Reduce Charging Time

[R_C]

I’d like to reduce my daily charging time. I know I need more amps so I’m looking for ideas to add additional amperage at a reasonable cost.

Right now I have three 4D AGMs in parallel for a 600Ah house bank and we use less than 150 Ah per day. I have a separate start battery for my main engine and another for the genset. When we bought the boat it had two 4Ds for a combined 400 Ah and an ancient charger. I added a Xantrex Truecharge 40+ and their Link 20 monitor and later replaced the batteries with the three AGMs. I have the TC40 connected to the house bank and the main start battery. With this setup it takes about 2.5 hours of genset time to put back about 100Ah.

I think it was a Nigel Calder book that suggested the maximum charge current should be 10% of the total Ah capacity, which is why I went with a 40A charger at the time. I’ve since learned you can safely charge at a higher rate. We don’t have an inverter and I don’t plan to add one. So, short of spending $900 or more for a good 80A charger are there other options? Is there a way to keep the TC40 and add another 40A charger?

- Rick

[btrayfors]

Rick,

I'd be mighty tempted to go for an Iota DLS-75/IQ4 or a DLS-90-IQ4. These are excellent smart chargers (with the IQ4 option...$29) and do very well in marine service even though they are not specifically approved for marine use. They are the best bargain on the market, IMHO. See, e.g., Iota Regulated Battery Chargers

If you're willing to take a chance on a new one but without a warranty, you can beat even those prices by a wide margin by shopping on eBay.

I've had one aboard my boat for several years, one at home for a similar period. These run 24/7. They are RFI-quiet and very efficient. They put out a lot more average current than do other similarly rated chargers.

They can even be combined....two identical models, that is, to double output. No, you really can't use them -- or anything else, for that matter -- with your existing charger. I'd keep that one for a backup, and use an Iota for quick charging on the genset.

JMO,

Bill

[R_C]

Bill,

Thanks for the information. I have been reading in these forums and there seems to be disagreement about the need for temperature compensated charging with AGM batteries. If an Iota 90A charger can be had for about $400 and a Newmar 80A temperature compensated charger is about $1100, why such a big difference in price? Aren't they both 3-stage chargers? Does temperature compensation more than double the price of a charger?

- Rick

[Pete7]

You are only using 25% of your battery bank. Battery chargers will put a large mount of amps in to start with but as the batteries reach nearly fully charged the rate of charge drops off dramatically until the modern chargers reach a float charge voltage. Also are they sealed AGMs so you need to charge them at a lower voltage compared to open lead acid?

How about taking one of the house batteries out of the bank and moth balling it so you have 450 amps. Greater draw on the batteries yes, but the 40 amp charger will charge them faster because it can put in large amounts whilst the batteries are down.

We have 2 x 110 amp batteries with a 40 amp 3 stage charger but the batteries are open lead acid so can take 14.8 volts providing you keep an eye on the water level. We use about 100 amps in harbour per day but the charger only takes just over an hour to reach a float charge.

Pete

[btrayfors]

Rick,

There are several reasons. First, Iota does not target the marine market. They are a large organization which mostly serves the solar and industrial markets. They make chargers for a number of other brands. They haven't even bothered to get "marine certification", despite the fact that their chargers are built extremely well and -- according to their engineers -- certainly are "ignition safe" in normal use. Their specifications and performance are exceptional, in my experience. However, I believe that it's best to use them only on diesel boats.

AGM battery charging voltages are very close to flooded battery voltages. I would have no hesitation in using an Iota charger with AGMs, though they might not be suited for, e.g., gels which are much more voltage-intolerant.

RE: temp compensation, this is problematic. Problematic because the Iota's don't have it and their engineers claim it's not needed due to their PWM design, and problematic because even chargers with temperature compensation can be thrown off (misled) by temp sensors which don't report actual temps reliably. Lotsa stories about temp sensors under-reading (very dangerous) and over-reading (limiting charging current unnecessarily). I've had conversations with factory reps who are pulling their hair out because of the bad sensors out there.

Iotas clearly are not for everybody and every situation. But for many, including the application you described, I believe they are a good fit.

Bill

[R_C]

My batteries are sealed AGM. According to the technical manual they are valve-regulated lead-acid (VRLA) AGM. According to the TC40 user's guide the charge profile for an AGM is almost the same as lead-acid. Here are the absorption voltages:

Lead-acid: 14.0 (hot), 14.4 (warm), 14.8 (cold)
AGM: 14.0 (hot), 14.3 (warm), 14.6 (cold)

I deliberately sized the house bank at 600 Ah to minimize the daily depth of discharge in order to prolong their life. Using only 25% of the Ah capacity is exactly what I want. While away from shore power I never run the genset long enough to reach a float charge. In fact, I normally stop charging in the absorption phase when the TC40 remote display's 20A LED is lit. Pete, I have to question your math. How can you restore 100 Ah in an hour with a 40A charger? With most of my charge time in the bulk phase I still get less that 100Ah restored in 2.5 hours of charging.

Bill, thanks for the additional Iota information. You raise a good point about temperature compensation. I am using the TC40's optional battery temperature sensor. But I have no way of knowing if it is working or accurate and it overrides the charger's hot/warm/cold switch.

I like the thought of a 90A charger but the AC requirements of the Iota 90A are a concern. At 108VAC its maximum current draw is 21A. That's not a problem for my 7.6kW genset but that means a 30A breaker and 10AWG wire. Is that correct?

[Pete7]

R_C, yes agree the maths don't add up because I don't currently have any way of measuring the amp hours so instead have to guess the consumption of each appliance and add them up. With two teenagers believing we are still connected to the national grid this can be quiet difficult and vary wildly. What I can see is the voltage drop after 1 - 1.5 hours of charge, to a float charge at 14v although this will still be adding a charge.

Why do you need the engine start battery connected to the charger? I wonder if this is taking extra amps that could be directed into the house bank.

Pete

[R_C]

Pete,

I really don't need the main engine start battery connected to the charger but I figure it's taking less than 5% of the charger's capacity. Since the TC40 can handle three banks I decided to make sure the start battery was always ready. I thought about disconnecting it after the first charge before we launch following a six month layup. But I can see from the Link 20 that the house bank is getting 38-39A during bulk charge so I would get at most another 5Ah in 2.5 hours if I disconnected the start battery from the charger. I'd like a much better improvement.

- Rick

[btrayfors]

Pete,

30A breaker on the AC side, yea. 10 guage wire, nay. I'd use AWG6 or even AWG4, depending on length of run. Don't skimp on the wire size for chargers and inverters.

You need a 100A fuse or breaker on the DC side, too, for the 90A Iota. The Iota 75-amp model (DLS-75/IQ4) is sometimes a better choice depending on things like:

- generator size
- available AC power and circuit breakers

Don't forget, the Iota chargers put out more average power than many other chargers. The 75A model puts out a true 75A for a long, long time when charging in the bulk mode. It doesn't cut back quickly like many chargers. So, in some respects, the Iota 75 will recharge batteries as fast as, say, a 100A "normal" charger.

Bill

[Pete7]

Originally Posted by btrayfors

Pete, 30A breaker on the AC side, yea. 10 guage wire, nay. I'd use AWG6 or even AWG4, depending on length of run. Don't skimp on the wire size for chargers and inverters. Bill

My thoughts too, bear with me I have to convert, but we use 16mm2 wire for 40 amps and a 6 foot run from charger to batteries. Thats greater than your 4 AWG and looks like engine starter cables. We use a 60 amp fuse on the neg and 50 amp, one for each of the two positive leads.

R_C, I take your point about charging the engine start battery after a six months, but do wonder if it is still needed. However with a 7.6kva on board you ought to be able to run a small town so was wondering about multiple battery chargers one for each battery rather than one large one (which was your original query), but that is probably not cost effective either.

How much more charge do you think you can put in? we do loose water with 40 amps going into 220 amp battery bank, but with open lead acid batteries I am not to concerned and there is a plan to increase the bank with extra battery. Like you we want fast charging, some of our favourite European harbours only allow charging in the mornings so it would be socially unaceptable to run either the engine or honda genny for long periods.

Pete

[motion30]

I installed two 55amp Iota chargers for my 500 bank Due to ac amp draw of the chargers one is hooked to regular shore power and the other is hooked to the number 2 side of my gen set When on just shore power one charger run, no problem as I am at the dock and in no rush to charge With the gen set running both chargers are on cutting my charge time in half I have found the iota chargers to be a great units

[Cheechako]

If they are 3 step chargers is temp monitoring really necessary? especially with your bank size... I had 3 4D gels on my boat and never hooked up the temp sensor to my Ample regulator. (this with a 125 amp alternator) I had issues with my previous boat and the temp inter face. I would use about 100-120 amp hrs a day and spend about 1.25-1.5 hours keeping up running time. Do the Iota 3 steps function like an alternator 3 step regulator?

[R_C]

Bill, the 10AWG wire would be for the 30A AC circuit. On the DC side I am using very large conductors (can't remember the gauge) of only 2 to 3 feet from charger to batteries. The Iota chargers come with a 3-prong AC plug. How did you connect yours? Did you run a 20A AC circuit to a duplex receptacle near the Iota 75A charger? I've done lots of household AC wiring (in fact my entire house). Are there any special considerations for marine AC wiring?

Pete, my VRLA AGM batteries are sealed so I can't monitor the electrolyte. Charging a 600Ah house bank with a 90A charger is acceptable and I should be able to put 150Ah back in the batteries in less than two hours. That would be great. And I might get away with 1.5 hours a day depending on our power consumption. I just don't like interrupting the serenity of a quiet anchorage with the noise of our genset.

- Rick

[btrayfors]

Rick,

Re: AWG10 wire, understood. Yes, that's OK for the AC side.

Best to wire in a 20A receptacle, and plug the charger into it, especially since you already know how to do it :-) If you were to cut off the plug which came with it and direct wire it, you might run into warranty problems if there turn out to be any issues with the charger.

Be sure to get the IQ4 smart charge capability. This can be either built into the unit, or plug-in. Some models come with it already installed; others don't. Doesn't really matter which you choose. I have one of each.

Cheechako,

Yes the IQ4 functions as a smart multi-stage charger, and includes a weekly automatic "equalization" boost if there hasn't been another outside charge during the interval.

Bill

[Pelagic]

Originally Posted by R_C

I deliberately sized the house bank at 600 Ah to minimize the daily depth of discharge in order to prolong their life. Using only 25% of the Ah capacity is exactly what I want. While away from shore power I never run the genset long enough to reach a float charge. In fact, I normally stop charging in the absorption phase when the TC40 remote display's 20A LED is lit.

I agree with your AH size reasoning Rick.

I sized my House bank to consume only 10% in 24hrs at anchor and with my AGM’s keep them in the 72% to 82% State of Charge range therefore getting Full Bulk charging whenever I turn on my generator.

After 82% SOC Bulk charging drops dramatically and you are burning fuel for little return, so I stop there. (With AGM there is not stratification issue)

I kept my old (50a) charger connected to new bank together with my new charger (70a) and use both for this type of charging profile. Once past 82% I turn the 50a charger off if still running the gen. (24v system)

Best advice is to invest in a good monitor and play with charging profiles keeping in mind that if you continually draw down to 50% SOC, I understand you will shorten the lifespan of batteries