My friends Ford F-450 came with a 200 Amp x 14 Volt = 2,800 Watt alternator.
Still running strong
1,440 Watts would only be a 50% load.

Typically 35-60 amps on a truck is normal key on engine running with two good batteries and normal loads. 100A+ the normal 35A-60A....It will be an Achilles's heel over time. Most ambulances' run duel alternators for similar reasons. Im guessing the original poster has a 5.9 Cummins powered motor home...it can be set up for duel alternators. Just trying to help.
-Jason

 

Isolator is rated to 225A

 

Engine is a 6.7 Cummins. Second alternator is an option, albeit a challenging one. It's a rear radiator setup and there is VERY little room between the radiator shroud and the rearward facing engine. Getting to the belt that is there is a PITA..... Increasing the belt size to ADD the second alternator would be a challenge. Plus, I don't know that it would do to the other components re belt angle and contact surface. Adding a pulley on the crankshaft to run a second belt just for the second alternator would be even more of a challenge.

Good news is that there is a very large fan in said shroud. Standing behind the thing when that fan kicks into high speed will send your toupet into the next county. I am cautiously optimistic that there's enough air flow to keep the alternator cool, as it is upstream of all this.

Maybe adding a temp probe could be part of my data gathering.

 

Generally speaking, alternators are spec'd out to approximately 80% of their maximum output. I don't think adding roof air into your system is the way to go but if you decide to, I would maybe be looking upwards of a 300 amp alternator as a good buffer. On top of that, you need to change the wiring to accommodate the extra amperage. If you are running high amperage you really need to consider airflow past the alternator because diodes don't like the heat you are going to produce and if they are not kept cool, they will be first to go. The best bet would be to run dual alternators as mentioned earlier, but everything in the system needs to be balanced so that one alternator is not doing more work than the other. That can be expensive as well but it will run cooler and be more efficient over the long run. Losing one alternator temporarily will not leave you stranded. I would give this some good long thought. If it was that easy, everyone would do it. If you are going to 300+ amps, look for firetruck or ambulance alternators from Leece Neville or Prestolite. They are made for that type of work. Buy from known good rebuilders.

 

If it was that easy, everyone would do it.

Actually, many people are doing it, and 300A would be overkill. I suspect I'll need about 170A so with your 80% rule that's a 215A alternator.... The 200A is a straight swap.... but I'd like a little more. 240-250 would be perfect.

Yes, cooling is a consideration. As mentioned before, there's a very large fan creating a LOT of air flow in that compartment, coming up from the street and going back. The alternator is pretty early in the flow, so will be getting a lot of air which should be close to ambient. Of course we're running air when it's hot out.....

I think a temp probe will be in order too....

 

I used to be a rebuilder at one time and did all kind of custom work. I said 300 because I know you are going to haveall kinds of room to let that unit run cool. Bigger diodes, heat sinks etc will give you room for trouble. Diesels draw more amperage on startup, sulfated batteries etc drive running amperage up. I live in Canada and when it gets cold, we put high demands on our equipmemt. Hence the overkill. You can probably get away with 250 and have a decent buffer zone. I dont doubt more people are doing it. I just dont see that part of the business anymore. Good luck. Hope it goes well.

 

Greetings,

New to this forum, not new to fora.

The application is a motorhome. Diesel engine with alternator. Two lead acid battery banks ("house" and "chassis") with intelligent battery isolation manager which parallels the banks when there's a charge source on either and the other needs charging. Smart 120V AC powered battery charger.

Condition is while driving and in need of AC. There's an automotive style dash AC which keeps the cockpit cool, the house behind it has two roof mounted 120V AC's. Currently the only power source is the on-board diesel powered 6000W AC generator. Running this for just a 1500-2000W load for all the hours of driving is not the most efficient.

My objective, and there is precedent, is to run one of the roof AC's through the 3000W pure sine inverter from the house bank (450Ah total). Keeping it charged would be on the alternator. Current alternator size is 160A. This would need to be increased. A 200A alternator of the same model is a direct swap out. According to the manufacturer (Delco Remy) it is suitable for continuous duty at or near it's rated output, provided it gets adequate cooling.

This may or may not be enough. The AC load would be 12A 120VAC, 1440W = 120A 12VDC. The chassis has a DC load to run. How much I don't know.

Here's the question (yup, there is one).....

The FIRST thing I want to do is measure, real time, the output of the alternator as currently installed. I need a DC ammeter rated to around 300A that can be installed in the POSITIVE output of the alternator, with a readout 40 feet away...(rear engine setup).. I would like something that I can permanently install in/on the dash. So far everything I have found needs to be in the negative cable to a battery, but this is not practical as there is output going from the alternator to multiple locations. I need the actual output at the ALTERNATOR. Second problem is that a twisted pair to a shunt would travel the 40 feet to a readout and be subject to all kinds of interference.

Suggestions? Thank you!

Purchase a suitable shunt on ebay. Many show 75 mv at rated current. Use a voltmeter to measure the current and calculate the current using Ohms Law. As both the voltage and current are low, any good quality wire that can stand the engine heat will work.
I've got several to measure starter draw.

 

I have used shunts in the positive lead with no problems at all. There are cautions to be taken, and it is smart to put a low current, say 1 amp, fuse in both leads to the remote ammeter, for protection in case of an accidental grounding. Use a shunt that will work with your selected meter. A digital meter will be a challenge if the input must be isolated from the power circuit, and that might be a big pain. So use a small AC operated supply fed by the ac inverter to power the meter.. 1 extra watt will not matter.

 

I don't know much about A/C, but would it be feasible to upgrade the compressor so it could cool the whole motorhome? More expensive up front, but there'd be fuel savings due to greater efficiency, and maybe longer service life. Just throwing that idea out there...

 

Along with the compressor one would need a larger set of coils and a larger air distribution/circulation system.

Edit: As for efficiency, insulate and seal motor home.

 

For a temporary setup to measure the alternator current just use a small battery to power the digital meter. Not for a permanent setup but it will be fine for an hour's worth of checking. But be sure to use adequate wires to connect the shunt to the alternator.
But by this time you may have already done the check.