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Battery charger for 700w outout generator?
We're coming into a few cloudy/rainy (I hope) days here in Southern Arizona. This made me think about periods of cloudy weather or camping under trees for more than 3-4 days with my trailer.  I'm going to be getting a little propane generator (I can't stand the smell of gasoline). It's a Ryobi, 900watts peak, 700 watts continuous. What I'm looking for is the best battery charger that will work with this generator's limited power output.

I have four of the el cheapo UPG 121000 100ah batteries. In a perfect world, they like to eat 20-30 amps per 100ah of capacity when deeply discharged, which of course, they'll never get close to that on a trailer that is not connected to an alternator.  I also have 680 Watts of solar, so they are staying very, very happy with the sunny days we've been having here, per the Victron battery monitor I have.  But the day will come when the solar panels will be inadequate to get the batteries back to 100% in a timely manner.  I have portable solar but that won't help on cloudy days.

I thought that recharging the trailer batteries was a simple matter of plugging the trailer into the generator, but then I read that would take forever. So I need to get a battery charger directly connected to the batteries that plugs into the generator.

My question is, how large/what brand battery charger can I get for use with a 700 watt power supply?  700 Watts is 58amps, but there is the loss factor, I don't know how much. I have a CTEK mus25000 (25amp) battery charger, which Hubby is scarfing for his van.  It seemed to do okay on house current (when I had a house) on my van batteries (300ah).  But feeding 400ah of batteries only 25amps seems inadequate. Any suggestions on the battery charger that will work with the low output generator? Or should I keep the one I have and have Hubby get his own? I don't want to have to run the generator hours longer than I have to if I can avoid it with a higher amperage battery charger.

Thank you, 
It is not so easy to know what the generator will actually be able to power, and its rating is at sea level. Up at altitude it will be able to provide less total wattage.

A charger which has power factor correction will deliver more amps into the batteries, for the same input wattage.

WHile I am biased. this could be a good application for a adjustable voltage power supply.

If the power supply acting as a charger can overload the generator at altitude, well then one can back off of the voltage potentiometer, lessen the electrical pressure, and the batteries will accept less amperage, and stay below the generator max continuous current at sea level or up at altitude.

My Meanwell rsp-500-15 is rated for 500 watts, but will feed a maximum of 614 watts, and it claims upto 94% efficiency in converting AC to DC, so this "should" stay below the 700 watt maximum of the generator, at sea level.

The problem with my specific power supply, is that the tiny Adjustmet potentiometer it comes with, is not designed to be turned often. It is only rated for 50 cycles, and one needs a tiny jewlers screwdriver to adjust it and a fine hand. Adjusting voltage while loaded with a depleted battery is more difficult as the battery will drag the voltage down.

I have modified mine with a 10 turn potentiometer, but this required removing the electronic guts from the casing, desoldering the legs to the tiny trim pot, and soldering in 2 wires into place, which will lead to the external potentiometer rated for many thousands of cycles. The transistors use the casing as a heatsink. On reassembly one must use a thermal grease in between the transistors and the 'silpad' and the casing.

The voltage range is 13.2 to 19.2v. It can provide 40 amps continuous at any point in this voltage range, but of course there is little use for voltages much over 15 for AGM battery charging.

At 600 watts output, it creates a lot of heat. It comes with a very loud 40MM fan.
I added two more very quiet fans, and more heatsinking to the casing's led and now the loud fan only comes on in 75f ambients and above at 40 amps output/ At 32 amps output or less, the loud fan never comes on.

So it is not really a plug and play solution. It could be until the pot wears out, but in theory one could fire up the generator and warm it up. Then fireup the meanwell, not connected to the well depleted battery bank yet, and adjust voltage to 14.5v or so, then attach the DC leads to battery. If the generator dies, disconnect meanwell from from the battery, fire up generator again, lower voltage to 14.25, connect to battery, see if it stalls. If it does not, then one can basically leave the Voltage pot in that position, forever at that altitude or less, or just know they have perhaps 50 total adjustments before the original voltage pot wears out and voltage and amperage jump around wildly afterwards.

HOw are your soldering skills? Back in 2014 when I modified mine I was pretty scared of taking on the task, but on hindsite it was pretty easy.

Peppering the casing adjacent to the transistors, with these very small stick on heatsinks will greatly extend its lifespan when maxed out providing 40 amps.

I cut holes in the steel lid for a 60Mm fan blowing in and an 80MM fan sucking out. I used Noctua fans. They are very quiet and efficient and effective for their amperage consumption

I put one of these style Wattmeters on teh DC output so i could see voltage, amperage, minimum voltage, watt peak, Amp peak, Watt hour and Amp hours:

BUt I just saw the product below which comes with 8awg leads. MOh Betta then the 12AWG leads provided with above product. I modified mine with 8awg, but this can go wrong with too much heat applied for too long on the circuit board and internal shunt.

There are other products for measuring voltage and amperage one should really have on the output of a charging source to see just what it is doing or trying to do. A separate batttery monitor is good, but one wants voltage reading closer to the output of the charging source so thay can check it when not connected to battery.

I use 45 apm anderson powerpoles on 8awg, but this too is not recommended as shoehorning it into the contacts is very time consuming. 75 amp anderson powerpoles would be better for this task, but they are significantly larger.

I am not really familiar with the power requirements of an Iota DLS-30. It says 400 watt maximum output with greater than 80% efficiency. One loses some of the altitude adjustabllity and 10 amps, and the voltages it chooses are not the greatest for every stage, but it is a pretty good all around charger/converter.

The IQ4 device turns it into a 3 stage charger, without it it is just a 13.6v dc 30 amp power supply. Some units are sold with the IQ4, some are not. Buyer beware.

There are other adjustable voltage power supplies even less expensive than the 86.40$ Meanwell rsp-500-15. But they might not be PFC, and their voltage range might not be well suited for battery charging. If one wants to search out other Adjustable voltage power supplies from Meanwell, they must have constant current limiting on overload.

Some other power supplies will have roll back current limiting on overload whih will back way off on charging amperage, some will have hiccup, meaning it stops entirely as long as the overload is present. Constant current limiting is best for battery charging, then roll back, and Hiccup, not at all.
Buyer beware.
[-] The following 2 users say Thank You to sternwake for this post:
  • Gunny (02-14-2018), frater secessus (02-14-2018)
Thank you, Sternwake!

My soldering skills are nil and the first option with the Meanwell was grossly intimidating (and scary) to me, reading it right off the bat.  

So, I went down to an easier (I.e., lazy) option you presented, the IOTA charger converter.  Those I like (and the newer models look sexy) and they are more idiot proof.  And I can order the custom cables to go with it from the genuinedealz folks.

But as I mentioned above, I want to pour the max amps into the batteries in order to keep the generator run time as short as possible. Not so much for efficiency, but to keep the noise to a minimum for me and more importantly, potential neighbors. I would like to use the DLS-45 vs the DLS-30. However the 45 might be cutting it close with the 900watt peak /700 watt continuous specs of the generator. So, I emailed them the question on which charger would be best.  

I will keep you guys updated with the process.  The generator shipped yesterday. I will make sure it works before getting the charger.  I would have gotten a larger lgenerator, except at 25 pounds, I'll barely be able to lift this one.

Just to show off, I'm posting my new, nice and shiny little display box for the battery monitor. I went ahead of put in extra USB and 12v outlets. And, for the heck of it, put in a toggle on/off switch. Don't have plans for the switch right now, but ill think of something.

Attached Files Thumbnail(s)
Thank you both for your posts. Even though I am totally ignorant when it comes to electrical stuff. I need more of plug and play regardless of extra cost. I'll hopefully be able to compensate someone for the information and directions etc when I start my build in a few months. I'm gathering all the materials, and items needed first. Yes I know..filling the wagon before I got the wagon. But do to time constraints when the time comes I will not be able to "run into town " to get the stuff I need due to working on the road most all the time. I've got a free storage building on family ranch (where I am actually going to do the build at). So while I'm on the road I just have everything I buy shipped there and they put it in my storage. When I get ready to take time off the road in a few months I'll go buy the shuttle bus and start the build.
The dls-30 with the IQ-4 battery charger is on the way, along with the Ryobi generator. With the frequent cloudy and rainy weather, currently on day 5, without a brilliantly sunny day for another four, I'm having to babysit the charge controllers. Because I'm not going below 85%, the charge controllers are only giving me one hour of absorption, then going to float. That's great, but according to the battery monitor, I'm still at a deficit, I haven't paid back the power I used last night while watching the Olympics.

So, every day after the chargers go to Float, I go back in and set them to Equalize for an hour. I programmed the Equalize voltage to the same as my absorption voltage. That one hour does the trick on partly cloudy skies, but during the all day rains, I had to do it three times, the panels were getting in so little. Using the generator once or twice a week with scrappy weather will eliminate the need to be here to babysit the batteries. I've just about run out of the money from the house sale, so I can't afford a new bank. Thank you, Sternwake.
One can also program float voltage to the same as absorption voltage if Absorption is not lasting for long enough. Those daily cycling, and with too little solar and a controller not holding absorption voltage for long enough, should consider this 'trick'.

Also consider that 'Float' voltage of 13.2 (flooded) to 13.7v( AGM) is basically for long term storage of fully charged batteries. Simply to prevent self discharge and cover any minor loads still on the system. Those daily deep cycling need to be skeptical of their charge controllers when it goes into float mode. Premature float voltage kills batteries when absorption voltage has not been held for long enough to finish the task. Thinking a premature float voltage will have enough time to fully charge the batteries before sundown, is extremely unwise in van dweller type of battery usage.
I think it is a crime when a charge controller reverts to float when the batteries are less than 100% charged. Some who anthropomorphise their batteries think that they appreciate a gentle topping up, but such intents is more like stopping all physical touch a few seconds before orgasm, day after day.

I do not have any excperience with the UB121000's personally, but I do know they say no more than 30 amps charge current per battery.

My Northstar AGM 90AH battery has always responded well to high recharging currents. When I notice it being a bit petulant and i can plug in, I drain it well below 50% and parallel my 40 amp meanwell with my 25 amp schumacher and hammer it with 65 amps and it accepts this much from below 50% for 22 minutes before voltage at battery terminals rises to 14.7v, which I find impressive for a 4+ year old battery witrh 700+ deep cycles on it.

AGMs do like to see the occassional higher recharging current. You can approach their upper recommended limit by recharging one UB121000 at a time via the Iota, though this might be a pain in the ass to accomplish.

I am not sure exactly the algorithm of the Iota, I believe it takes the battery to 14.8v at maximum amperage of the unit, holds it for 15 minutes, then drops voltage to 14.2v for 'absorption'. This is a bit nicer to the battery than holding it at 14.8v through absorption, but it does slow the process, which might not be very 'nice' if the next discharg begins before 100% SOC was reached.

I installed an Iota DLS-45 in my friends RV, replaceing a WFCO that could never get the batteries into the 14v range. The Iota got him another years use out of the batteries compared to the Wfco. More recently I replaced the 2 parallel 12v group 27's with some Costco Interstate 6v GC-2's, and while he has no real idea other than the idiot colored lights indicating battery charge, he is impressed with his battery capacity, even though it has remained basically the same.

I watched the Olympics last night for many hours too, but my TV only draws 1.1 amps. I find the 'slope style' skiing boring though.

I need to make up a power cord that I can put my clampmeter around one wire. I am currently building a system for a foreign couple's Van, and am amploying a PD9245 charging source, on a single group31 Crown1 AGM battery,. This battery says max charging current is 27.5 amps, and the PD has 45 available. I am not concerned about exceeding the max rate, as the max rates are generally listed to minimize warranty returns, and are not considering that exceeding that amperage could allow the battery to reach full recharge before the next discharge cycle begins, which will promote battery longevity.

HEat build up is the concern when providing amperage over the max 'recommended' , so I will inform the owners that on really hot days, with a depleted battery, If they plug in and use the PD 9245, to press the 'wizard/pendant"'s button to force it into 13.8v mode as opposed to the 14.5v mode. The PD9245 with the Wizard pendant can allow one to choose 14.4v, 13.6v or 13.2v, manually, and override the automatic stages. If I drain the battery and could isolate one wire and put my clampmeter over it I could see how many watts it actually pulls from the grid vs how many it delivers into the battery.

Ammeters are so dang useful
[-] The following 1 user says Thank You to sternwake for this post:
  • Cammalu (02-18-2018)
" Some who anthropomorphise their batteries think that they appreciate a gentle topping up, but such intents is more like stopping all physical touch a few seconds before orgasm, day after day."

What a great analogy!

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