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doubleeboy 10-22-2009 10:40 AM

Iota Charger with AGM batteries
Hi All,

Our new to us Dehler 39 has a Mastervolt 30 amp smart charger. Nice charger in theory, but it is not working quite like it should. It puts out 13.4 volts no matter how it set, AGM, gel, conventional. Its .6 volt diode compensation isn't working either, and all 3 idiot lights stay lit all the time even though ammeter shows we have gone thru the 3 stages and are now in trickle charge mode. So while I am currently keeping the batteries pretty well charged up it isn't the ideal set up and will have to be changed out sometime.

I have read the posts raving about Iota and am thinking about either the 30 or 45 amp one with the smart brain upgrade but am concerned that they do not have temp compensation and that they don't really appear to be for marine use, it looks like they come with a household 120volt duplex plug on them. I guess what I am hoping for is some reassurance that over the long haul they won't fry my spendy 2 8D house bank and how to deal with the power cord issue. I would also like to get some charge to my Group 27 start battery which is not AGM. It currently is not in the charge loop and relies on alternator only for charging.

thank you for your input

btrayfors 10-22-2009 02:08 PM


The Mastervolt is a good unit. I believe the first thing to do is to try to find out why it's not working properly. 13.2 volts is the float voltage. Have you tried the Mastervolt on a deeply discharged battery bank? Also, do you have other charging sources attached? Wind generator? Solar panels? If so, they may be "fooling" the Mastervolt into believing the battery bank is fully charged.

The Iotas are very wonderful chargers, in my experience. While they are not "marine approved" and do not have temp sensing, they are very well constructed and do extremely well in marine applications. Many others have found this, as I have (I have two of them, and have installed several others). They are economical, virtually RFI-free, tolerant of voltage fluctuations in the AC supply and, with the IQ4 option, provide true multi-stage charging. They also have an automatic "equalization" cycle if you haven't charged in over a week. It's not a true equalization (which would require 15.5VDC or more on a 12VDC battery bank) but it's helpful. Further, they seem to maintain battery capacity better than even high end chargers I have used (including a top-of-the-line Victron MultiPlus).

AGM charging voltages are VERY close to flooded battery charging voltages. I wouldn't hesitate to use an Iota charger on an AGM battery bank. Because of the PWM (pulse width modulation) technology employed, Iota claims they don't need temp compensation since they can't overcharge/overheat a battery. Maybe, maybe not (there's some discussion re: the type of pulsing employed). But, it's also true that temperature sensors can be off -- in both directions -- and can cause problems. Maybe that could also account for your problem, if the Mastervolt sensor is over-reading battery voltage.


doubleeboy 10-22-2009 04:28 PM


Thank you for reply. I have taken approximately 175-200 amps off the battery over the course of a day by running lights, refrigerator,and small inverter running a fan. Without letting the batteries rest they measured 12.13 volts when I took loads off. Flipped the switch to energize charger and amp gauge on panel showed 30 amp charge, a couple hours later, 15-20 amp charge and when I came back next day 1 amp charge.

The three lights showing bulk, absorption, float all stay on all the time. As far as I can tell I do not have temp compensation sensor hooked up to batteries. These are the second pair of batteries the boat has had, they are 3 years DEKA batteries. Batteries, and all terminals are very clean, no corrosion. The local Mastervolt dealer came and took a look and said basically that by the time you take it out send it to Europe, pay them a few hundred to look at it and maybe fix it you could buy a new unit from someone more reasonably priced. He recommended a Xantrex but did mention the service from them left a lot to be desired, if ever needed.

Luckily I am getting the batteries charged up (I think) they show 13 and change volts when on float and after a few hours rest with charger off 12.6 or a bit more. I suspect at one time the previous owner may have had the optional monitor as there is a hole in woodwork about the size of a monitor with a plastic cover in it now. Maybe it went of the fritz and was removed and charger is not behaving because of this, just a guess. I am tempted to have the local outfit give it another look, to verify the temp sensor situation and see if I can continue on using the Mastervolt. It sure would be nice if Mastervolt gave a rip about their smaller chargers but that is not the case, compounded by the European service only and the value of dollar to Euro.

I am concerned that when drained to approximately 50-60% charge that batteries are only getting hit with 13+ volts not the 14.4 you would expect when in bulk or absorption.

Thank you for your reply and input

btrayfors 10-22-2009 06:19 PM

Yes, that does sound like a problem (if you're only seeing 13.2V during all stages of charge). You definitely DO want to get charging voltage over 14VDC during the final stages, before the 13.2VDC float. Apart from that, it sounded pretty good except for the lights being on all the time.

Wonder if there might be a reset button somewhere. Do you have the manual? Have you queried Mastervolt direct (not the dealer)? They may have a better handle on it's weird behavior.

Sorry I can't be of more help.


doubleeboy 10-29-2009 04:41 PM

Bill, Thank you again for your input. I have all but given up on Mastervolt, I have heard nothing back. I do have a further question for you. There is a company that sells Iota chargers with a different voltage profile , I am curious if you have any thoughts on their statements and if you think its worth the considerable price increase they charge for the different voltage option they offer. link below. I am charging a house bank of 2 AGM 8D batteries, no other charging going on except for the 80 amp alternator with standard regulator supplying the 8Ds and start Group 27.

Southeast Marine Services :: Battery Chargers/Power Supplies :: Iota Power Supplies/Chargers :: IOTA Power Supply/Charger

Thanks again

btrayfors 10-29-2009 05:06 PM


The blurb in the referenced link is a lot of gobbledegook, IMHO.

First, the IQ-4 option, either external or internal, will allow a fast and full charge of your batteries. Iota chargers tend to put out more amperage for longer periods than most "smart" chargers.

Second, the "equalization" mentioned isn't a true equalization. 14.4VDC isn't need at least 15.5-16.0VDC for a 12V battery for the equalization cycle.

I do agree with the statement that these chargers should be mounted outside of engine spaces. But then I believe that ALL chargers should be outside of engine spaces, and batteries and external regulators as well. Get's much too hot in there for reliable, long-term performance from electronic equipment.

In my experience (I have one external IQ-4 and one internal IQ-4 Iota charger) over the past several years, these chargers maintain my T-105 Trojan batteries better than other chargers I've tried, including high-end ones like the Victron Multi-Plus.

The Iotas with the IQ-4 option have an automatic weekly "equalization" cycle, raising the voltage for a period of time if it hasn't been high for a week or more. Again, not a real equalization cycle, but probably helpful.

Further, both of my Iotas have a float voltage of 13.6-13.7VDC. Right where I want it, since IMHO 13.2VDC is too low.


doubleeboy 11-24-2009 11:56 AM

Hello Bill and everyone,

To clarify a "heat of the moment comment by me" Mastervolt did get back to me, their customer service is very good after the right person was contacted in Florida. I sent the charger to them and they determined that it was faulty and was not in their opinion repairable. They offered me my choice of Mastervolt chargers at dealer cost. I am considering that or the Iota. The tech at Mastervolt pointed out that a 30 amp charger was very small for a 2 8D battery bank.

Thank you again for the input

btrayfors 11-24-2009 12:14 PM


When deciding on the size of the charger required, you should consider two things:

1. the type of batteries you have; and
2. the type of cruising you're going to be doing.

AGMs can take all the amps you can throw at them (and are very good at burning up undersized alternators without good regulators). If you intend to charge the batteries when at anchor with, e.g., a 120-volt generator/battery charger combination, then you'll want a large-capacity charger in order to keep the charging time reasonable.

For a bank of two 8-D batteries, a 45 or 55A charger would be too small for this application. A 75A or 90A Iota, or other large capacity charger, would be more appropriate, assuming you have the needed generator power to run them. BTW, as an example, a Honda 2000EU will just run a 75A Iota, but not the 90A.

If, by contrast, you intend to be charging batteries mostly at dockside or while underway with the engine running, then a smaller charger would do the trick.

If you're talking about Iotas, I'd be mighty tempted to go with a DLS75/IQ-4 rather than a smaller one, since the price difference isn't that much and the savings in fuel would pay for the difference in very short order.



doubleeboy 11-25-2009 08:08 PM


Thank you again for your thoughts. I am tempted to go with the DLS75 with built in IQ-4 but wonder if it can really drive the Honda 2000EU. Checking out this website for a review it looks a bit dicey according to their measured watts, amps in use. Do you know of anyone who has powered the DLS75 from Honda EU2000i for a couple hours.


Thank you again

btrayfors 11-26-2009 07:26 AM


You're could be iffy, especially with AGMs which can take a lot of amperage for a long time.

Several posts on this and other Boards have been by folks using the DLS-75 and the EU2000i, but I believe they were with flooded batteries. Typically, charging amperages with flooded batteries scale back relatively quickly and, of course, they won't accept anywhere near as much amperage as will AGMs.

Note that the Iota specs are at 108 volts. Adjusting for 120V, the maximum draw of the DLS-75 is somewhere between the Honda's "rated" output and its "maximum" output (2,000 watts). So, I would guess that the Iota DLS-75 would place a pretty heavy load on the Honda and, with 50% discharged AGMs, it would likely be for an extended period.

Temperature plays a part, too, as output declines with high temperatures. So, if you're going to use the EU2000i as a power source, you'd likely be better off with the DLS-55/IQ4 which would be fully within the EU2000i specs.

JMO...would appreciate hearing from anyone with real-world experience using Iotas and AGMs and Honda generators.


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