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Author Topic: keep 24 Volt? or go 12V  (Read 2010 times)
robertglines1
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« on: September 30, 2013, 04:28:39 AM »

On the 98 prevost rebuild :;I find I have not much need for any 24 volt at all.  A few gauges.  The ac motors are gone.  The starter is 12 volt. the truck alternator is 12 volt. I have 12 volt defroster fans,wiper motor.  The headlights are 12 volt. I'm replacing all the clearance lights with 12 volt. The DDEC IV is 12 volt .The level low has 12 volt coils. The fuel gauge is a problem I ask about on a separate post and I don't know about tach. All gauge sensor are from DDEC IV......  Can anyone think of a reason to keep a dual electrical system?     Bob
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bevans6
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« Reply #1 on: September 30, 2013, 04:50:10 AM »

All I can think of is to run the inverter.  12V inverters need those big cables for decent power, and 3000 watts is about as big as a 12V inverter comes.  24V makes more sense if you need high power.  The battery requirement is the same.  You can stack 2000  or 3000 watt inverters to get more power if needed.  I don't think I would run a 24V system just for the inverter, to be honest.  The whole point of why a bus would have had a 24V system in the first place comes down to running the OTR AC fan motors, that is about it.  If it wasn't for that high power application buses would have 12V systems just like trucks do.  The inverter is our equivalent of the OTR AC load.

Brian
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« Reply #2 on: September 30, 2013, 07:27:07 AM »

The DDEC doesn't care if it is 12v or 24v only the 1 and 11 DDEC  were volt sensitive 
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TomC
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« Reply #3 on: September 30, 2013, 08:04:19 AM »

Coming from my own experience with a 12v bus, go for it. Having all 12v is much easier. Virtually all over the road trucks are also 12v (no more 24v starters with a series/parallel switch). Good Luck, TomC
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« Reply #4 on: September 30, 2013, 06:24:52 PM »

In years past people on this board would be jumping up and down telling you how great and more efficient a 24v system is in a bus.  I always took the other position-- 12v is the way to go for house and bus systems.  I only have the starter and and a few relays that are 24v, so I have a 160 amp 12v alternator and a 42 amp 24v alternator to contend with.  NO gear driven 300 amp 24v alternator to blow up and take the engine out.

--Geoff
« Last Edit: September 30, 2013, 06:31:04 PM by Geoff » Logged

Geoff
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« Reply #5 on: October 01, 2013, 03:50:09 AM »

If you replace the 24 volt bulbs with the same wattage 12 volt bulbs the amperage draw will double. Is the wiring size adequate?   

Ken
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robertglines1
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« Reply #6 on: October 01, 2013, 04:36:47 AM »

I will check clearance lights for voltage(only thing I haven't checked yet). Wires look to be at least 18ga maybe 16 ga-- might just go led.  good point!!  Feed harness is at lest 12 ga---I had to replace part of it due to the fire. All the other tail light etc are 12 volt in this coach already.   Always need help thinking things thru/check signals..  Thanks    Bob
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« Reply #7 on: October 01, 2013, 06:46:11 AM »

So not to hyjack the post but as I only have small 24 volt draw and the 24 volt heater motor for the bus heat that I hardly use . How much power does the 300 amp. dn 50 alt.  use and what about 1 @12 volt alt 140 amp , 1 @ 24 volt alt 85 - 120 amp looks like a better set up    thanks    dave
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« Reply #8 on: October 01, 2013, 07:52:53 AM »

Bob I would go LED lights and not worry about the 24V!
Grin  BK  Grin
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« Reply #9 on: October 01, 2013, 07:55:36 AM »

Whether the alternator is 300 amp or 30 amp, it only uses the power you take out of it.
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robertglines1
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« Reply #10 on: October 01, 2013, 09:15:27 AM »

Everything but clearance has been changed over to 12 v led already. Just forgot about them till Ken jogged my gray matter.  Needs a little shake once and awhile.   Bob
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« Reply #11 on: October 01, 2013, 09:52:39 AM »

How much power an alternator takes to drive is based on the wattage output, the drive type, the cooling fan (if any) and it's efficiency.  A 50DN takes very little to spin it if it's turned off, it's got good bearings.  It's probably in the 50% to 60% efficient range, so if one HP is 750 watts(ish) then you might get 400 watts out for every HP in.  If it's belt drive, figure 15% loss, if it's gear drive figure 30% loss, so 340 watts or 280 watts per hp.  If it has a cooling fan, figure another 15% for it.  You will probably get around 340 watts per hp for a belt driven oil cooled 50DN, 280 watts per HP for a gear drive oil cooled and around 250 watts per hp for an air cooled 50DN gear drive.  You get the picture.  Based on my instance, belt driven oil cooled, and pulling 2,000 watts to run my inverter powering my rooftop AC, I would figure a little under 6 HP.  That is around 72 amps at 28 volts continuous.  The thing is, any alternator is going to be very close to the same numbers for the same power output.  A modern brushless might be 60% to 70% efficient (Like the Delco in this thread) but it's belt drive, air cooled fan, and will pull the same rough power out of the engine to drive it.  Four drive belts is a little less efficient than two, depending on belt size and such.  The modern toothed drive belts can transfer a lot of power and are very efficient compared to the old heavy vee-belts.

Brian
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« Reply #12 on: October 01, 2013, 05:03:35 PM »

I easily run one 1500 BTU roof AC off my 160 amp, belt driven alternator.  According to my Trace inverter it is only pulling 8-9 AC amps at 120v.  I made a plate to cover up the hole in the flywheel housing where the gear-driven 24v 50DN was.  No more restless nights and days wondering if the 50DN would blow up and take out my gear train.

It's sitting on the floor of my shop with the regulator.  Any offers?
« Last Edit: October 01, 2013, 06:02:50 PM by Geoff » Logged

Geoff
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« Reply #13 on: October 02, 2013, 08:59:34 AM »

How often do the 50dn alt. granade and is there a warning to look for b 4 hand ?

thanks    dave
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« Reply #14 on: October 02, 2013, 09:14:40 AM »

Geoff opened a can of worms here lol you need to remove the 50D every 100,000 miles and check the alternator bearing and the gear alignment on the cam  it is not a easy task but it needs to be done they give no warning and when one goes it destroys a engine you save the block and crankshaft if you are lucky the rest is history  

The nut that holds the gear on is bad about coming loose if it hasn't been locked in someway I center punch the the shaft on the edge to prevent that from happening  fwiw

Some here say it never happens but it does I have rebuilt few engines because of a 50D I would not have one on my engine just like Geoff when you shut the engine down they backlash and it will take a toll in time JMO about a gear driven 50D YMMD

good luck
« Last Edit: October 02, 2013, 09:26:13 AM by luvrbus » Logged

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« Reply #15 on: October 02, 2013, 09:24:57 AM »

You should qualify those statements to make it clear you are only talking about gear driven 50DN's. 
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« Reply #16 on: October 02, 2013, 09:30:11 AM »

It applies to all gear driven alternator or generators Cat had no luck with a gear driven charging system either belts are the way to go all they do burn off and slip that doesn't happen with gears
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« Reply #17 on: October 02, 2013, 09:31:20 AM »

As I understand it, the alternator is fine but the planetary gear drive that steps up the speed from the cam-shaft is what wears, gets out of alignment, and causes problems.  I wouldn't have one, either, just based on not having the special tools to set it up and maintain it properly.  If you are interested, it's in this section of the MC-9 manual  http://www.buses101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%207.pdf

Brian
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« Reply #18 on: October 02, 2013, 09:43:39 AM »

So its all Geoff's fault that I have to look for a new 24 v alt. ha! ha!

Now with only having the 24v  bus blower motor ( heat ) and the vanner 50 amp  how large of a 24 v alt. should I need and were do I find one ?  
 thanks   dave
« Last Edit: October 02, 2013, 11:47:00 AM by sledhead » Logged

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« Reply #19 on: October 02, 2013, 09:45:23 AM »

They will break the cam shaft also even the special cams made for the 50D Don Fairchild is always looking for that cam for the 8v92 if it was not a problem DD would not make a special cam to drive the 50D
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« Reply #20 on: October 02, 2013, 10:37:11 AM »

I talk to busnuts all the time who blissfully truck on down the road with gear driven 50DN's and have no clue about the miles that are on them.  They get a little nervous when I explain the ramifications of no maintenance.  We operated a lot of them, millions of combined miles and never had a failure, but.....we rebuilt each and every one ourselves at between 75-100K miles, way cheaper than an engine.   This consisted of a Kirk's Automotive kit with the big bearings, genuine Delco-Remy diodes, new insulators, the whole bit.  Bearing material going through the gear train will certainly wipe out the whole engine, bent valves, cracked heads, the works.  On older MCI's many 50D's were driven through an alternator adaptor.  Detroit Diesel would not allow MCI to bolt the alt directly to the engine (when GM was building buses) so the adaptor had to be used.  This added another dimension of possible failure, the adaptor bearings.  And, the weight of the big alternator plus the adaptor jumping around on the back of the engine required the support bracket be used.  If you don't have one guys, get one and put it on.  Typical prices I hear to overhaul 50D's are around $1,000.  Back then, our overhaul kits were around 300.00, and it took us about 6 hrs to do the complete job.  For shade tree mechanics that want to do this job a special alignment tool is a requirement for installation and the tool is expensive.
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« Reply #21 on: October 02, 2013, 10:51:28 AM »

Dave- We have a 45 amp, 24v, single wire alternator.  The vehicle electrical is all 24v; that's really only lights, driver's heater, and various accessories as well as charging the batteries, of course.  The alternator seems to be more than enough.  They must be available online or an auto electric shop should be able to build one.
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« Reply #22 on: October 02, 2013, 11:09:34 AM »

Yep Boomer, Kent/Moore was very proud of the J 29893 tool to setup the 50D on the DD engines
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« Reply #23 on: October 02, 2013, 11:56:53 AM »

So its all Geoff's fault that I have to look for a new 24 v alt. ha! ha!

Now with only having the 24v  bus blower motor ( heat ) and the warner 50 amp  how large of a 24 v alt. should I need and were do I find one ? 
 thanks   dave

The 24V bus evaporator/heater motor (in my MC-5C, your is probably similar) is around 1.5 hp.  The condenser fan motor is 2 hp, but you probably don't have it any more.  1.5 hp, including efficiency losses, is probably around 1500 watts, or 55 amps at 28 volts.  Assume triple to start, but the batteries supply that.  It's breaker is 80 amps, so that tracks.  Add in your 50 amp warner (which I have no idea what that is), and you are at around 105 amps.  Automotive alternators (like the ones on trucks, etc) you figure 50% of rated maximum for continuous, so you would want a 210 amp rated alternator, which you would probably have to spin at 6,000 rpm (to figure your pulley ratios).  That is, quite frankly, a honking big 28 volt alternator, the 50DN originally in my bus was rated at 235 amps, but it could run at that rating for a long time.  There are big alternators that can run close to maximum output continuously, but they are about as big and costly as the 50DN, in that ballpark anyway.

So bottom line, the factory OEM climate control is what the big alternator was for, and by retaining the factory heater motor you still have half that system in place, so you still need a pretty big alternator.  I think there are 200 amp 28 volt choices around.  You can run two 125 amp units in parallel, that works fine usually.  The factory belt drive setup on the MC-5C has a four sheave pulley, you could really easily run two belts each to a pair of alternators and mount them where the factory 50DN was, if you could find one of those pulley drive assemblies.  It would be redundant too.

Brian
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« Reply #24 on: October 02, 2013, 12:20:27 PM »

Geoff's system of running two alternators off the transmission A/C drive is a good one-that is if you have the gears inside the transmission to use. My bus was a Portland, Or bus without A/C-hence I do not have the inside gears for the A/C PTO. I still use my gear driven 50DN. I had it rebuilt about 4 years ago. Not had any problems with it. You could replace the gear drive with a pulley setup. Good Luck, TomC
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« Reply #25 on: October 02, 2013, 12:33:19 PM »

I just priced out a new 12v 145 amp. 1 wire for $140 + $30 core charge =$ 170

24 v 70 amp 1 wire for $ 253 + $35 core charge = $ 288

I have the org. lower pully for the a/c and will build a mount to run off that
 thanks    dave
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