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Author Topic: 64 Prevost, NEED (not want) custom cooling!  (Read 4627 times)
RoyJ
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« on: June 01, 2010, 06:47:58 PM »

Hi guys,

New member here. Been dreaming about owning a bus since a kid (not that long ago! at 24, wonder if I'm the youngest bus owner here? Cool). Origionally planned on saving up for 10 years or so and get a 90's Prevost with hopefully a S60 engine, but came across this deal that I couldn't refuse, and can afford right now.

So I got myself a 1964 Prevost, which no one can figure out the model, with a 6V71 and Spicer (I think) 5 spd manual. To my surprise, I have 4 valve heads and N70 injectors, so I'm estimating my hp at 240. It's a 35' highway coach, and for the age, just about perfect inside out, and drivetrain wise.


So, now, the problem. For the past twenty years the bus had an electric cooling system. I've read just about every thread regarding this topic, and realize there has been some pretty heated discussion regarding the inability of electric fans to cool a bus. And I believe most of what has been said. I'm a Mechanical Engineer, and my last job at Daimler was fuel cell design. Fuel cells would make typical 2 stroke heatloads look like a lawn mower  Grin (we're talking 50+% heat rejection here!)

I think this bus got lucky because 1, it's a 6V71 with relatively lower heat rejection, 2, it's got a manual transmission, and 3, it has big tanks and a big rad mister! So somehow, this bus made through 20 annual summer trips from British Columbia to Mexico (through Arizona).

But the radiator now needs a replacement, as the fins have rotted. It's on the small side as far as buses go - about 24" x 24" and 3" thick. It's currently cooled by 4 fans off old VW Bugs mounted on a custom made shroud. I realize it's no match for the engine driven OEM fan. But, the chances of finding a engine driven fan that fits my bus is slim to none, so unfortunately, I have no choice but to stick with electric. However, I do want to improve on the old setup.

What I'm guessing is that electric fans can blow a lot of CFM, but without the hp to back it up, they can't do so WHILE maintaining useful static pressure. Couple that to the thick radiator used on coaches, and you can smell (literally!) disaster. So here are two of my plans so far:


1) use two heavy duty pickup radiators. Typical measurement is 17" by 33" each, so a total of over 1000 sqin surface area. Flex-a-lite makes a "heavy duty" cooling fan and shroud system, consisting of dual 15" fans. In total, I'd have 4 15" fans (better than 4 10" fans now), but blowing through much less restriction, as the radiator is only 1.4" thick. The radiators will be connected in parallel to maintain higher water flow.

Problem: the Flex-a-lite fans are $550 for each rad, and from searching old posts, I realize their engineers don't even test their fans! So I feel getting ripped off paying $1100 for some fancy plastic work!


2) Get the rad re-cored to origional standard, and use a engine driven fan blade. The bus has dual alternators, I will change one so that it's full fielded, and therefore generate roughly 120V DC at full engine RPM. This is a cheap trick to get huge horsepower out of a ordinary alternator. With my 100amp model, I have the potential to generate 12kw, or 16hp! This will allow me to power universal motors found on power tools. I'm thinking of two 15 amp motors off a circular saw, which are geared for 5800 rpm.

Two such motors will produce 4 horsepower peak, and drive a fan enough for 95% of conditions.



I'll stop before this turns into a novel. What are everyone's opinion on this?

Thanks in advance.


Roy
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luvrbus
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« Reply #1 on: June 01, 2010, 07:22:36 PM »

Roy, did you buy the one that was listed on Maritime RV that is a nice looking bus if you did



good luck
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Len Silva
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« Reply #2 on: June 01, 2010, 07:33:26 PM »

I'm not familiar with that bus but I can offer a couple of thoughts for your consideration. 

It sounds like the cooling system was woefully inadequate, thus the large misting system thus ultimately the most likely reason the radiators are in such bad shape.

Misters are a band-aid, not a solution.

Universal motors are not designed for continuous service, and will not survive very long. 

I would strongly suggest a mechanical or hydraulic engine driven fan for cooling and using a full size heavy truck or bus radiator.
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« Reply #3 on: June 01, 2010, 07:37:25 PM »

Welcome, nice way of describing your plans, well understood. I would go with option # 2. I believe when one starts modifying with such things as rads you may very well run into a restriction issue. Sure others will chime in.
Grant
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RoyJ
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« Reply #4 on: June 01, 2010, 07:55:07 PM »

Roy, did you buy the one that was listed on Maritime RV that is a nice looking bus if you did



good luck

I haven't seen that ad, but I highly doubt it's the same bus.

Bought it from a local guy here in BC, Canada. Got it for $10k, which compared to the stick and staples trailers I was looking at, seems like a steal (so far, hope no surprises will pop up!).
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RoyJ
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« Reply #5 on: June 01, 2010, 08:03:36 PM »

I'm not familiar with that bus but I can offer a couple of thoughts for your consideration. 

It sounds like the cooling system was woefully inadequate, thus the large misting system thus ultimately the most likely reason the radiators are in such bad shape.

Misters are a band-aid, not a solution.

Universal motors are not designed for continuous service, and will not survive very long. 

I would strongly suggest a mechanical or hydraulic engine driven fan for cooling and using a full size heavy truck or bus radiator.



I agree about the inadequacy, which is why I'm surprised it made it this long.

Thanks for warning me about the universal motor duty cycle thing. This is one of the things I'm afraid of. Although, most mountain grades in my area at no more than a 5 - 10 minute climb, which seems to be within limits of commercial strength power tools (heavy duty Makita grinders, etc.) When cruising at lower rpm, the fans would be effectively under-volted as the alternator is not putting out the full 120V.

If this ends up not working, anyone know of any reasonably priced DC motor solutions?

I'm thinking of driving a fan like this:



http://www.flex-a-lite.com/catalogs/merchant.mv?Screen=CTGY&Store_Code=heavyduty&Category_Code=4600series
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luvrbus
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« Reply #6 on: June 01, 2010, 08:08:00 PM »

Roy the one on the add looks gray and blue with a mask on the front with a nice front bumper on the front they were asking 12,000 for it.
 I can not get the link to work for you maybe some of the smart guys can bring it up lol.


good luck
« Last Edit: June 01, 2010, 08:13:51 PM by luvrbus » Logged

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RoyJ
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« Reply #7 on: June 01, 2010, 08:20:49 PM »

Roy the one on the add looks gray and blue with a mask on the front with a nice front bumper on the front they were asking 12,000 for it.
 I can not get the link to work for you maybe some of the smart guys can bring it up lol.


good luck


That's definitely not the one, but I think I might have seen that one as well. IIRC, it does look somewhat similar to mine.

My bus is natural color (stainless with aluminum window panels), and the trims are painted red. I'll take some pictures once I've got it all polished up.

Some old service receipts list the model as H340, but I've googled around and found no such thing. Some Canadian only coach perhaps?
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« Reply #8 on: June 01, 2010, 10:18:30 PM »

Roy - a '64 H340 would be a 'rare' bird indeed - thanks for paying attention in school -

"What I'm guessing is that electric fans can blow a lot of CFM, but without the hp to back it up, they can't do so WHILE maintaining useful static pressure. Couple that to the thick radiator used on coaches, and you can smell (literally!) disaster"

Couldn't have said it better myself - Good Luck with your coach - Sounds like your first post-graduate experiment
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« Reply #9 on: June 01, 2010, 10:22:38 PM »

Welcome to our wild and crazy world !!

I am in the process of removing my A/C condenser which uses a hydraulic fan, which I will no longer need, if the deal gets done.

It cools a 36" X 36" X 6" condenser, so I imagine it might be helpful in your application.

If you are unable to get the situation resolved with the radiators and fans, let me know and we may be able to work out a deal for the fan.

I also have the two condensers that are just collecting dust !!

Keith
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« Reply #10 on: June 02, 2010, 04:42:35 AM »

Roy,

Lots of buses have large DC motors that ran both the evaporator & condenser fans. The venerable DN50 alternator that was original equipment has a plenty of power to drive the motors. Some bus nuts here have removed the original equipment setup & installed other options. You should be able to pick up the discarded components & fabricate what you need.

As a side note, you may want to look at the specs before you use an AC condenser for a radiator. Those are two different applications. The condenser was designed to convert a gas to a liquid by removing heat. The other just removes heat from water.

YMMV,

TOM
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« Reply #11 on: June 02, 2010, 05:04:04 AM »

As far as model call prevost car with serial number or I just saw site that has prevost listed by serial number and tells to whom they were sold and spec. Hydraulic fans can be easily driven by a belt operated auto power steering pump.one large fan blade easier to put shroud around and control air flow.unlimited blade configur around...Just a thought. need pictures.....possible a prestiage (sp)model...need pictured of rad area...being a engineer you can apreciate the KISS principle it does well in our hobby especially  when trying to get part on the road...Welcome and fyi there is no age requirements..we are all crazy Bus Nuts
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« Reply #12 on: June 02, 2010, 05:11:44 AM »

My instinct would be to use an engine driven fan, either belt or hydraulic, since the power levels can be pretty high.  I'm not sure if letting an alternator run at high voltage is a long-term reliable thing to do, if you are going to pull 16hp out of it you have to put more than that into it, and they just aren't designed for that loading.  I also don't know how to figure the hp load to accomplish the air flow, but at a guess and looking at some charts put out by Caterpillar on their engines, you might need 20 hp.  I use a rule of thumb of 1,000 watts for 1 HP output of electric motor, so 20,000 watts?  That's a lot of electricity, but it's not a lot of mechanical power.

I also have this idea that an alternator may be power limited, in other words it can be designed for 100 amps at 12 volts for 1,200 watts, or 50 amps at 24 volts, or 10 amps at 120 volts.  Certainly the literature on alternators that come in various voltages implies that sort of relationship.

Brian
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« Reply #13 on: June 02, 2010, 10:03:34 AM »

I was NOT suggesting using an A/C condenser as a radiator, but the hydraulic fan might serve your purpose.

The condensers are available, but they are for A/C, not cooling an engine.

Sorry about being confusing.

Keith
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« Reply #14 on: June 02, 2010, 10:15:32 AM »

Could a unused ac condensor be used to supplement cooling??have wondered???or heater core?Huh
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