Charging batteries with the engine

[Redram99]

Hi all.

I have a 2011 triple e senator 25d. Great motor home. E450 v10.

Just curious, what is the output of the alternator vs the standard converter?

It seems to charge the house batteries off the engine alternator very quickly.
Would that be nearly as economical as running a 4000 Onan?

Thanks.

[Oldtymeflyr]

Depending on the state of charge of the battery, it will take hours to charge a battery with an engine idling at say 750 rpm. Even a half charged battery will take hours to properly charge, that is to bring it to as similar state of charge after a days travel on the road.

At idle approximately 750 rpm, an alternator is barely making enough power for mandatory equipment, ie. EFI fuel pump, the engine managment system, the electrically controlled fuel injectors, etc. and some to the battery of the vehicle. Boost the idle up to fast idle about 1800 rpm, and there is more going to the batteries. I would not like to "idle" a Ford V10 at 1800 rpm for hours.

Alternators are rated at 6000 rpm, alternator shaft speed, approximately cruise speed for the vehicle. At slower speeds, alternator output really drops off.

The more batteries being charged by an alternator the more heat and wear on that alternator and its just not good for an engine to idle for hours, there can be build up of deposits, a lightly loaded engine can "make oil". The cost of replacing a Ford V10 is probably between $5000 and $7000. With new accessories maybe more. I am sure that there are people who can do it for less.

We have a generator and do not charge the batteries with the generator, its the same thing, it takes hours to properly charge a battery.

Best solution is be on the grid or go with solar.


Good Luck.

[time2roll]

Redram99 wrote:
Just curious, what is the output of the alternator vs the standard converter?

It seems to charge the house batteries off the engine alternator very quickly.
Would that be nearly as economical as running a 4000 Onan?

Thanks.

typically the alternator will have more amps and more volts. But it has the chassis to run and the wire to the house battery can be long and restrictive.

If the house battery seems to charge fast on the alternator you should be in good shape with the system working as designed. However it may just seem fast because the converter is slow. Many or most converters charge at a 13.6 trickle voltage and take 8 to 24 hours to fully charge a low battery.

Alternator will always win on efficiency while in motion. While at camp the Onan should be better but depends on the converter supplying the proper voltage.

Post the converter model number for best suggestions.

[Desert_Captain]

One of the many advantages of a large gasser vs the Mercedes {or other diesel} is the ability to let the gasser idle for extended periods of time. {Don't even think about trying this with a diesel}. :S

I have only availed myself of this feature twice, once to run the dash AC when the roof unit was overpowered by the heat and humidity in an Illinois cornfield {where our small RV park was located}. This kept us cool and comfortable while we waited and hopefully were missed by the multiple nearby tornadoes {a very long and spooky afternoon}. :E

The second time my aging house bank ran down due largely to a lot of furnace run time overnight and the generator would not start. I just let the V-10 idle for an hour and this recharged the house bank more than enough to fire up the genny. Yes, when I got home I replaced the 4-year-old house lank {2 group 27 true deep cycles}.

Our 2012 Nexus only has 81 hours on the generator despite having 48,000+ miles. This is due largely to the fact that my house bank is more than capable of sustaining us for 3 or even 4 days. Like most folks we just don't use much DC power. Our typical pattern is to stay no more than that at any one location. Driving for just a few hours to our next stop inevitably recharges our house bank to nearly full and the cycle begins anew.

Most of the time I end up running the genny not because I lack power but to exercise it. I always make sure to put a serious load {AC, water heater etc} for an hour on the genny when doing so. Works for me.

:C

[theoldwizard1]

If you are simply recharging your house batteries, current (amps) DOE NOT MATTER MUCH (unless you are in a hurry to put a big bulk charge into your house batteries).

The MOST important thing is HOW MUCH VOLTAGE IS RECEIVED AT THE HOUSE BATTERY CONNECTION ! More amps does NOT help this issue. On most vehicles, there is NOTHING you can do to a standard charging system that will really help. Larger wire helps a little.

The bottom line, YOU WILL NEVER BE ABLE TO COMPLETELY RECHARGE A HOUSE BATTERY BANK BE HOOKING IT UP TO A VEHICLE CHARGING SYSTEM !

[pianotuna]

The alternator is most probably 130 amps. Duty cycle is 1/3 of that.

Two solutions:

Add a 2nd alternator dedicated to house duties

Add an external diode so the "brains" of the engine do not control output for the house jars.

[Lwiddis]

Starting a vehicle engine to charge house batteries should be a last resort option. Starting a generator to charge house batteries on a sunny day is also not the best option...try solar. Works sun up to sun down whether you’re in camp or out exploring.

[BillHoughton]

Hard to imagine that an engine rated to run a multi-ton vehicle down the road, using a fraction of its power to run an alternator while wasting the rest just turning itself over, could be more economical than a generator on which the engine is sized to the power needs of the electrical generator attached to it.

[DrewE]

On my class C, the alternator seems to charge the house battery a little bit faster than the converter. It has nice heavy (2 gauge or so I think) wire between the house and chassis battery. It really boils down to which charge source can maintain a higher voltage at the house battery, which in turn depends on the converter (multistage vs. single stage), the voltage regulator for the chassis, the alternator's capacity, the voltage drop of the wiring, etc.

I the generator, none the less, rather than starting the main engine. It's not really great for an engine to idle for long periods, and it's sometimes useful to have AC power for other things besides just charging the house battery.

Of course, if you have need of driving somewhere anyhow, it's a no-brainer: don't bother with the generator.

[BFL13]

Redram99 wrote:
Hi all.

I have a 2011 triple e senator 25d. Great motor home. E450 v10.

Just curious, what is the output of the alternator vs the standard converter?

It seems to charge the house batteries off the engine alternator very quickly.
Would that be nearly as economical as running a 4000 Onan?

Thanks.

You must be thinking the quick rise in voltage means they are charged up. In fact that is just the beginning of getting them charged up, which can take hours "depending".

You need a battery monitor to tell what is going on while they are being charged. After you stop the charging, and they have no loads on them either for a while, then you can take their voltage and get an idea of their state of charge ("resting voltage")

The alternator amps to the battery will be reduced by the usual thin wire back to the battery and also from the way the voltage regulator for the alternator works wrt the engine battery. MHs are not all the same, but eg, ours gets about 25 amps to the house battery bank once thing settle from the initial start (takes about five minutes to settle) while the converter can do twice that. The converter only works off shore power or generator, so alternator charging while driving is a good bonus feature.

[JaxDad]

The rated output of the alternator is just one factor, the speed at which the alternator turns makes a huge difference also.

Under SAE J56 standards the ‘rated’ output of the alternator is at 6,000 RPM.

Most automotive alternators are designed to give a pretty solid output at about 2,000 RPM but don’t give much current at idle.

[valhalla360]

Depends, if it has a high output alternator.

If you have just a standard alternator most likely running the charger off the generator will be faster.

If you have a big 300amp continuous output alternator (most automotive alternators put out the rated amount for a short period to replace the motor starting draw then drop way back), it can probably do it faster.

Of course if you are driving anyway, take the free charging.