.4 (agm max).

Now, if it actually 70 degrees in my home, I can use a higher voltage, but if I still use the voltage specified for 80 to 89 degrees, nothing bad should happen - it will just take longer to charge the battery. In other words, given it is 70 degrees I could have used a higher voltage and charged the battery quicker, but by leaving it at the lower voltage, the only downside is slower charging.

Now, the boaters need to worry about hot days where the temperature may reach 110 degrees F - so a float of 13.0 volts, etc.. And again, the only downside of using this lower voltage all the time should only be a longer charging time. However a longer charging time can be very inconvenient for you.

Sometimes I think there exists voodoo charging information from people who ignore every statement any manufacturer puts in writing - relying instead on a lifetime of instinct and verbal undocumented conversations with people trying to sell you their products.

I once worked with electricians at Bethlehem Steel that insisted on using far thinner guage wiring EVERYWHERE. They had 30 years of experience - they had no electrician license - 30 years of experience doing the job wrong. Wiring things that would fail a building inspection. After every electrical fire they concluded that the circuit breaker was defective - not their substandard thin gauge wires. Of course they enjoyed the massive amounts of overtime pay fixing the damage due to those defective circuit breakers. Some people have "opinions" that don't agree with established written standards and industry norms.

At the risk of offending the resident experts, I don't believe any bull you may have been told over the phone. If they won't put it in writing - it's just bull. IOTA has no PWM - if they did, they'd shout it from their web site and their brochures.

Anyways, have fun - and I hope your AGM/Gels last a decade.

Howard

Quote:
Originally Posted by CharlieJ View Post
I have had several email conversations with IOTA engineers regarding their chargers. One of the true AGM battery killers is high absorption voltage. The IOTA chargers do not have temperature compensating circuitry and they do not intend to come out with a charger with temperature compensation in the near future. That being said, I do not recommend any charging source that is not temperature compensated.

For example, TPPL Northstar batteries have a 25C (77F) minimum float voltage of 13.50 VDC, a nominal float voltage of 13.62 VDC and a maximum float voltage of 13.74 VDC. At 40C (104F) those voltages become 13.14 VDC, 13.26 VDC and 13.38 VDC. 104F is not hard to acheive on the East coast in the Summer and is very easy to achieve most anytime in the Caribbean.
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Old 21-04-2009, 06:51   #8
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Originally Posted by HowardZ
... I figure that the indoor temperatures in my home will not exceed 80 degrees if the air conditioning is working. Thus I conservatively chose the 80 to 89 degree line from East Penn temperature charging voltage table...
I believe that the significant temperature is that of the battery, not the ambient room temp.
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Old 21-04-2009, 08:07   #9
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You are correct, Gord, in this context, it is the temperature of the battery that is important not the temperature of the charging source.

One technical subtlety in Howard's post is his position on lowering voltage and its effect on charge rate. His claim that the effect of lowering the absorption charge voltage only lengthens the charge cylcle is not totally accurate. If AGM batteries are not aggressively charged to the manufacturers' specs, then chronic undercharging with subsequent sulphation and loss of cycle life will occur and the AGM batteries will not perform as designed.

Automatic temperature compensation is the best way to achieve the optimum performance of AGM batteries. Even so, with a multi-battery bank, you have to compromise on where the temperature probe is placed to be most representative of the bank's temperature. This position is even problamatic as a battery may reach 45C (113F) at the "hot" end of the bank while at the other end of the bank it may only reach 40C (104F) with the battery in the middle of the bank reaching 42C (108F). To continue the example from my previous post, these temperatures would lead to absorption voltages of 14.22 VDC "hot end"; 14.34 VDC "cold end"; and 14.28 VDC in the middle. By the way, this temperature distribution is not far fetched and, in fact, may not be as extreme as may be found in a hot engine room with a poorly designed battery box and no consideration given to battery cooling when the batteries are being heavily charged. So the question becomes, "Do we design to over voltage the hot battery or undervoltage the cold battery?"

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Old 21-04-2009, 08:40   #10
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GordMay, yes, I think you are correct.

Reading the East Penn manual:
http://www.mrsolar.com/pdf/mrsolar/B...ech_Manual.pdf

On page 13, there is a warning about chargers which measure ambient temperature as opposed to battery temperature.

Though I really like the IOTA chargers, this may make my strategy undesirable.

I own a Fluke Meter which comes with a sensor probe to measure temperature. But there's no way to automate the IOTA to respond to the temperature.

An IOTA may work OK at a fixed 13.2 volt float charge waiting for a power emergency necessitating the use of the battery. But charging the battery after the battery has been used during an emergency would require one of those expensive temperature compensated chargers or frequent manual temperature checks of the battery.

Would it really hurt things to just charge the battery at a lower than optimal voltage? Sure it will take longer, but it should charge up fully?

I'll have to think about this for a while.

Howard


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I believe that the significant temperature is that of the battery, not the ambient room temp.
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Old 21-04-2009, 11:17   #11
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HowardZ,

You're correct to be wary of anything you hear or read these days. However, you're dead wrong about Iota Engineering and the use of PWM technologies.

The Iota chargers DO use pulse-width modulation technology, and these have a number of proven benefits. To put this issue to rest, I asked the national sales manager for Iota Engineering to verify this, in writing. He took the question directly to the engineering department. Here's his response:

Quote
We do use PWM. We use a low pass LC filter to reduce the PWM to the component. We also regulate the voltage at the terminals to keep the peak voltage at whatever you want it set at. I have attached the power product guide. If you have any questions just let me know.

Errin Tribble
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National Sales Manager
800-866-4682 x224
IOTA Engineering Emergency Fluorescent Ballasts, Emergency Lighting Inverters, AC/DC Power Converters, and Automatic Transfer Switches
Unquote

We also discussed the matters of (1) marine certification; (2) different battery chemistries and Iota chargers; (3) temperature control/overheating; and (4) transfer switching products.

He told me that Iota has tested their chargers with all types of batteries, and has found no issues. It is his belief that the chargers will work with just about any battery. While this is counter-intuitive in terms of the hype about multi-stage charging, thermal runaway, and the need to carefully control voltages for, e.g., gelled and AGM batteries, it makes sense in terms of the PWM technology (see white paper referenced below). As I said earlier, I would not hesitate to use an Iota charger/DLS with an AGM battery.

RE: marine certification, two persons at Iota told me they'd thought about it and talked about it, but had earlier decided that the time, effort, and expense required wasn't justified by their marine market sales. This is changing: they're thinking about it again, and may move marine certification up on their list of "to do's". I encouraged them to do so ASAP in view of the high interest in Iota's that I've seen here and elsewhere.

RE: temperature sensing, Iota chargers don't have this because the PWM technology actually reduces the possibility of overcharging and thermal damage (see white paper referenced below). I would add that from my personal experience with temperature sensors on boats I have seen several instances where the sensors were providing erroneous information and causing serious battery charging problems. Even new sensors provide widely different results...some quite dangerous.

If you want to know more about PWM and it's benefits, suggest you read this primer from Morningstar:

www.morningstarcorp.com/en/support/library/8.%20Why%20PWM1.pdf

Disclaimer: I have no association with Iota Engineering. I'm just a very satisfied user.

Disclaimer #2: I do boat charging systems, battery storage systems, electrical systems, and related electrical/mechanical/electronics/communications work for a living. That doesn't make me an expert, but I sure see a lot of scary stuff :-)

Hope this helps a bit.

Bill
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Old 21-04-2009, 14:46   #12
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Well, I couldn't find the answer on the web, so I called EastPenn (manufacturer of the Deka AGM and Gell batteries) customer service dept.

The answer was what I logically thought.

The air conditioned room in my house will probably be 75 degrees in the summer. But, to be safe I plan to use 13.2v float and 13.8v charge voltages from the GELL charging table meant for 80 to 89 degrees. Being conservative with the voltages to try to avoid over-charging/over-voltage - which is a real gell and agm battery killer. The question whether using the lower voltage for the current battery temperature will result in undercharging/sulfate/reduce the life of the battery? I got the answer NO damage should occur, it will just take longer to charge the battery at the slightly lower voltage.

This made sense to me.

This is not in writing, but anyone can call and ask.
It was a quick long distance call - no waiting to speak with someone.

I only plan on using the battery power when there is an electricity outage. That happens less than once per year. So maybe the IOTA with the voltage adjusted for 13.2 for float 13.8 for charge will be OK. However, the IOTA does not seem to be the right recommended kind of charger to use.

During charging, I don't know when to lower the voltage from 13.8 to 13.2

Now, for PWM and the IOTA charger. I'm good at riling people, and hope I didn't get anyone too upset. A week or so ago I emailed IOTA about concern about using their charger on AGM or GELL batteries. He didn't think it would matter. I sent him the link to EastPenn's float and charging voltage tables. Then he replied that the IOTA is only a few tenths of a volt over maximum for EastPenn's AGM battery, but if I wanted to lower the voltages, there is a single screw which lowers all 3 voltages equally. On the older IOTA chargers, the screw is accessible from the outside of the charger, and for the newer IOTA chargers one needs to open the charger to access the screw. He stated that he had one customer complain that the IOTA charger made his battery get hot.

The PWM article web site - makes no mention of GELL or AGM in the article. So, it's not at all clear that PWM allows higher voltages on a GELL or AGM battery without destroying the battery. If the battery gasses - you've permanently damaged the battery. However, perhaps - maybe - you have years of experience using an IOTA with IQ4 on GELL and AGM batteries with no ill effects?

It may not happen right away, but I plan to buy an East Penn GELL battery. The GELL battery can handle 2x to 3x the number of discharge/recharge cycles compared to the AGM, and is also more resistant to overheating and I think its called run-away-overheating. The gell takes longer to charge, but I can live with that. I think I can just throw the IOTA 45 amp charger without the IQ4, adjusted for 13.2 v, and it will keep it charged for that rare electricity outage. However, I think I ought to buy a proper temperature sensor "made for GELL battery" automatic battery charger.

I love the IOTA charger - no interference/noise on my amateur radio. Utilitarian, quiet, works well.

I am just concerned. IOTA's web site makes no mention of GELL or AGM batteries. Don't you think - if the charger supported GELL/AGM batteries they would shout the fact on their web site to increase sales? I think they would. If IOTA chargers use PWM, who says PWM allows violating the maximum charging voltages listed by the Gell/AGM battery manufacturers? The article doesn't say this. The article doesn't mention Gell or AGM batteries at all. IOTA doesn't say this - at least I don't find it in their web site, nor the emails I exchanged with IOTA.

If IOTA would claim their chargers are GELL/AGM safe, then people can sue IOTA for any batteries ruined by their charger. IOTA does not make this claim - and they'd sell a whole lot more chargers if they did make the claim. If the IOTA supports GELL/AGM battieries, they'd make an official claim, sell more chargers, and earn more money - that's what bussiness want - to earn more money. They don't make the claim because it simply doesn't support GELL/AGM batteries, and they don't want to lose a bunch of money replacing people's ruined batteries.

I don't want to buy a $200+ Gell or AGM battery which should last a decade, and ruin it by using an incorrect charger. Looking at the price of these temperature-sensor Gell/AGM chargers - maybe I don't really want a Gell or AGM battery after all? Hmm.. $200 for a battery, maybe $300 or more for a proper GELL/AGM charger...over $500....Now at walmart or costco a 100 Ah deep cycle flooded battery costs about $60 or $70 and I already own an IOTA DLS-45. Hmm $60 or $500...$60 or $500?

When I'm not sure what to do - I take more time and think about it.
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Old 21-04-2009, 15:46   #13
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Howard, with all due respect to a fellow ham, I think you've overthunk this. You've got yourself so confused, you even missed the point about PWM charging and it's beneficial effects on ANY lead-acid battery.

By the way, charging at lower voltages WILL cause damage over time, because it allows sulfation (PbSO4 crystals) on the plates, which over time will reduce the capacity of the batteries and....if you keep it up...will kill them very nicely.

However, maybe economics will prevail. You've already got the Iota. Flooded batteries are MUCH less expensive than AGMs and Gels and Hybrids.

Why not go ahead with the flooded battery solution, and think about things for the next 5-8 years life expectancy with an Iota charger? Within a few years, anyway, battery technology will have advanced significantly.

Hint: watch the Caterpiller spinoff, Firefly Energy's Oasis battery, just coming on the market (currently restricted for the military and for trucker's). Just one of the new batteries.

73,

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Old 21-04-2009, 15:47   #14
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Howard,

Here's a few thoughts of mine on your application:

AGM batteries excel in three key areas:
  1. Their internal resistance is typically lower than regular FLA (flooded lead acid) or gel batteries. Since the resistance is lower, they can accept charge at a higher rate. Granted, internal resistance increases as the battery approaches a fully charged state, so the real difference is when you are in the bulk charging phase. An added benefit is that since the lower internal resistance doesn't impede charging current as much as FLAs or gels, they won't generate as much waste heat during charging - so they don't get as hot for a given amount of charge accepted. In practice, however, they will get hot, since you'll typically be charging them at a higher rate, assuming your charger is capable.
  2. Self-discharge rates are much lower than FLAs, and typically on par with gels.
  3. AGMs (and gels) are valve-regulated sealed lead acid batteries. You can typically mount them in any orientation - sideways, backwards, even upside down. Remember that gels were initially created for the USAF for use in fighter aircraft.
But your situation is much different than us cruisers. We live off our batteries, discharging them fairly deeply, and have only limited time to recharge - either due to genset/engine runtime (don't want to run it all day), available wind or sunshine if we have wind generators or solar panels.

In your situation, you are basically looking at emergency power backup, and you have a fairly large bank of solar panels to help charge if your electrical mains go down. Your batteries are probably at a fully charged state almost 100% of the time. They almost never get deeply discharged, so the fast charge acceptance of AGMs is moot to you. By the same token, since they're always being float charged, you don't have to worry about high self-discharge rates. And unless you're in an earthquake zone, you're probably not worried about your batteries being knocked over and spilling acid all over the place.

If I were in your situation (and I'm not), I'd go with standard FLA batteries and check the water levels on a regular schedule. They're much cheaper - and unless you factor in the time and effort spent to watch the water levels, they'll definitely be cheaper in the long run (assuming they're quality batteries) than either gels or AGMs.

FWIW, my boat has an 800Ah 12V house bank composed of four large 400Ah AGM deep cycle batteries. Since AGM's typically have a charge acceptance rate of 40% of capacity, I could bulk charge them at a 320A rate. But 320 amps of charging capacity gets pretty expensive to operate. I have a 125A Magnum Energy inverter/charger as my primary, and an Iota DLS-75/IQ4 as my secondary. I typically run both simultaneously off my genset, and they'll put 200A in for a short while, but of course that tapers off as the bank charges. I could throw in my 190A main engine alternator as well, but the long term cost of extra diesel burned and engine wear isn't worth it.

If my boat sat at a dock all day, a 20A charger would suffice to float charge my bank. If I lost shorepower and I had to run off batteries for a while, the 20A charger would be taxed to its fullest when power returned, but unless I drew the bank down faster than the charger can replenish that energy, eventually the bank would recharge it fully. Sound similar to your situation?
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Old 21-04-2009, 19:08   #15
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For your application...and with the Iota being a concern in YOUR mind...you are better off with flooded. Get a premium flooded with water-miser caps and save your money as Bill and others have said.
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