| Author | Message | ||
| ron and patti (Hayleyscomet)
Rating: |
We are changing our 11.1 series 60 (350 hp) to a 12.7 with 500 hp. Our 11.1 had a 270 amp oil cooled alternator, which we intend to swap over to our 12.7 but have been told that this alternator is a horse power hog, and we should consider replacing it with a smaller one. (we kept the over the road air). Does anyone have any thoughts on this or know how much hp these big ones use? Thanks for your help, Patti | ||
| RJ Long (Rjlong)
Rating: N/A |
Patti & Ron - Think about it for a moment. . . You're going from 350 hp to 500 hp and you're worried about the hp drain on the engine from the alternator? That 500 hp engine won't even notice the alternator on it. Plus, you need the monster to operate that over the road a/c system.  RJ PD4106-2784 Fresno CA | ||
| Sojourner (Jjimage)
Rating: N/A |
Amen RJ! 270 amps is a blessing to have for running roof or central or split. Caution if engine’s oil temp is higher then 250º F during heavy charging & hot-day driving, then add an oil cooler w/ electric fan. Or water-cool-oil exchanger if enough reserve engine’s cooling capacity available. FWIW Sojourn for Christ, Jerry | ||
| Sammy (Sammy)
Rating: N/A |
Leave it alone.Swap it over.Don't worry about it. Detroit Diesel had an update to the top vent line for that alternator. Now it has a #6 line for better oil return, flow.If yours still has the piece of #4 line, consider the update kit. Not a big deal, very simple installation. Enjoy your new 12.7. | ||
| Stephen Fessenden (Sffess)
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The horsepower used by the alternator is going to be proportional to the power produced (amps). If you are running a 70 Amp alternator it will use approximately the same horsepower as the 270 Amp alternator will when it is only producing 70 amps. It is the job of the voltage regulator to tell it how much to put out. With no output neither uses much power. You will either use a 5 hp X 10 hours to charge the batteries for 10 hours or 50 HP for one hour to charge them in one hour. Same energy cost, except you have a choice of running the engine a shorter time to accomplish the same thing. | ||
| FAST FRED Rating: N/A |
"You will either use a 5 hp X 10 hours to charge the batteries for 10 hours or 50 HP for one hour to charge them in one hour." But not with the stock V regulator. Short recharge times ONLY come from a smart 3 or 4 stage V regulator with a battery temp sensor. FAST FRED | ||
| Marc Bourget Rating: N/A |
Augmenting a point made above for the benefit of newby's or those not exposed to the proper care and feeding of batts (Much more than meets the eye with this stuff! - Enough that I should refer to notes first . . . the following is "off the cuff"). It's my understanding that Steve's position on charging rates (5 x 10 or 50 x 1) is valid only when the battery bank is of sufficient size. The maximum absorbtion rate varies between regular lead-acid, AGM and Gel Batts (etc. The chemistry, internal plate structure and the materials used to keep the plates separate all play a factor). IIRC, the optimum rate for lead-acid, on bulk charging (first stage of the 3 Stage charging profile provided by the regulator mentioned by FF) is in the range of 20-25% of the overall Amp Hour capacity of the bank. Some high quality batts on the Euro standard are significantly higher. | ||
| Jerry Liebler (Jerry_liebler)
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Marc, You've hit on a good reason to avoid switching from 8D to group 31 batterys for starting in a 24 volt bus. Lead acid batterys are usually rated for a max charge rate that is the amp hour number ie. 1 hour charge. With 8Ds 270 amps would never be exessive but with the group 31s it would. However the chances of ever actually having all 270 amps flowing into the batteries would be very small. Regards Jerry 4107 1120 | ||
| Richard Bowyer (Drivingmisslazy)
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Jerry, and if it actually did accept this much current it would only for a very short period of time. Never long enough to do any damage. The internal impedance would quickly limit the current to an acceptable range. Richard | ||
| Buswarrior (Buswarrior)
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Hello Patti and Ron. It has been generally suggested that the entire needs on a stock coach HVAC are somewhere around 25 HP to drive the AC compressor and the alternator to run all the fans. As noted by those posters above, if the big alternator is being a power hog, it is making big power, that you want, and need! Otherwise, it's just back there loafing, like any other alternator. I expect that you are quickly learning to be suspicious of advice you recieve from well meaning people! happy coaching! buswarrior | ||
| ron and patti (Hayleyscomet)
Rating: N/A |
Thanks for all your advice. We'll be keeping the big alternator. Patti |
