Anybody add a second alternator for house battery charging?

[Mex-Busnut]

Dear Friends,

I am wondering how practical it might be to add a second alternator to our engine for running the 110-VAC inverter and charging the house batteries while running down the road. The idea is to NOT have to start my genny, unless we are parked.

I appreciate your input!

Thanks!

[Sean]

Steve,

IIRC, you have an enormous Delco 50DN alternator on the coach already -- hard to imagine why you'd need to add more alternator to charge the house batteries.  Or am I misremembering?

-Sean
http://OurOdyssey.BlogSpot.com

[prevosman]

Depends on how your coach batteries are set up.

On my coach I have the 50 DN 270 amp 24 volt alternator. That is ample to take care of the house and chassis battery banks. There is an isolator between the alternator and batteries so neither set can draw down the other set.

On coaches that have 12 volt house systems it is common to see a 24 volt alternator for the coach, usually a 145 amp capacity if the bus does not have over the road air, and the 50 DN set up for the house, so the owner can run a couple of AC units while driving. Those two sets of batteries are usually never connected to a common point.

What you do not get with two alternators is redundancy. If one pukes you still have the loss of battery charging on the house or coach.

If you are wanting more charging power so your can run bigger loads such as AC units, why not just crank up the generator, the most underused 1/2 ton of metal in our coaches. It takes similar amounts of fuel to drive a big alternator at capacity (and is tough on the alternator because of the heat generated) as it does to use the generator to make the power to run house electric devices.

[Ed Hackenbruch]

We have a 12v alternator that runs off one of the grooves of the 50 DN alternator pulley. We still have bus heat, 24v  running lights and starting batteries. We also have a 12v system running off of the house batteries. When sitting, we can charge them thru the inverter if needed. They are also charged by 3 solar panels.  This was all set up by the PO, only changes i made was to add 2 of the panels and buy a new inverter when the Vanner died. We also have a 110 system when plugged in to a pole.

[Mex-Busnut]

Thanks for your input!

This is my current 12-volt generator (external regulator) on the bus engine:

[Tikvah]

What makes more sense?  I have an MCI with a 24 Volt system.  Obviously there will also be plenty of 12 volt systems also.
I expect to have a set of 12 volt battery just for the 12 volt loads (I assume I need to???)

Can I keep my 12 volt battery charged from the center lug of my Vanner equalizer, or should I add a 12 volt alternator?

[Sean]

... why not just crank up the generator, the most underused 1/2 ton of metal in our coaches. It takes similar amounts of fuel to drive a big alternator at capacity (and is tough on the alternator because of the heat generated) as it does to use the generator to make the power to run house electric devices.

A common misconception, but it's not even close.

My 270-amp 50DN uses an additional 0.1-0.2 GPH to produce the extra 5-6kW I use for my house system going down the road (yes, I have measured).  By contrast, my generator uses 1.1 GPH to do the same thing, or nearly ten times as much fuel.  Even a more appropriately sized model (6kW instead of the 15kW monster I have) will use about 0.5 GPH, or 3-5 times as much fuel as the main engine alternator.  Not to mention maintenance -- using the main engine alternator does not put nearly as much extra "wear and tear" on the main engine as you will have on a separate genset.  Think about it -- running two separate engines to do a job that can be handled by just one is usually not the most efficient solution.

The big Delcos on most of our coaches are rated for continuous output, and the heat is very efficiently removed by the oil supply, BTW.  I would not advocate this approach with a more conventional, air-cooled alternator, which often are not rated for this sort of duty.

This is my current 12-volt generator (external regulator) on the bus engine:

OK, that's an air-cooled model, look like around 100-120 amps.  So probably you would benefit from some more capacity for the house bank.

One option would be to use this one for the house bank, and put a smaller model in for the chassis loads.  Without any passenger HVAC, most chassis loads will fit comfortably within the range of a 65-amp or so model.

What makes more sense?  I have an MCI with a 24 Volt system.  Obviously there will also be plenty of 12 volt systems also.
I expect to have a set of 12 volt battery just for the 12 volt loads (I assume I need to???)

How to handle house systems on a 24-volt coach have been discussed here many times -- check the archives.  But, no, you do not need to have a separate 12-volt battery system.  It is very common to use a 24-volt house system, especially if you plan to have an inverter, and use a battery equalizer to provide 12 volts for loads that need it.

Can I keep my 12 volt battery charged from the center lug of my Vanner equalizer,

Only if you wire it per the diagram supplied for that purpose.  At that point it ceases to be an "equalizer" and instead becomes a converter.

or should I add a 12 volt alternator?

Again, this subject has already been covered here many times, as well as in the magazine.  It is largely a matter of personal preference and what you are comfortable with, as well as what alternator you already have on your coach.  Frankly, with a 7.5 kilowatt monster on there already, I would not go to the expense of adding more alternator capacity.  Even the largest equalizer, assuming you even need that much, will be a cheaper alternative.

-Sean
http://OurOdyssey.BlogSpot.com

[Tikvah]

I don't understand how the inverter has anything to do with 24 volt 12 volt.   I guess I have miles to go in this learning curve.  But my impression is that my inverter changes the 24 volt DC power into 120 volt AC power.  How does that help with my 12 volt battery?

[bevans6]

For me, the decision point is the "killer app".  What is the ornieriest thing your house system is going to do?  If it's run the lights and the TV, anything can do that (OK not anything, but an old car battery and a $50 inverter can do that, has for years in my truck camper).  If it's also run the fridge, a microwave intermittently, a bit harder.  If it's run many house systems 24/7 and also run the air conditioner on the road, that is hard.  For me, that means a 24v nominal house bank, tied to the bus charging system if it is large enough, or with at least 150 amp 24v dedicated alternator and a 3000 watt inverter for lots of headroom starting motors.  It's entirely possible to run the normally small (under 40 amp) intermittant 12v loads from a 24 volt house bank (unless you get 8 volt batteries for some reason) with the equalizer.  

So what you end up with all depends on what you start with, what you want to do, and what you want to spend.  There are a ton of ways to get this done, many of them right...

Brian

[bevans6]

Tikvah, the inverter CAN have a lot to do with a decision to run 24 volt or 12 volt house systems, since it is usually the largest load and often the main charger aside from an alternator.  My personal rule of thumb (just mine, works for me) is deciding if I will run the air conditioner from the batteries at any time.  If I do, then I have to have a fairly decent house battery bank (I have 230 AH at 24 volt) and I have to be able to supply enough current from the alternator to run the AC through the inverter and all the other loads, and have some left over to charge everything (I have the Delco DN50 at 24 volts, so no problem as long as it is good to me).  If you don't have to run the airconditioner, it all gets a lot easier.

Brian

[Sean]

I don't understand how the inverter has anything to do with 24 volt 12 volt.

The inverter is designed to operate on one or the other.  If you have 24-volt available, generally you can get larger inverters than if you only have 12-volt available.  And all your cables will be much smaller for 24-volt models than 12-volt models, generally making a 24-volt setup bot less expensive and also more efficient.

I guess I have miles to go in this learning curve.  But my impression is that my inverter changes the 24 volt DC power into 120 volt AC power.  How does that help with my 12 volt battery?

Unless you have the type of inverter with a built-in charger, it doesn't.  But see above -- choosing a 12-volt house system will generally limit you to a 12-volt inverter, with its larger cables, fuses, switches, etc., and also limit you to a maximum of about 3kW per inverter, as opposed to around 5kW for a 24-volt model.

-Sean
http://OurOdyssey.BlogSpot.com

[prevosman]

... why not just crank up the generator, the most underused 1/2 ton of metal in our coaches. It takes similar amounts of fuel to drive a big alternator at capacity (and is tough on the alternator because of the heat generated) as it does to use the generator to make the power to run house electric devices.

A common misconception, but it's not even close.

My 270-amp 50DN uses an additional 0.1-0.2 GPH to produce the extra 5-6kW I use for my house system going down the road (yes, I have measured).  By contrast, my generator uses 1.1 GPH to do the same thing, or nearly ten times as much fuel.  Even a more appropriately sized model (6kW instead of the 15kW monster I have) will use about 0.5 GPH, or 3-5 times as much fuel as the main engine alternator.  Not to mention maintenance -- using the main engine alternator does not put nearly as much extra "wear and tear" on the main engine as you will have on a separate genset.  Think about it -- running two separate engines to do a job that can be handled by just one is usually not the most efficient solution.

The big Delcos on most of our coaches are rated for continuous output, and the heat is very efficiently removed by the oil supply, BTW.  I would not advocate this approach with a more conventional, air-cooled alternator, which often are not rated for this sort of duty.

-Sean
http://OurOdyssey.BlogSpot.com

Not to be critical but confused. I know an idling generator uses fuel, and as the load increases so does the use of fuel. Since I have been called anal I felt compelled to respond to questions about fuel use on a 20KW Kohler. I dry camped for about 170 hours two years ago. I camped 2 miles from the fuel station I topped off at so engine fuel consumption was minimal.

During the 170 hours I had 3 AC units running (daytime ambients were 90 plus), my HW heater, and my inverters. In the morning I ran the dryer to dry towels after my shower. I made coffee and in the evening I cooked on my Jenn-Air grille. The refrigerator (full size, double door) was always on. I have no clue as to my total KWH, but most of the time I saw about 30 amps per leg. I am sure that dropped in the evenings when I was asleep and outside temps were cooler. At the end of my week long stay I filled up at the exact same fuel stop (another 2 miles) and I took on 71 gallons, or an average of .41 GPH.

But like your measurements it is likely neither of us has the precision instruments necessary to obtain complete data, although my measurements of fuel purchased was as free of variables as possible since I used the same pump, the same nozzle setting and allowed the nozzle to click off and did not attempt to add more to the tank.

So my question is this........since energy is energy is energy can you explain how you can have a 10X difference in fuel consumption when there are similar efficiency losses due to both power sources being diesel powered. I always question representations of fuel mileage because I have recorded every single gallon of fuel added to my coaches for the 21 years I have had a coach and there are serious difficulties in measuring fuel efficiency because of variations in when the nozzle clicks off at various truck stops, speed, wind, use of parasitic loads such as over the road air, weight of the toad, hills, etc all have a distinct impact on fuel consumption. The most accurate way I have of fuel consumption reporting is my Detroit diesel Pro-Driver (which is subject to inputs from the operator) and by using 12 months of fuel consumption divided into the miles travelled.

KW can be converted to HP which can be converted into fuel consumption.

[luvrbus]

A FloScan will measure every drop of fuel that goes through the engine Cole has one on the supply and the return on his he knows to the ounce how much fuel goes into his 14L 60 series no matter where the  pump clicks off.

To me it was a expensive way to track fuel you had to pay for anyway

He had FloScans on his AquaHot it was so depressing to him he removed the Aqua/Hot lol

[TomC]

We have 160 amp Leece-Neville pad mount alternators for $160.00.  Delco makes the new 40SI alternator which is air cooled, brushless up to 270amp @ 12V.  But you could buy 10 of the above Leece-Nevilles for the price of one of the Delco 40SI's.  Good Luck, TomC

[Sean]

... fuel use on a 20KW Kohler ... an average of .41 GPH.

I am guessing your 20kW unit is turbocharged and at least electronically governed, if not actually a modern common-rail unit.  So probably a good deal more efficient, especially at lower loads, than my much older set, which is rated at over 1 GPH at half load.  I would guess most on this forum would see consumption numbers closer to mine.

But like your measurements it is likely neither of us has the precision instruments necessary to obtain complete data, although my measurements of fuel purchased was as free of variables as possible since I used the same pump, the same nozzle setting and allowed the nozzle to click off and did not attempt to add more to the tank.

Actually, my consumption measurements on the alternator are precise, because it is being measured by the DDEC, which knows exactly how much fuel is injected.  I have a switch that can isolate or connnect the house loads to the alternator, and so I can see exactly the effect at various loads and RPM.  Unfortunately, my display only goes to one decimal place, which is why I have to say 0.1-0.2 GPH.  It is probably close to 0.17 or so.  My genny numbers come from the nameplate ratings, which may be off by as much as 30% or so.

Even if we use your very efficient number, that's still about three times as much fuel for the same effect, not even counting the maintenance, which by my spreadsheet is about 10% of the per-hour cost of operating the genset at today's diesel prices.

So my question is this........since energy is energy is energy can you explain how you can have a 10X difference in fuel consumption when there are similar efficiency losses due to both power sources being diesel powered.

Yes, I can.  The very short answer is that efficiency losses are not linear.  If they were, then a generator with zero load on it would also use zero fuel -- clearly not true.

Put another way, there is a "base inefficiency" involved in running an internal combustion engine.  An engine with zero external load will still consume fuel.  An engine with half load does not consume only half the fuel of an engine with full load.  And so on.

Imagine for a moment that you have two identical 12kW generator sets.  Now further imagine that you have a pair of 100-watt light bulbs to power up.  You can run a single generator and put all 200 watts, or just 1.7% of capacity, on that generator, or you can run both generators and put each bulb on a separate unit, at just 0.8% of capacity.  Which one is more efficient?  Of course, running both generators to do this simple task instead of just one will use very nearly twice the fuel, and since maintenance is done based on hours, also twice the maintenance.  The same is going to be true for every pair of loads right up to full rated capacity of the generator -- running two 5kW loads on a single 10kW set will be more efficient than running those same two 5kW loads on two 10kW sets, or even two 5kW sets.

The math is very similar for having a large alternator on an already-running, already-loaded, already-hot main engine running well inside its power band vs. dropping that ~10hp from the main engine and instead running a whole separate engine to run perhaps 3-5kW of load.

...
KW can be converted to HP which can be converted into fuel consumption.

Uhh, no, not directly.  For example, 20kW is about 27 HP, but you can't run a 20kW genset with just a 27hp engine.  And the disparity between engine horsepower and electrical output varies with the capacity of the set.  Up to a point, the larger and more powerful the engine, the more efficient the generator set at rated load.   This is also the reason that the world's largest ships often use a single enormous diesel engine running a single propeller rather than multiple engines running either multiple props or some sort of multiple drive arrangement.  Likewise locomotives use a single large diesel generator rather than multiple smaller ones.

There are, indeed, good reasons to use multiple smaller engines rather than fewer larger ones.  For example, if the load is highly variable and engines can be shut down completely below a certain load, this might yield fuel savings.  Many ships and even pleasure boats have multiple generator sets of differing sizes, so that a smaller set can be used when the load does not warrant the larger one.  Some critical facilities have multiple identical generators to increase redundancy.  And sometimes, you just can't fit or perhaps transport larger units and so need to choose multiple smaller ones.  But none of that changes the baseline efficiency math for internal-combustion generator sets -- you are always better off combining loads onto a single larger engine than running multiple engines.

HTH,

-Sean
http://OurOdyssey.BlogSpot.com