Running a battery charger off gas generator

[pepperhead1963]

I have a coleman sport 1850 gas generator that has a 15amp DC charger as well as two AC outlets. I need to charge my Surrettes this time of year due to lack of sun.  My battery bank is four S530s for about 1000amps at 12 volts.  So the question is:

I have an AC battery charger that can put out 12amps, if I plug in the charger into the generator unit and attach to batteries as well as attaching the DC charger, will the charger handle that?  I understand running things off modified sine wave, is not recommended sometimes, but I was wondering how the charger will react to being plugged into modified sine wave then converting back to DC

Thanks

[Kevin L]

The limiting factor is your generator.  It is rated a 1500 Watts Continuous 1850 Watts Peak.  Real basic calculation is (120 VAC * 12A) = 1440 W  + (12VDC * 15 A) = 180 W = 1620W

The Gen will be running hot and you could risk burning the coils.  I wouldn't run over 1200 Watts to get some life span out of the generator.  Or you could run hot and cycle it, so that you give the unit time to cool.

[pepperhead1963]

Ok, so do you think there is an issue with running a battery charger from modified sine wave to DC, I remember reading you should not run battery chargers (ie from electric razors etc) from modified sine wave.  But I was wondering about an a/c battery charger

[shay]

I use 10:1 (120 amps dc to 12 amps ac)

27. amps dc is 2.7 amps ac
    
2. 7 * 120 vac = 224 watts
   
   

I always wondered if there could be an interaction between the battery charger and the dc output from the generator so thought that the hot leads might have to be matched to avoid this or a possible shock hazard.

[kurt]

1. gas generators are not mod sign wave only cheep inverters are. gas generators put out a true sign wave its just that there voltage can be off with load do to poor regulation and that can cause  problems with some smart chargers or if the voltage is really low your battery charger will not put out enough volts to charge the battery.
   
2. if you read the instructions that come with the generator it will usually say that you are not supposed to use both the 12v charging and the 120v outlets at the same time.
   
3. Kevin L's math is all goofy because your 120v battery charger is rated at 12 amps at 12v not 12A at 120v
   

[tecker]

 If the batteries will take more than 15 amps that would be too much to as the gen charger is probably not limited (but may have overload protection). It may not kick out 14 plus needed for the charge . The charger may see the 12 or so volts from the from and shut down . Crap shoot . The generator will run the charger so that's a solid decision.  

 

[Kevin L]

Goofy it is.

[dlangley]

Hi guys,

     This is my first post here so I'll say hi first. I have had the same problem before. The answer is to limit the current the battery can draw from the charger by adding resistance in series. Using Ohms law E=I*R  14V/15A=.93 Ohm of resistance (12v charger should be closer to 14 check it and use the actual measurment). You also need to calculate the amount of power in wattage this resistor need to handle (It will get HOT). The formula for power is P=E*I so 14V*15A=210 Watt. So all you need is a 210 watt .93 ohm power resistor. A 1 ohm resistor is close and lower the draw to 14 amp. I use a dome lightbulb from an automobile to trickle charge car batteries. It keeps from boiling the acid out of them when they get charged enough the current draw drops I remove it because it causes a slight voltage drop and you need the voltage a little higher than the float voltage of 13.8V to charge them properly.

   I used to have battery repair manual I downloaded from one of the yahoo groups that explained what the exact voltage should be but I've lost it. If anybody knows which manual it could have been and knows where I could find it again, I would appreciate it.

Dean

[bob g]

for what it is worth

those little colman suitcase generators with the briggs or tecumseh engines

have a flaw that you want to look into before you do any long term running under

a good load.

that is the epa compliant crankcase vent pipe is routed between the aircleaner and the carb intake.

what happens is when the aircleaner begins to clog the vacuum that is drawn will suck all the oil out of the engine, resulting in catastrophic failure, don't ask me how i know!

if it were me, i would disconnect that vent pipe and either vent it to the atmosphere, like the old non compliant engines or reroute it to the air intake side of the aircleaner so that there is no vacuum imparted on that line.

the advice to run it at 1200watts max is good advice as well, running at the peak output will likely shorten the lifespan of the unit.

i used one for some time on a service truck and i even turned the rpm down to 3000rpm for 50hz, it would still run my power tools and my lighting,, and the engine run's longer, quieter and with less gas as well.

i don't know how this might effect the charging rate at the 12volt plug, if it is regulated it might do just fine at the lower rpm albeit at a lower charge rate maybe.

suffice it to say, i am no fan of these little generators, but with a bit of attention and modification they can be pressed into service and get the job done in a pinch.

far better it would be to build a small engine driven alternator combo with a good regulator for charging your batteries, then you could set the engine speed to something more tolerable with the result being a better system in my opinion.

bob g

[JW]

1963,

 If I were you, i'd run one or the other. I have studied the wiring schematics for my 5000w diesel, which has both DC output and AC output. It says expicitly in the manual, 'do not try to run a load on the DC circuit that exceeds its rated output- while running any-sort of load on the AC circuit. My genset will output 220 or 120vac, but only one or the other. With the DC its not recomended to use it at all, unless the AC is not being used. This makes sense to me, because Ive also pondered the use of 2 seperate DC inputs 'to a battery-bank under load'.

 In my mind, its better to leave the DC capabilite un-used, until you have to fall back on it, for emergency purposes.

 And why-not, most battery chargers(AC type) can output at least 50 amperes at 12volts.

 I got into this situation by an underpowered outboard alternator that only puts out 6amps @12v. Im running loads, my batt bank can carry them for so-long, yet volts will drop as im using these loads.

 Now take one of those 1000watt gas minigen-sets, I could plug in a 50amp 12v batt charger into that, then hook it to the batt-bank, but, I would be very sure, to disconnect the alt, from the outboard engine, before doing so. In that situation I could maintain battery bank voltage, without the DC output from the outboard.

 As long as I could maintain batt voltage under heavy loads, I really don't give a crap, about the DC output. In reality, im just offsetting the batt banks load with an AC source powering a dedicated charger. Since the AC side of the genset is flexing its muscle, its best not to stress it out, with the DC side running simulaniously.

But to answer your question- you would findout about any potential feed back thru the DC regulator the very first time doing such.

JW  

[JW]

"

The cylinder is insulated.... I'm not sure what else I could do better without really changing things a bunch.

Kind of fun - if you watch the video you notice sometimes the engine slows down/speeds up - that's in response to my batteries being fairly full and my heaters in the shop kicking on and off. When they come on, the voltage drops and the load increases slightly. It's very responsive to that stuff.... I have no doubt that if a good gust of wind came up the engine would speed up a bit. DanB-

"

http://www.fieldlines.com/story/2007/9/22/14553/7837

You see, to me, this makes perfect sense,

 Since, there can be a great deal of feedback measured, thru multiple charging sources to a single battery bank. Both the load and battery-bank are equalized simultaniously.

With the diode bridges, this force/power- can be accepted thru the doide bridges, hence out-ove phase circuits may be harmonized, thru a common DC buss, to a batt-bank.

 But this is not the case od harmony with the DC output regulator. Which will almost always 'short its-self out' when detecting anytype of imbalence within a circuit closed within the battery bank.

 AGAIN,

 it seems to be possible, to get away with such an imbalance of phase cancelling, if all of the, DC charging sources, are derived from a diode bridge, then placed in parallel with the DC circuit, not a regulator(or mosfet).

Seems to me, several wind-turbines connected in parallel thru DC rectifier bridges, to a common [DC]batt-bank are no problem.

 Somehow, conflicting frequences(hz) can be mechanically balenced. Generally this type of feedback will burn-up the regulator to the DC output in a small gen-set. But it does not seem to hurt a small farm of wind-turbines, when connected to a common batt-bank.

JW

[pepperhead1963]

Thanks to all, I understand about the quality of the lower end gennys.  I think I will beef up my solar so I dont run into this problem.  I have about 80amps of solar at 12v.  My battery bank is four surrete s530's wired in series/parallel.

I think I will use the genny's 12v charger only when batteries start to drop to 12v under load

[ka0spm]

The power consumed by a 13.8 volt charger is the voltage times the current period. So the wattage of a 15 amp load at 13.8 is 208 watts. Converting that to amperage at 120 volts is about 1.7 amps. Automotive or deep cycle chargers have transformers to convert voltage and neglecting small losses in the transformer they convert wattage in and wattage out only voltage and current change. If you connected several chargers the Gen. will use more of its output. One charger will only pull about 250 watts max from the 120v side.

Chargers are capable of 50 amp outputs but not for sustained periods. Most have a duty cycle of only a minute or so. Then cool for 10 minutes or so. Forget about 50 amp current on a charger, they only to boost a battery for a quick jump start. A better option is to belt drive a truck alternator that can supply 100 amps at 13.8 for battery charging. Any lawnmower engine can drive it as the full load horsepower is about 2 hp. GM alternators also have a built in regulator that prevents overcharging. This is the system I use to keep Ham radio working during power outages. All of my rigs have 12 volt capability so it is a perfect system.

[Boss]

That is good advice about the heavy duty auto alternator

As far as duty cycle on cheap automotive battery chargers, I have worked out how to override the long duty cycle.

On mine the charge on-time / off-time(duty cycle)is controlled by a thermistor under the paper of the transformer. http://en.wikipedia.org/wiki/Thermistor  

Install a PC fan in the case.

Works like a charm

The charger stays on longer.

[TAH]

Battery chargers that don't work well on modified sinewaves are the tranformerless fast charge type that most cordless tools have now. They tend to charge at a higher rate than intended and blow the internal fuses. Small wall wart types work perfectly fine.