Charging house batteries using engine alternator

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Back2PA

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I've seen threads discussing the apparent fact that it's more efficient to charge batteries idling  the engine vs. using the gen set. According to Spartan I've got a 160A alternator. Any thoughts/knowledge on what the output would be at idle? Going to be dry camping for a few days this month and will likely have use for this knowledge. Thx
 
Yes..... and No. The big question is how big is your battery charger? The one in my MH charges at 100 amps, the one in my boat at 150 amps. Running 1 to 4 cylinders (depending on your genset) is more efficient than running 6 in my MH. My genset and charger are designed for charging deep cycle batteries for long periods. They are designed to put out power for hours on end. They are quieter than the main diesel engine. My MH alternator is designed to recharge for short periods of time or less than maximum charge for longer periods of time. My Beaver owners manual specifically warns against using the engine alternator to charge up deeply discharged house batteries. It specifically says to use the genset and inverter/charger to charge deeply discharged house batteries.

So I would say that the apparent fact is false.

Ken
 
Another point is that you will not get anywhere near the amperage at the trailer connection that the alternator is capable of putting out. So if your plan was to just leave the trailer plugged into the 7-pin receptacle it would take a long time to charge the batteries.

Now if you connect directly to your tow vehicle battery while it is running, say with jumper cables, you are putting out a lot of amperage that, as pointed out, might not be good for deep cycle batteries.



Mike
 
Is it more efficient to idle the engine or run generator.

A big block V-8, or V-10 Gasoline or a big diesel will burn fuel faster at full idle than the generator will at full load.
Plus the alternator is very low output at full idle in fact on some ewngines, if you are in neutral the alternator can't even keep up with the engine's needs.

Bottom line; Run Generator, it needs the exercise anyway.. UNLESS you have the problem I have just now.
(Generator tail pipe rusted out.. Replacement on order.. Just waiting for it, Should have next week I hope. Install will ve a very very very simple job).
 
For 2-3 day dry camping any two battery set up should hold you well with conservation. I think I have managed with one and using the generator to charge while using  the micro and tv.
 
IV done it in a pinch.  But at ideal you not likely to get more then 20 amps of charge at the most. Which means 5 hr of ideling to get 2 100 amp batteries charged 1/2 way....
 
Batteries have a maximum charge capacity called saturation.  Most lead acid batteries will only  take about 10 amps per hour.  You can push the rate higher, but all you do is cause heat.  The batteries will overheat and are potentially dangerous.  Gel cell batteries can take a higher charge rate, but cost twice as much.  Most modern converters float charge or will put out 10 amps drop to  lower charge rates as the battery voltage comes up.  The best thing to do is plug you unit in to 110 volts.  If you have 200 amp/hour batteries at 10 amps it will take 100 hours to fully recharge your batteries.  I purchased a Honda 2000 I generator and when dry camping run that for a couple hours per day and that takes care of keeping batteries charged.  It uses very little fuel and is very quiet.  It will run up to 8 hours on a gallon of fuel.  My Generac 5.5 burns .8 gallons per hour.  You would be better off running your generator than the engine of you unit. 
 
garl02 said:
Batteries have a maximum charge capacity called saturation.  Most lead acid batteries will only  take about 10 amps per hour.  You can push the rate higher, but all you do is cause heat.  The batteries will overheat and are potentially dangerous.  Gel cell batteries can take a higher charge rate, but cost twice as much.  Most modern converters float charge or will put out 10 amps drop to  lower charge rates as the battery voltage comes up.  The best thing to do is plug you unit in to 110 volts.  If you have 200 amp/hour batteries at 10 amps it will take 100 hours to fully recharge your batteries.  I purchased a Honda 2000 I generator and when dry camping run that for a couple hours per day and that takes care of keeping batteries charged.  It uses very little fuel and is very quiet.  It will run up to 8 hours on a gallon of fuel.  My Generac 5.5 burns .8 gallons per hour.  You would be better off running your generator than the engine of you unit.

Is your 10 amp number referring to Bulk, Absorption or Float mode on your modern charger? Most sites I read, battery manufacturers and smart charger sites, state that up to 25% of amphour capacity is an acceptable charging rate. 10% is less than half that. Are you sure that's a maximum? Wouldn't the temperature sensor connected to the smart 3 stage charger keep them from overheating? Why do they put an inverter/converter/charger unit in RV's with a 100 amp charge capacity if a 400 amp battery bank can only accept 40 amps maximum?

When I do the math it comes out to 20 hours if you have 200 A/H batteries charged at 10 amps. And that assumes the batteries were totally flat, not a recommended practice. 100 hours seems awfully long, even taking into account a lower charge acceptance rate when almost completely charged.

Thanks, Ken

 
Sun2Retire said:
Aaaaannd.... there you have it. Genset it is
  The Alt. car, truck RV gas or diesel all the same is to power vehicle and maintain battery. But not a charger for heavy discharged batteries you will burn it up. Yes genset or solar. JS
 
Also, there's the voltage to think about, especially after running through some fairly small wiring and a trailer connection. Your battery will get a full charge at 14.4 to 14.8 volts -- at the battery. With a long cable run of undersized cable and a charge current of 10 amps, I doubt the charge voltage will make it out of the 13.x voltage range.
 
Bruce is Right.
Without a special "Voltage Boost" device, the Alternator in the Truck/SUV cannot charge the Trailer Batteries. They will only provide power while the batteries are being discharged by the Fridge, and similar loads.

Purpose built devices are made by Redarc and Ctek. It is also possible to create a home-brew Voltage Boosting system, feeding into a Solar Controller, but it's (ahem) a bit more complicated. I've done that, and power from my TV into batteries is a bit less than 300W, during "Bulk" charging. I can charge my pair of "typical" SLA batteries from 50% to about 85% in 2 hours, either driving or idling in camp.
 
As some one responded earlier, depends. In my older rv the weak link is not the genset but th the house inverter charge controller that puts out but a nominal amp charge rate. This can be replaced ( or modified) to charge at a much higher rate, and be "smarter." Its pricey, but worth considering if you are a boondacker. Whatever alternator/relay setup/ gauge wiring is connected to my house batteries from my Y2k V10 motor actually does a pretty good job charging the house batteries while idling. This is important if your gennie fails, or like me in camps where you aren't meant to run a gennie. Yes the RV idling is loud and I'm sure not as efficient as the Onan emerald 3500 , certainly  not as efficient as a yamaha or honda suitcase quiet generator. The V-10 in its own way (no taptaptap) is quieter than most quiet generators IMO. As far as charging off the alternator, I have an older diesel  stepvan that is basically designed to be a generator It was designed for roadwork. You put it in park, push a button and it revs at a higher idle sending current from its very high output alternator to a major inverter. Enough to power a chopsaw, a bunch of old incandescent lights and a table saw. Thank goodness for LEDs and Lithium battery tools. Even my table saw can now be run cordless. So again it depends. Even when plugged into "shore power" a house stock battery charger may charge less than a trickle, such is the case with mine. If you rev your engine in a pinch you may be able to charge your batt via the alternator pretty quick. As previously posted the type of batteries and how many amp hours you have will factor in. MY fairly low budget utilitarian work around to quicker more efficient charging is "install" of purchased a 40 amp "smart " with 110 amp engine start portable charger ( not a jumper pack, has no battery of its own ) the kind you plug in. I have it "tapped" into the wiring from house battery to an aftermarket  high wattage  inverter inside the RV cabin,  looks like all 0 gauge wiring there. I didn't clip the jumper clamps so I can remove it and use it "dual-purpose" Mine happens to be from West Marine. I've seen a nice one at the Home Despot from dewalt 30 amps and 80 amp "jump" but has an accessory charging option that can be hard wired as well as jumper clamps, usb charge ports and an AC outlet. The black and decker one is the WM's twin. Most of these have a battery recondition mode. I have this hooked up, so that when i have shore power or run my generator I can charge my 200 Ah AGMs quickly and "smart" If in a bind I can use the same unit to jump my rig from shore power or off a generator. I learned the hard way that the DC out from portable generators is super duper nominal. Like for charging RC toy batteries. but when I plug the portable charger into say a 1000 W gennie I can get charged up quickly or jump my rig. So those who answer right away don't do that do this, but rather that like the first respondent stated, depends. Very curious about the devices the earlier poster mentioned that are designed for your engine's alternator to better charge house batts. I'll research that. Neat! bet they are pricey like most marine and RV "stuff" Without being an electrical engineer or electrician one could test there out true charging rates from different sources using an ammeter, It would be awesome if someone posted their own scenario. Perhaps I'll get around to it.  Oh yeah, then there is ye old solar. Dont forget to plug your genni's court back into the RV 110 inlet/outlet If you have such a setup. I bought my rig used and had now idea about this. I'm sure in fancier and newer RVs you don't need to do so. Much of my 2000 Four Winds Funmover was built just well enough to get you "into the RV" and your credit card out. Thank goodness the e450/v10 ford chassis and drive train is super solid. Guzzle Guzzle.
 
garl02 said:
Batteries have a maximum charge capacity called saturation.  Most lead acid batteries will only  take about 10 amps per hour.  You can push the rate higher, but all you do is cause heat.  The batteries will overheat and are potentially dangerous.  Gel cell batteries can take a higher charge rate, but cost twice as much.  Most modern converters float charge or will put out 10 amps drop to  lower charge rates as the battery voltage comes up.  The best thing to do is plug you unit in to 110 volts.  If you have 200 amp/hour batteries at 10 amps it will take 100 hours to fully recharge your batteries.  I purchased a Honda 2000 I generator and when dry camping run that for a couple hours per day and that takes care of keeping batteries charged.  It uses very little fuel and is very quiet.  It will run up to 8 hours on a gallon of fuel.  My Generac 5.5 burns .8 gallons per hour.  You would be better off running your generator than the engine of you unit.

FYI batteries have min and max charge rates

flooded lead acid is typically C/6 to C/10

AGM is typically C/4 to C/8

for a 200 A/hr FLA battery that is approx 200/6 = 33 A to 200/10 = 20 A
and a 200 A/hr AGM would be 200/4 = 50A to 200/8 = 25 A

Lithium can be anywhere from 0.5 C to 10 C

i have some Lithium Titanate  ( LTO ) cells here in the lab i'm messing with that are 40 A/hr and they will charge at 150 Amps
and discharge at 200 A without issue..!



 
solarman said:
FYI batteries have min and max charge rates

flooded lead acid is typically C/6 to C/10

AGM is typically C/4 to C/8

for a 200 A/hr FLA battery that is approx 200/6 = 33 A to 200/10 = 20 A
and a 200 A/hr AGM would be 200/4 = 50A to 200/8 = 25 A

Lithium can be anywhere from 0.5 C to 10 C

i have some Lithium Titanate  ( LTO ) cells here in the lab i'm messing with that are 40 A/hr and they will charge at 150 Amps
and discharge at 200 A without issue..!

What does the capital C refer to/ stand for? Thanks for this equation.
 
garl02 said:
Batteries have a maximum charge capacity called saturation.  Most lead acid batteries will only  take about 10 amps per hour.  You can push the rate higher, but all you do is cause heat.  The batteries will overheat and are potentially dangerous.  Gel cell batteries can take a higher charge rate, but cost twice as much.  Most modern converters float charge or will put out 10 amps drop to  lower charge rates as the battery voltage comes up.  The best thing to do is plug you unit in to 110 volts.  If you have 200 amp/hour batteries at 10 amps it will take 100 hours to fully recharge your batteries.  I purchased a Honda 2000 I generator and when dry camping run that for a couple hours per day and that takes care of keeping batteries charged.  It uses very little fuel and is very quiet.  It will run up to 8 hours on a gallon of fuel.  My Generac 5.5 burns .8 gallons per hour.  You would be better off running your generator than the engine of you unit.

This is probably the most impt. charging rate knowledge I have gained. It is DANGEROUS to try and charge a battery to quickly. I am assuming that modern quality smart chargers don't allow for such a situation. Also it makes more sense to me why you wouldn't charge at 100 amps, that's enough to start most engines. Thanks for the info, also the approx fuel consumption of your house versus your portable charger. I'm tempted to ditch my onan. It's finicky. But it runs the AC, and its nice it sips (slurps) off the gas tank.
 
rickst29 said:
Bruce is Right.
Without a special "Voltage Boost" device, the Alternator in the Truck/SUV cannot charge the Trailer Batteries. They will only provide power while the batteries are being discharged by the Fridge, and similar loads.

Purpose built devices are made by Redarc and Ctek. It is also possible to create a home-brew Voltage Boosting system, feeding into a Solar Controller, but it's (ahem) a bit more complicated. I've done that, and power from my TV into batteries is a bit less than 300W, during "Bulk" charging. I can charge my pair of "typical" SLA batteries from 50% to about 85% in 2 hours, either driving or idling in camp.
Re "home brew" voltage boost in a nutshell risky: https://expeditionportal.com/forum/threads/alternator-voltage-boost-modification.193869/
 

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