Proper Charger/Controller for engine to alternator setup

5 Posts
Mar 29, 2007 10:44 am
Proper Charger/Controller for engine to alternator setup


I have a 6HP lister diesel engine which I would like to use to charge a battery bank.  My original plan was to purchase a generator head where I would plug in a charge controller to charge the batteries, but I figured I could get by more cheaply and more efficiently if I had a large alternator hitched up to a charge controller.

At this point, I want to just see if I can get this thing to charge a battery bank and then, when I feel comfortable with the setup, I would like to expand it to include solar and perhaps enlarge the battery bank.

My alternator is a 14V 175Amp Leece Neville (4830LC) and I would like to purchase four 420AH Trojan batteries.  I plan on charging to 80% with a 50% discharge rate and equalize on the weekend. 

Can anyone out there recommend a really good charger/controller that can charge this pack (840 AH)in a reasonable amount of time given this configuration?

Many thanks in advance,

351 Posts
Mar 29, 2007 02:00 pm
Re: Proper Charger/Controller for engine to alternator setup


I am not sure that there are any advantages to using a charge controller with your alternator. I would be tempted to hook the alternator to the batteries and see how it works without a controller.

The output is going to be governed first by the rpm that the diesel is running at. (Have you thought of throttle control ?) It will produce 60 amps at an alternator rpm of about 1200-1300 rpm. Secondly the alernator will regulate the amperage based on the charge state of the batteries.

4-5 hours of run time should accomplish the charge you are after. 

The setup you are trying will work, but isn't real effecient. You are running the 6hp engine to do about 1 hp worth of work.

5 Posts
Mar 29, 2007 03:55 pm
Re: Proper Charger/Controller for engine to alternator setup


The output is going to be governed first by the rpm that the diesel is running at. (Have you thought of throttle control ?) It will produce 60 amps at an alternator rpm of about 1200-1300 rpm. Secondly the alternator will regulate the amperage based on the charge state of the batteries.

4-5 hours of run time should accomplish the charge you are after. 

Thanks Ken.  I appreciate your reply.  Since that test won't cost me any (more) money I can give it a try.

The alternator outputs 175Amps at 6000RPM's.  The engine running RPM is 650RPM with a 24" flywheel.

When you mention that the alternator can charge 840AH in 4-5 hours do you mean when the alternator is at full output or do you mean when it's outputting at 60Amps?

If the latter, then wouldn't it take about 14 hours to charge at an alternator output of 60 Amps (840AH/60A)?

Also, would I have to constantly fiddle with the throttle to adjust the amount of charge going into the batteries?

My rationale for the controller/charger is that if the controller is intelligent enough than it can be programmed and give the batteries what they need when they need it (including equalization) without me fouling things up.

Also, it would be able to give me visual indication of what the state of charge the batteries are at. 

Anyway, I'd like to try it your way to see what happens, but ultimately I would like the comfort of a charger/controller.  So if any one has suggestions for one, I would be delighted to hear them.

On another note, I tried spell checking my post using the spell check button and I found that the spell check feature you say "less than stellar".


351 Posts
Mar 30, 2007 04:42 am
Re: Proper Charger/Controller for engine to alternator setup


What is the alternator pulley ratio ? If it is 2:1, that will give you 1300rpm on the alternator at the 650 engine rpm. A 3:1 ratio would be 1950 rpm.

You said you planned charging from 50 percent to 80 percent on a daily basis. That would be about 252AH daily, or 4.2 hours at a 60amp rate.

You should not have to fiddle with the throttle constantly. I would set the engine at a good rpm (to deliver the bulk amperage I wanted) and let it run until the amps start dropping off, then you can lower the engine rpm.

If I were going to hook up a charge controller, I would want to disable or remove the electronic regulator on the alternator. I would probably use a rheostat to let me control the alternator output. Many electronic regulators do not see a charge controller as a load, so they back the amps way down, leaving the controller very little (if any) amperage to charge with.

5 Posts
Mar 30, 2007 09:06 am
Re: Proper Charger/Controller for engine to alternator setup

What is the alternator pulley ratio ? If it is 2:1, that will give you 1300rpm on the alternator at the 650 engine rpm. A 3:1 ratio would be 1950 rpm.

I haven't received my alternator yet (it looks like it's going to be delivered today but DHL is handling it so even though it's at the facility 10 miles away from my house, I should proably get it by mid April sometime) and it doesn't come with a pulley.

I was trying to figure out what size pully to put on it.

Using the equation:  generator pully size = (engine pully size * engine RPM)/generator RPM   

I can change the pully size by determining what RPM the engine and the alternator should run at. 

Originally, my uneducated instincts told me to max the RPM of the alternator to its highest comfortable RPM (6000 RPM) to output the 175 Amps.  I wanted the largest pulley I could put on it (to avoid slippage) so using the engine stats of RPM = 650 (that's highest comfortable engine RPM) and Flywheel = 24" and alternator RPM of 6000, my pulley size is 2.6 inches (pretty small don't you think?).


You said you planned charging from 50 percent to 80 percent on a daily basis. That would be about 252AH daily, or 4.2 hours at a 60amp rate.

I can see where you got the 4.2 hours (252/60) but I'm not sure where you got the 252AH. I plan on using 4 Trojan 420AH batteries which is a total of 1680AH.  I discharge to 50% (when the batteries reach 840AH). I need to bring the batteries up to 80% of their capacity (1344AH).  To do so means that I need to charge 1344 - 840 AH = 504AH.  504/60 is 8.4 hours.

Please let me know if I'm way off the mark here or if I've misunderstood where you are coming from.

Acutally this is all very encouraging because this means I can significantly increase my pulley size along with my comfort level.  If I drop the alternator RPM's down to 2000 (which, according to the specs, generates 140 Amps), I can put about an 8" pulley on the alternator (and have the engine run at 650RPM). 

This also means that I can charge 540AH in slightly less than 4 hours. Or, up the alternator RPMS to 3000, put a 5.2" pulley on it and generate 160 Amps which would charge the 540AH in around 3 hours.  I'm getting the alternater RPM's and Amp output from the Leece Neville spec chart for that alternator.

I would set the engine at a good rpm (to deliver the bulk amperage I wanted) and let it run until the amps start dropping off, then you can lower the engine rpm.

OK. Now here is where I hit a roadblock -- what instrument would I use to monitor the the amperage going into the battery pack?  Also, what instrument would I use to monitor the battery usage (an e-meter?)?

If I were going to hook up a charge controller, I would want to disable or remove the electronic regulator on the alternator. I would probably use a rheostat to let me control the alternator output.

Now this is kind of beyond my knowlege and abilities. I'd like to learn how to do something like this, but it looks like I'd need to spend more time learning electronics. 

So let's say I go the route of alternator direct to the battery pack.  How would I equalize the battery pack and bring it up to 100%?  Would that simply be running the engine alternator for a longer period of time until the pack came up to 100%?

Thanks so much for spending time answering my questions.  I really appreciate it.

351 Posts
Mar 30, 2007 03:39 pm
Re: Proper Charger/Controller for engine to alternator setup

I am assuming that your 420ah batteries are 6 volt. (L16H or equivalent ?).  When you put 2 in series, you get 420AH at 12v. Parallel two of these sets (4 batteries total) you have 840ah at 12v. So, 50% discharge is 420ah. An 80% State of Charge is 672AH. 672ah-420ah=252ah.

I am not sure that your idea of driving the alternator off of the 24 inch flywheel is the best idea. What type of belt and pulley are you thinking of?  Personally, I would look for two pulleys, one for the alternator and one to mount on the engine shaft (or bolt to flywheel).  A diesel engine crankshaft pulley and an alternator pulley of some diesel pickup  or diesel powered equipment should give you the ratio you need with “stock” parts from a parts store or junkyard.

I am not real familiar with the Lister engine, just read some specs and seen pictures. Does it actually throttle or does it just run at the 650 rpm ? If the 650 is a set speed, I would probably use a 3:1 pulley ratio, putting the alternator at 1950 rpm and yielding something just under the 140 amps.  If 650 rpm  is an idle speed, what is the max rpm ? If it can be throttled, I might use a lower pulley ratio.

The 140+/- amps is a max output figure of the alternator based on the rpm, without regulation.  The actual amperage produced will be a factor of the battery state of charge/system voltage.  When the battery is low, you will get the 140 amps.  As the State of Charge climbs (and the battery voltage climbs) it will take fewer and few amps for the alternator to push the system voltage to 14 volts (or 14.2 depending on which regulator is on it). The regulator will back down the alternator to lower amps so the system voltage never exceeds the setpoint.  As you are attempting to charge the last few percent of the battery, it may only produce 20 amps (or what ever), despite the alternator rpm of 1950. 

You need to think of the regulator as a charge controller.  It is one, although it uses a different algorithm than a charge/load controller designed for RE service. And it, goes off-line when the engine is shut down.

So yes, running the engine longer will bring the battery to 100 percent charge.

As far as monitoring the system, an amp meter and a voltmeter will give you the data you need. You will have to learn to read and interpret what the meters are telling you. Here is a good article on that subject.

163 Posts
Mar 30, 2007 09:51 pm
Re: Proper Charger/Controller for engine to alternator setup


As Ken says, your alternator will come with a built-in regulator that will maintain a constant voltage output regardless of the rpm you have it set at, and thus the amps output will be dependent on the voltage, IE state of charge, of the battery bank that you are charging.

Standard automotive/marine alternators are not ideally suited for recharging batteries in RE systems, but you might get better advice in a yachting forum where people living on small sailboats are accustomed to using a combination of solar panels, small wind generators, and small diesel engines to generate their power. Ample Power is one company that makes the type of controller that you're thinking about, but I'm sure there are many others.

If you tell us about your complete setup then we may be able to recommend some alternatives. For example, it might be more efficient to have your lister generator started and stopped by the inverter and have a genset on it producing 120v/240v ac directly which your inverter can use to charge the batteries.
5 Posts
Mar 31, 2007 06:32 pm
Re: Proper Charger/Controller for engine to alternator setup


As fate has it, I am also building a power system based on a 6hp Lister, with 4 Trojan 420AH batteries. I am still assembling it, but might have a few pointers.

1. I assume your Lister is a CS? ("cold start," water cooled, 700 pound monster). This is what I have. It is designed to run at 650rpm, so constant fiddling with the throttle isn't really the way to go. The 650rpm figure is NOT idle speed, it is the only speed. While there is some range of realistic speeds possible from these engines, over-speeding a cast-iron flywheel engine is an explosion waiting to happen. This danger is very real.

2. Running off a drive belt that rides on one of the 100lb flywheels is done all the time. It is called "allmand drive" I believe, and is most easily done with a serpentine automotive belt. Just get an appropriate pulley for your alt, and you're in business. It sounds shaky, but works very well.

3. A bigger concern is the idea that this whole setup will work just fine from empty batteries (50%) right on up to float. I don't think that's optimal. The Lister (like many diesels) likes to operate under load, not freewheel along under light load.

4. I plan to run a regular AC genhead and use the power for large machine tools, while a xantrex battery charger takes the "extra" power to charge my batts. This will let me run a smaller solar panel array.

5. You may already have this, but is THE resource for Lister-type engines. The HTML design is pretty "old-school", but George knows his stuff.

Let us know how it turns out for you! I could use all the "field data" I can get, seeing as how our power systems are cousins.  Smiley

5 Posts
Apr 4, 2007 03:24 pm
Re: Proper Charger/Controller for engine to alternator setup

First of all, I would like to thank everyone for participating in this discussion.  Ken, Jonn, Ed/Lowell and others, thank you very much for your information and for sharing your expertise.

At this point, I'd like to back up a bit.  I know that most RE systems should be designed and built for a specific purpose.  But in my case I simply want to see if I can generate my own power.  It's a learning experience for me to eventually build a complete system for my house.

That being said, I'd like to build an RE system around my 6HP Lister using biodiesel.

The only gear I have right now is a 6HP lister and a 175Amp 14V alternator from a bluebird bus.

From this point, lets say I have four Trojan L16H's and $1,500 to spend on this project whose purpose is to charge a battery bank using this engine and somehow get that electricity to an outlet in the house.

The batteries will be discharged to 50% and then I would like to charge them to 80% with an equalization charge once per week.

The options are to either use the alternator to charge a battery bank or to get a $450 generator head (can generate up to 5KW but because of the 6HP will generate around 3-4KW) for the lister and get a charge controller to charge the batteries.

One guy swore by the big honkin' alternator and Balmar charge controller method, but from what I'm hearing on this forum, the alternator method does not seem like a good idea mainly because of the voltage regulator in the alternator.

Other's have pooh-poohed the idea of getting a gen head and a charge controller because most charge controllers (the alternator pundit said) are inefficient.

Both arguments make sense to me, but they contradict each other. Each argument acuses the other of being inefficient. 

If I go with the 5KW gen head, then what charge controller would be best suited for the purpose?  How long would it take to charge these batteries from 50% to 80%?  Also, what type of inverter would I need to get the electricity to my house?

Similarly, if I go with the alternator, I'm imagining that I would have to remove the voltatge regulator.  At that point, what other equipment would I need to complete the system?

Thanks again,


5 Posts
Apr 6, 2007 02:58 am
Re: Proper Charger/Controller for engine to alternator setup


I know, starting out to produce your own power can be very confusing! I am not really an expert, but I have been messing around with my system for a while, and can tell you how I have  dealt with some of these issues. I am sure a real expert would have a good laugh at my setup, so take this with a grain of salt... Wink

re: efficiency. This might be a red herring. Infernal combustion isn't really that efficient to start out. If efficiency is the name of the game, then a straight solar setup wins every time. Of course, we already have our Listers! Cost efficiency is another type of efficiency that can be pretty important. I have heard of people recovering the waste heat from listers for space and water heating. I plan to try this (hot tub!).

re: alternator or genhead. Well, these were my thoughts. I have some big loads I want to run, too big for an affordable inverter setup. My genhead can run all the electric loads in my cabin, including an electric oven. Presto, I'm producing my own power, without messing about with anything else. By using the power directly, I am avoiding the inefficiencies (heh, heh) of battery storage and inverter losses.

Why store power at all? So I don't need to run the gen all the time. Yes, it is a Lister, not one of those screaming cheapo hardware store generators, but still. With a transfer switch, I can choose either genhead power, or switch over to my modest-sized true sinewave inverter/solar system. This is big enough for the microwave, CF lights, etc. I should point out that fancy-pants inverters can handle all this load switching business for you, which is nice. I have a really scary-looking Chinese model that makes sine waves, period.

So why did I go this route? I needed power NOW, within my budget. A genhead/transfer switch gets you making your own AC power today. Now I can sit back and play with my batteries, add some solar panels, etc.

351 Posts
Apr 6, 2007 05:48 pm
Re: Proper Charger/Controller for engine to alternator setup


I think that the confusion here is what are you attempting to build ?  Are you just trying to cobble together something that will provide a little power that you can play with  ?   Lets call that option a tinkering project.  Or are you trying to build a small but real energy system ?

I have been assuming that it is close to the tinkering end of the range, correct me if I am wrong on that.

If it is the tinkering project that you are just going to experiment with, and are not relaying on it for X amount of daily power, you are fairly close. I would slap the alternator on the Lister, wire up the batteries, buy an el cheapo Automotive/RV type inverter, and run the power to wherever you want to play with it.  After you have it up and running, you can see how it works. Then you can make decisions like the automotive type regulator isn’t doing the job for me. Or perhaps you might be happy with it. With this approach you won’t have a lot of money invested, and you will be making your decisions with a greater knowledge base.

If you want a real energy system, you never start at the generation end.  As John pointed out, you start at the load end.  I need to support X kilowatt hours a day. You then work backwards towards the generation, sizing everything appropriately.

Two totally different approaches.  A) I am going to build some thing, generate some power and limit my load to what ever the system can provide.  Or B), I need to support this load, and I will build the system to support it.

You mentioned a Balmar controller. It is an automotive type (or boat) regulator that is one step above what you have. It is better at handling multiple battery banks, or in some cases multiple engines/alternators. But, I would not waste my money on it.  They are a great regulator for the boats, but if the regulator that came with your alternator doesn’t do the job, odds are the Balmar will not either, and you should then using a real RE type controller.

It is hard to make any type of equipment recommendation to you, because you have given no idea of your power expectations. But based on the battery size, I don’t think you should go larger than 1500 watts on the inverter.  1200 watts continuous will be 10 amps on the AC side and something around 110 amps on the DC (depending on the exact efficiency rating of the inverter) You would only have about 2 hours of power at that rate, and that would be a bit rough on the batteries. But you could support 120 watts for 24 hours, or something between the to extremes.

You seem real stuck on that phrase of operating between 80 and 50 percent and equalizing weekly.  Your batteries will last longer if you work a little higher in the state of charge scale.  For RE systems I try to keep the Batteries above 75 percent on a daily basis. Draw down to 50% occasionally during periods of low generation.  Just shifting your use to the 60-90 percent range (65-95 even better) should prolong your battery life.

Equalizing charges are debated.  At one end of the scale, I have seen some people recommend one for every 10 cycles or once a month.  Personally, I feel that an equalizing charge is a controlled “over cooking” of the batteries and they should be infrequent and only as needed. Done too frequently, they shorten the life of your batteries. 

Trojans statement on the subject from their FAQ’s is
"When do I need to perform an equalization charge?
Equalizing should be performed when a battery is first purchased (called a freshening charge) and on a regular basis as needed. How often this might occur with your battery will vary depending on your application. You will need to monitor your battery voltage and specific gravity to determine when equalization is needed. For example, it is time to equalize if the measured specific gravity values are below manufacturer's recommended values after charging (recommended value for Trojan Deep Cycle batteries is 1.277 +/- .007 at 80o F). Equalizing is also required if the specific gravity value of any individual cell varies 30 points or more. Reduced performance can also be an indicator that equalizing is necessary. Equalization should also be performed when individual battery voltages in a battery pack range greater than 0.15 volts for 6 volt batteries or 0.30 volts for 12 volt batteries."

One could argue that the statement can support either side.  I read it as, as-needed or required. I don’t see any mention of “preventative or just in case” equalizing charges.

5 Posts
Apr 7, 2007 12:14 pm
Re: Proper Charger/Controller for engine to alternator setup

It looks like I have a few obstacles that I need to overcome first.

1.  I don't know enough about renewable energy to ask intelligent questions.


2.  There are so many options that I really don't know what I want.

If I had enough cash, I'd be able to have a setup with solar and a generator and a battery bank that could give me 16Kwh per day.

But I don't have that.

It's a coincidence that Ed mentioned the generator/transfer switch business because I figured that would be the biggest bang for the buck and would provide me with energy using my generator and cooking grease/biodiesel.

What was putting me off on the gen-head was that it cost $450 plus freight.  Now that I see that Harbor Freight opened up a store near me and has a 10KW gen head for $300 (no shipping charges) that looks mighty appealing.

I know that I'll only get 3-4KW out of it using my 6/1, but if I set up a transfer switch in my house, I could run the generator during power outages and on weekends to run my well pump, septic pump and a few outlets.  I could also just get an A/C battery charger to plug into the gen head and charge a battery bank with the extra that I don't use.

Then, I could use those batteries with a rinky-dink Coleman inverter to either power a pellet stove if need be or perhaps run a light or a heater for the water in the chicken coop in the winter.

Yes, right now it's experimentation. But I'd like to have some constructive use out of my playing around.

But the first order of business is to get the engine assembled and running.  So it looks like I'm going to get the genhead and see what happens next.

Thanks for all the constructive replies.  I appreciate all of you who are participating in this discussion.

5 Posts
Apr 7, 2007 01:34 pm
Re: Proper Charger/Controller for engine to alternator setup


I think you are on the right track, as a $300 budget does not buy much inverter/solar panel! I would spring for a "real" charger, so as to avoid cooking your batteries, though.

I am sure you are aware, but just in case... when I mention "transfer switch" I mean a real 3-position, purpose-built transfer switch, not something cobbled together. Just google it and you will see what I mean. This is a must.

To begin to sort out RE in a miniature scale, without breaking the bank, I might suggest one of two projects:

1. Solar lighting. Not those dim units for sale at Home Depot, but mini RE chargers designed for outdoor lighting. Look here:

2. Solar water pumping. If you have power available, this is likely to be too expensive. I am beyond the grid, and this is how I cut my teeth on RE. My well is far away from the cabin, and I needed H2O before I needed real power, so...

Either of these smaller projects will give you an intuitive feel for solar, without breaking the bank.

Good luck!

13 Posts
Apr 18, 2007 05:48 pm
Re: Proper Charger/Controller for engine to alternator setup

I'm running a kubota 6hp diesel with a Delco 22SI internally regulated alt as a backup/additional charge source to my hydro and solar. This site has the way to go in using an internally regulated alt for charging. I have two diodes wired in as suggested, with a switch that returns the alt to normal operation.
What I've found is that when the batteries are low, the high output mode described is too much load for my engine, but the charge tapers off at about 14v. So after about 1/2 hour of normal alt charging I flip a switch (bringing the diodes in-line) that continues charging at a high rate for another hour or so, then let my RE system finish the charge cycle.
I'd really like to add a morningstar relay driver (sold here-check it out) to start the engine, and control the charging automatically.
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