150 amp alternator with 6.5 HP engine to charge AGM batteries

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
RV daytrader

RV daytrader

Active member
Joined
Feb 4, 2011
Posts
29
Location
northeast PA
I plan on doing a lot of off grid boondocking so will be using battery power only. My toyota MH is small with limited space for batteries. My plan was to get a  100 amp hour AGM battery cause from what I read they can be charged at 4X their amp hour rating (a 100 amp could in theory be charged at 400 amps, not practicle because of wire size and alternator size). But a 150 amp alternator could be hooked up to a 6.5 HP engine and safely charge a 100 amp AGM battery very fast.
I can get a new 6.5 HP engine from harbor freight for $120 on sale, a used 150 amp alternator with pulley for around $75, maybe $50 foe engine pulley, wire, brackets etc. I have a 2 receiver hitch on back which should hold this ok (total weight should be around 80-90 pounds)
Thoughts on how this would work out??
 
When I had an '86 Toyota Dolphin Class C, I replaced the stock 60 amp alternator with a 110 amp alternator from Northwest Off-Road. When the coach batteries (I had two) needed charging while boondocking, I just ran the truck engine at high idle for as long as it took. Fuel consumption was minimal. My "high idle control" was a stick of wood cut to the right length to wedge it between the seat and the gas pedal.  :D

http://www.northwestoffroad.com/parts/alternators.html
 
You read wrong.. The max initial charge rate for LIFELINE AGM's is 300 percent.. That is for LIFELIEN only, other brands are not as quick charging.

Other than that.. 150 amps alternator would need perhaps a 3HP motor, your six HP can run two of them.
 
this is from "alternators by Quick Start" q&a...

3.How much engine horse power does the alternator take?

An alternator typically takes about 1 HP (horse power) for every 25 amps of power generated. So, a 100 amp alternator will require about 4 HP at full output. Most alternators do not operate at full output for very long. 

I do read different info on on other sites...some say less, some say more! More research needed!!
 
What would be the benefit of running it with a separate engine as opposed to doing what Dutch suggested and mounting a high amp alternator on the mh engine? That, to me seems like it would eliminate a lot of cost, and hardware, not to mention extra weight.
 
With a big alternator you can dump a lot of amps in short term, but the rate at which the battery can accept amps quickly drops once the battery reaches 70+% of full charge. It will still take several hours to get to full charge, but it should reach 70-80% charge somewhat more quickly than with a smaller charger. [Exception: Concorde/Lifeline AGMS will charge in as little as 3 hours with a high capacity charger]

Concorde (Lifeline) rates their AGM at 4x its amp-hour rating but most other manufacturers rate theirs at only 25%-30% of the amp-hour rating (C/4 or C/3).  Furthermore, it is critical that the voltage be regulated for AGM charging and most battery manufacturers specify no more than 14.4v or 14.6v, regardless of amps. Automotive alternators often run to 16v or more at max output, so you may want to add a good quality regulator.

You would be better off with multiple batteries and perhaps not charging them fully. Each battery can accept a lot of current in its bulk charge phase, so running two of them to 80% charge takes less time than trying to get one to 100%.
 
Water Dog said:
What would be the benefit of running it with a separate engine as opposed to doing what Dutch suggested and mounting a high amp alternator on the mh engine? That, to me seems like it would eliminate a lot of cost, and hardware, not to mention extra weight.
Click to expand...

The main engine on my coach, when operated at full idle, sucks around 0.9 to 1.1 gallons per hour.

The six HP engine he's talking bout, perhaps 0.25 Gallons per hour at load and speed.

in short... Major fuel savings.. and at 3.00+ per gallon, soon to be 4.00 let's see, six hours a day for 7 days is 42 hours, or 42 gallons for the motor home and only about 10 for the six HP.. svings of 32 gallons or over 120 dollars.

Won't take long to pay for the hardware.
 
Make sure that you buy a good muffler.  That beast is going to be loud for you and your neighboring campers.

Unless you really run your batteries down to less than 50% capacity, expect to never be charging at over 80 or 90 amps and that will taper off as soon as you get a good charge going.  We used to have a high output alternator on our sailboat with a 3-stage regulator and almost never saw more than about 50-60% of the output rating even when first starting the charge.
 
John From Detroit said:
The main engine on my coach, when operated at full idle, sucks around 0.9 to 1.1 gallons per hour.
Click to expand...

I'm sure you are right about the fuel consumption on your rig John, and I agree with the logic, but don't you think the fuel consumption would be much less on the Toyota?
 
Water Dog said:
I'm sure you are right about the fuel consumption on your rig John, and I agree with the logic, but don't you think the fuel consumption would be much less on the Toyota?
Click to expand...

the fuel savings on running a 6.5 hp instead of a 130 hp would definately add up using it every day...plus the wear and tear would be on a $120 throwaway engine instead of the MH engine. the only down side is the extra weight.
 
Our little red Honda genny does all the above, PLUS lets us watch Sat TV, charge the ipod/phone/shaver/walkie talkie batteries, and even pop a bag of popcorn in the microwave, in it's whisper quiet mode, and only sips fuel...

Sure, it might have cost a bit more up front, but it's a nice compact, dependable package that's easy to handle... ;)
 
You must log in or register to reply here.

Latest posts

Members online

Total: 1,651 (members: 34, guests: 1,617)

Forum statistics

Threads
131,976
Posts
1,388,555
Members
137,726
Latest member
CampMike2270
Back
Top Bottom