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Old 06-08-2019, 06:52 PM   #1
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how much power can I draw from the alternator?

I have a 2002 39ft bluebird 8.1L gas V8 bus.

Got all the seats emptied except 4 and its about 2/3 full for my move 2000 miles cross country in a month or so.


as is obvious now I am moving at the worst possible time. july. yuck.


so. I Have 2 freezers and a fridge. 1 mini size freezer (looks like a 3cu/ft fridge but its a freezer) 1 chest freezer and 1 soda fridge. the 160can glass door fridge.


I also have a portable air con unit (8000btu IIRC)


SO. I have a 2000/3000w inverter. if I wire that booger up to the bus can the alternator handle that kind of draw? 20-22amps max typical probably 15amps. ?? usually its the engine that is the issue but I figure an 8.1L monster won't even sniff at that but will the alternator handle it ok?
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Old 06-08-2019, 07:17 PM   #2
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how much power can I draw from the alternator?

Iím interested in this this topic. As in what approximate percentage of maximum load is an alternator designed to handle.. I have a 240 amp one in my bus...

However I think your math is wrong 20 amp at 120 is (multiply the amps by ~11) is 220 amps at 12v....
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Old 06-08-2019, 07:18 PM   #3
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What exact alternator do you have?

Just one?

stock VR?

link to data sheet?
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Old 06-08-2019, 07:21 PM   #4
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Quote:
Originally Posted by Nerys View Post
I have a 2002 39ft bluebird 8.1L gas V8 bus
Looking for anything with that engine, leads appreciated.

Especially in a shorty, and would give my eye teeth for 4x4, prolly doesn't exist.
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Old 06-08-2019, 07:26 PM   #5
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what approximate percentage of maximum load is an alternator designed to handle
Depends on the alt, the VR and ambient temperatures.

The ones designed for Emergency responders can usually put out full rating all day if kept cool.

But maintaining voltage setpoint under higher temps or overcurrent demand requires converting to a fancy external VR, cost more than the alt.

DCDC chargers can substitute at lower currents.
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Old 06-08-2019, 07:26 PM   #6
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3000W at 13V = 230A
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Old 06-08-2019, 07:56 PM   #7
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Based on my non-scientific experience you can probably pull a continuous 80 amps @ 12V all day. Thatís about 1000 watts, and should run conventional fridges and freezers fine.

The AC unit would probably run fine by itself, but adding all the rest would make it marginal. More importantly, a little unit like that will do very little to cool you on the road.

Even if the inverter is rated for more, what size cables? Depending on the length of run you quickly need 2/0 or bigger to handle that kind of load. Research your application but IIRC #2 wire should be good for 80 amps if the run is kept short.

Could you push more? Maybe if all the correct precautions are taken, but I would aim for 1000 watts total and try not to ride past it.

Before I really knew what I was doing I ran a 1500 watt resistance heater off my inverter on a long drive in the dead of winter without issue, but cold weather is forgiving for cables and breakers.
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Old 06-08-2019, 08:00 PM   #8
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From what I have gleaned most of our busses came from the factory with 160-200 amp alternators (16-20 amps downstream of an inverter).

Two issues: there is often no way to know the spec you actually have, and no way to know for sure how to rate the duty cycle.

Thatís kind of where I got my 80 amps figure. 50% of the low end of the range should be fairly reliable.
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Old 06-08-2019, 08:15 PM   #9
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I run a 10.8 cf refrigerator (Energy Star) from a 1000 watt psw inverter. Based on my experience with that makes me think that running two or more may not play well. If two compressors kick on at the same time you are likely to overload the inverter. Not likely to hurt anything but the freezers will have no power until you reset it.

I considered something similar but my move was in late July and it was HOT. When I considered the cost and labor involved with installing an inverter to support my chest freezer versus the value of the food in it. I wound up giving the food away and move the freezer empty.

BTW: Buses make great moving trucks. We used two for our move. Maybe a little bit redneck.....
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Old 06-08-2019, 08:21 PM   #10
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DOLT. of course. thats why I should always use watts not amps.


full power to the inverter would be 144amps plus losses.


yeah. thats a lot. (2000watts/13.8v) 3000 is surge.


its a 496 engine with the allison lct2000 trans someone at a shop looked up the VIN for me.


IF its possible to run the AC cooling should not be a problem. I would only be cooling an area about the size of a minivan. the rest of the bus is "fully" packed to the ceiling. if its really bad I can use a genny to run the AC and inverter to run the fridge and freezers.


these are smaller units. They don't take much power. the AC is the real concern. the inverter is 2000watt 3000 surge. far far more than all 3 will consume. I am going to put a meter on them tomorrow just to get a better idea of just how much power they will slurp down.


I have a feeling you guys are right though. might not be able to use the AC. I know once its going it takes far less power so maybe I can cycle them. might not be worth the risk of damaging something. just weld a external shelf for the genny and use it to run the AC. so I will need another 2 gallons a day fuel for the AC. I can live with that.



for me the food is worth it. I already have the inverter and its an easy install. I get meats what not here for $1 per pound. just bought 30 pounds of center cut boneless pork chops $1 a pound !! Italian sweet sausage (nice large ones) $1 a pound. nice breakfast sausage 90c a pound. Butter $1 a pound. real butter!! wow. I tend to "stock up big" when I get prices like that. also have 500cans of canned goods in the buss. tuna green beans carrots wax beans fruits potatoes etc.. all 30 to 40 c a can. as best I can tell I can't get that where I am going. the longer I don't have to buy food the longer I can dedicate my funds to fixing up the **** hole of a house I am buying 1500sqft manufactured home sight unseen outside of pictures for $42k and I already know it needs $4800 for a new septic and about $6k for a new roof most likely. I can probably get away with a patch for a little while but once I goto do it I will just go with a premium metal roof so I will be dead before I have to deal with it again.


one thing is for sure. it won't be boring




as for moving truck buses. hell yes. best deal I could find was $4400 for truck trailer and insurance.


holy crap!


the biggest issue was the 12 days time limit for the rental truck. then $100 a day after. not possible. its taken me 3 months to get the bus loaded as much as it is now. it will take me 6 months or more to unload it on arrive (have to do it all by myself and it will be filled to the ceiling. every nook and cranny)



I bought this bus for $2800. and I can sell it on the other end making my moving cost minus fuel etc.. 0 or I can keep it and do something cool with it if finances permit me to.


I want to convert it into a mobile maker space. 3d printers computers laser cutters drills soldering stations etc..
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Old 06-08-2019, 10:11 PM   #11
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My 10 cu/ft fridge is 150 watts when running. It and the AC will have a significant start up load though.

Even though your space is small I would be surprised if the ac does much. The windows kill you with solar gain and the factory doors tend to be very drafty. I have a 12000 BTU that does very little. Iím in the process of installing a 30000BTU. I hope that keeps up a little better.

Whatever you do make sure the cabling that feeds the inverter is sized appropriately and has an matching breaker. Those high amp loads are no joke. You can weld or start a fire easy.
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Old 06-10-2019, 02:45 PM   #12
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yes. I will run a nice beefy cable. I already have cable that can handle 6KW. I have 97feet of it for my electric car and the new place won't need more than a few feet so I can use a couple of feet for the bus.


the fridge and freezers are a non issue. I metered them up yesterday. startup load for all 3 maxed at 900watts for about 30seconds then toggled around 600watts for a minute.


after that they never passed 180watts and only for a few seconds at a time idling at 75-80 watts for all 3.


about every 6-10 minutes they would bump up to 160-180 watts for 20-30 seconds then back down to 75ish watts.


so no concern their.


I have not put the AC unit on a meter yet. I will do that this week some time. IF it seems like I can run both on the alternator I will just start up sans AC until the coolers go into idle swap mode and then boot up the AC unit.


if that seems sketchy (last thing I want to do is cook the alternator or the VR then I will fab some sort of mount for the genny and run the AC off that after I confirm its worth even trying to do IE can it cool down the cabin or not. if not then well. I will just deal with the heat.


sadly I can't drive at night since its nearly impossible to get hotel rooms in the morning. have to wait till 2-3pm to get a room in most places.
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Old 06-27-2019, 05:06 PM   #13
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Forget the plan to run AC while freezers are running, travel while cool, insulate the freezers on the outside with blankets to reduce run time, put some dry ice in the freezers and keep the doors shut. The dry ice would probably be enough all by itself for a couple of days and just use the inverter for backup. Use low wattage fans with mister bottles to keep cool.


Only plug in AC (unplug freezers) when you absolutely can't take the heat. Its only temporary and no sense to spend a lot of time, $, & risk over loading equipment/alternator problems/fire for such a short time. You sure don't want to cause electrical problems for the bus



When I was a kid we didn't have AC, we were occasionally uncomfortable but survived just fine and so will you. Just a poor boys thoughts. Have fun with your trip.
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Old 06-27-2019, 05:28 PM   #14
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yes that is the conclusion I came to.


max output from the alternator is 1700 watts (and who knows if it can sustain that after 16 years)

more than enough for the fridge and freezers (even at full tilt they max at 900 but typically run at under 200 sustained)

even without the fridge/freezers running the AC would be closer to max safety rating of alternator than I want to risk.


yep. I had no ac as a kid either. but then I was a kid and not 42 years old beat up and over 400 pounds going 2000 miles on a 4 day trip


crap happens though. deal with it and move on.


one trick I have from my younger years though that I will institute. small ice filled cooler filled with rags. every now and then take out a nice cold wet rag and wipe down face head and neck. very very effective and gets all the grime and slime off you which is half the issue with heat and sweat.
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Old 06-27-2019, 07:02 PM   #15
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Quote:
Originally Posted by Nerys View Post
yes that is the conclusion I came to.

yep. I had no ac as a kid either. but then I was a kid and not 42 years old beat up and over 400 pounds going 2000 miles on a 4 day trip


.........gets all the grime and slime off you which is half the issue with heat and sweat.



I'm 68 yo and keep the house thermostat @ 88-90 in the summer, low 80's feels cold, high 80's feels good, 90's are ok, over 100 and I start looking for shade or an excuse to go into the A/C . Low humidity here in the desert helps a lot.


You are right about getting the "grime and slime off" makes you feel better in the heat. Mister bottle helps with that too, especially when you are trying to go to sleep.
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Old 06-27-2019, 08:48 PM   #16
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at 68 your are a less powerful thermal battery. its why older folks like the south florida etc..

I still generate a stupid amount of thermal energy (fat does not help)


but I am moving to new mexico (with the bus)


here in PA 80 feels like hell. 90 makes you want to curl up.


but in new mexico 80 will feel fantastic and 90 is just starting to get toasty just a little (15-20% humidity!!) and bonus 50's every night. (6600feet up and low humidity means the atmosphere does not hold heat like a thermal battery like it does here in PA where its 90 day time 85 night time


should be a ton more comfortable !!
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Old 06-27-2019, 09:08 PM   #17
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a little A/C isnt going to do much to cool a driving bus... 12000 BTI is like nothing compared to the fact brand new busses come wity 120,000 - 140,000 BTU of air conditioning.. insualting it helps... but seriously install road A/C for driving and use your small A/C for when parked...
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Old 06-27-2019, 09:44 PM   #18
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I think it would be more effective than you might think. in fact if I have time (Its not looking like I will) I want to try and externally mount my generator to run it. $6 a day would be worth it especially as I go through virginia tennasee and arkansas.

remember. the entire bus will be packed (to the ceiling) so I will only be cooling an area about the size of a minivan. I have used window units (little 5000btu units) to cool cars before it was more effective than I thought it would be (this of course depends on how hot and humid it is etc..) I did it just for shiggles because I saw pics on the internet of it and wanted to see if it would work

either way its not practical. max is 1700 watts and that was when new 16 years ago. I don't want to go past 60% capacity and would prefer to stay below 50% load on the alternator.


so no ac for me sadly its one of those. "I have the ac unit already" and "I have the inverter already" so it won't cost me anything can it work kind of deals.

Technically the alternator makes enough power. technically the wires can handle the load. technically the inverter has enough power 2200/3000)

I could also slap 600watts of solar on the roof to help soak up some of the load but I doubt I will have time to do either.


so not going to risk it. the cost of a break down because I burned up the alternator or worse something else electrical is just too great. so I won't risk it.

getting their intact is more important than being a little bit cooler plus I am getting a hotel room each night so AC bed shower sleep breakfast. that will help a lot. I have 3 days inn's lined up in cincinatti, little rock and amarillo. keeping each day to around 10 hours. playing it safe.
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Old 06-28-2019, 05:00 AM   #19
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One point to remember about alternators is that they put out max power at close to their max rotational speed. Most vehicle manufacturers will set up the alternator peak to correspond with the maximum rotational speed of the engine. At idle, you will not get the same power out of the alternator as you would at full rotational speed. Depending on the model of alternator, you may only get 40% of maximum at idle or low engine speed.


In your case, your data indicates you have a ~120A alternator. At idle it will put out about 50A, which is enough to run the chassis systems such as lights and relays. Your "house" power needs will be on top of the chassis needs and can cause you to draw from the batteries while idling. Of course, at cruise you may be able to recharge the batteries as long as the total load from your "house" needs and your chassis needs are totally met by the alternator output.
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Old 06-28-2019, 06:44 AM   #20
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Depends on the alternator. My Bosch sb200 iszrated to give me 200 amps at 2400 rpm that’s alternator rpm not engine rpm.. alternators have smaller pulleys therefore spin faster than the engine. It’s rated at 1200 to give me 140 amps. My pulley ratio is pretty steep , 2.5:1 I think. At 600 engine rpm my alternator is spinning at 1500.

Each one has a output to rpm chart. Some electronic regulated alternators willl reduce voltage if they get too hot.
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