Hello everyone,
I have a 1975 MC-5B shell heat ducts have been removed, I was wondering is there a switch that can be installed to lower the
blower speed? It's either on full (will run you out) or you have to turn it off. Can't keep it a constent temp!
Thanks for any impute!
Steve 5B........
Origninally, there was a temp sender in the bus that would open and close an electric valve that would allow freshly hot coolant into the heater core and that is what would controll the heat. Fans were on or off. I have not heard of a way to slow that monster motor. It uses an awful lot of juice. I bought a large truck heater box, core and 2 speed fan to replace the original system. I'd love to hear of a way to do this electrically.
Hi Steve,
No, they only have one speed. But, you can fabricate a sort of reastat or simular to ramp it down.
i'm sure one of our members will come up with an idea on how to build one..
Good Luck
Nick-
Hey Nick,
I was thinking a rheostat also, when the heat runs were in place for the windows it worked fine, when removed .....downhill from there..............Thanks!
Steve 5B............
BIG Rheostat! Have you seen how big the ones are for the defroster? You may need a second bus for one for that motor! :D
Here's a thought..
What if we could just have a battery switch to drop the voltage down to 12v to lower the speed.
I'm not sure if that would overheat the motor or not but, that would give us two speeds...??...??
Any thoughts?
Nick-
http://www.busconversions.com/bbs/index.php?topic=6954.0
Look for diode series voltage reducer.
Or if you want 2-speed switch:
1) 1pc SPDT center-off switch at 20a rated
2) 8pcs Diode at 3a x 200v or higher voltage, the better protection from damaging spike voltage.
Solder or terminal strip all diodes in series to make a 6 volts drop (each are .7volt drop) from one of two outer switch post to motor. Connect 25 amp fused power wire to center post. The remaining post wired to motor which is high range.
How to identify the diode polarity:
http://www.allaboutcircuits.com/vol_3/chpt_3/1.html
Nothing fancy or complex and low cost and work every time.
Very good price for less then 50 cent each:
http://www.mouser.com/Search/Refine.aspx?Ntt=511-BYW98-200%09
Radioshack cost 1.59 each:
http://www.radioshack.com/search/index.jsp?kwCatId=&kw=diode&origkw=diode&sr=1
FWIW
Sojourn for Christ, Jerry
Simplest way is just to restrict the air flow to something close to what it was originally by severely reducing the cross sectional of the outlet ducts between the blowers and the floor outlet.
Might be best to restrict it closer to the motor to reduce the air noise inside the bus, but the engine noise might mask it anyway. Try it by shoving a block of foam down to block say 3/4 of the area on each side.
Hi Tony,
Good Thought! The only problem when you restrict air flow on squirrl cages is they tend to speed up and may get even louder.
Jerry, Thanks! that will do it.. My blower is 24v, couldn't I try and drop it down to 12v?
Nick-
I think what you need is a pulse width modulation motor control. Maybe you could find one on ebay that would do the job. Jerry
I agree with Jerry,
I think this topic came up about a week ago at a different voltage, with the same set of answers... (use this link (http://www.busconversions.com/bbs/index.php?topic=6954.0)).
If you need a PWM circuit, and can't find a suitable one on the e-place - we can come up with one (in fact that seems like an idea for this board - where would we put scematics, PCB layout files, parts lists, and pictures etc. for free "open source" designs?).
Cheers!
-Tim
Quote from: Tim Strommen on January 23, 2008, 09:10:15 AM
I agree with Jerry,
I think this topic came up about a week ago at a different voltage, with the same set of answers... (use this link (http://www.busconversions.com/bbs/index.php?topic=6954.0)).
If you need a PWM circuit, and can't find a suitable one on the e-place - we can come up with one (in fact that seems like an idea for this board - where would we put scematics, PCB layout files, parts lists, and pictures etc. for free "open source" designs?).
Cheers!
-Tim
Tim, on the Help board would be a good place. A topic could be dedicated to just such animals.
Richard
Hey Richard, in that case - I'll design a PWM controller for free/open-source use and post it there (in a day or so).
I'll include the schematic, parts list (with prices and sources if I'm allowed), a board layout file (ExpressPCB - they are cheap and fast) and the source code for the PWM pulse generator Microprocessor.
The design will be for a low-side switched (that is, the ground leg of the motor is switched - not the "+" supply), 12-24VDC supply with a 20Amp-surge load. In the microprocessor code, I'll put in some basic spread spectrum stuff (using a pseudo-random-number-generator, with optional external "entropy" via a broadband white noise generator) for better EMI/RFI performance. For giggles, the design will support a 10K-linear potentiometer, I2C, and auto-baud-detecting multi-rate RS-485 control (the latter two for direct digital control and feedback).
Cheers!
-Tim
"The only problem when you restrict air flow on squirrl cages is they tend to speed up and may get even louder."
yes, but the original air system with the vent holes along the windows is also very restricted, so restricting the duct to approximate that condition is not going to introduce any more noise or fan speed than would have been there in the original setup.
May actually work well enough to satisfy the OP's requirements and is very cheap and doesn't require a soldering iron or a computer to do it.
Quote from: Tim Strommen on January 23, 2008, 02:26:34 PM
Hey Richard, in that case - I'll design a PWM controller for free/open-source use and post it there (in a day or so).
I'll include the schematic, parts list (with prices and sources if I'm allowed), a board layout file (ExpressPCB - they are cheap and fast) and the source code for the PWM pulse generator Microprocessor.
The design will be for a low-side switched (that is, the ground leg of the motor is switched - not the "+" supply), 12-24VDC supply with a 20Amp-surge load. In the microprocessor code, I'll put in some basic spread spectrum stuff (using a pseudo-random-number-generator, with optional external "entropy" via a broadband white noise generator) for better EMI/RFI performance. For giggles, the design will support a 10K-linear potentiometer, I2C, and auto-baud-detecting multi-rate RS-485 control (the latter two for direct digital control and feedback).
Cheers!
-Tim
Tim, I'm looking forward to this! I like to dabble a little bit in electronics and wish I understood it much more than I currently do. Thank you so much for doing this!
Quote from: Tim Strommen on January 23, 2008, 02:26:34 PM
Hey Richard, in that case - I'll design a PWM controller for free/open-source use and post it there (in a day or so).
I'll include the schematic, parts list (with prices and sources if I'm allowed), a board layout file (ExpressPCB - they are cheap and fast) and the source code for the PWM pulse generator Microprocessor.
The design will be for a low-side switched (that is, the ground leg of the motor is switched - not the "+" supply), 12-24VDC supply with a 20Amp-surge load. In the microprocessor code, I'll put in some basic spread spectrum stuff (using a pseudo-random-number-generator, with optional external "entropy" via a broadband white noise generator) for better EMI/RFI performance. For giggles, the design will support a 10K-linear potentiometer, I2C, and auto-baud-detecting multi-rate RS-485 control (the latter two for direct digital control and feedback).
Cheers!
-Tim
Tim, post it here on the main board first so that everybody sees it. I will later move it to the help board like I do a lot of the OT posts.
Richard
Does anyone know what the heater motor draws? I seem to remember that it it is over one horsepower.
Quote from: Stan on January 23, 2008, 05:11:15 PM
Does anyone know what the heater motor draws? I seem to remember that it it is over one horsepower.
Doesn't the Big Blower (OTR) have a 70 amp breaker on it? I can check mine, but I believe it's something like that. The PWM controller would be great for the driver's HVAC, though.
David
Is the original problem that the temperature in the coach is now uncontrolable?
Restore the temp control circuitry and the fact that the duct work is gone will not be an issue.
What happened to the temp sensor in the air intake?
Is the water valve and its wiring functional?
let's fix this mouse trap, not invent a new one...
happy coaching!
buswarrior
Quote from: DavidInWilmNC on January 23, 2008, 05:22:56 PM
Quote from: Stan on January 23, 2008, 05:11:15 PM...Does anyone know what the heater motor draws? I seem to remember that it it is over one horsepower...
...Doesn't the Big Blower (OTR) have a 70 amp breaker on it? I can check mine, but I believe it's something like that. The PWM controller would be great for the driver's HVAC, though...
Depends on what the system votage is for the give bus. Some are 12V some are 24V. The carrier OTR blowers in my Gillig are 24V and are breaker'd for 20Amps. Typically, the amps double for the same ammount of work at half the voltage.
Quote from: buswarrior on January 23, 2008, 09:20:27 PM...Is the original problem that the temperature in the coach is now uncontrolable?...
...What happened to the temp sensor in the air intake?...
...Is the water valve and its wiring functional?...
In my bus, I have a shut-off valve for isolating the OTR heating from the engine, but other than that, the booster pump controls the temperature via the thermostat. To give me more control, I replaced the dumb-switch thermostat with a digital temperature sensor and am now controlling the speed of the booster pump via PID controlled PWM to regulate the temperature (very stable). I planed on adding a secondary PWM to the blower to give me more than an On/Off control to the blowers (which was factory on my bus) so that I could hear my passenger (I only have one... ::)).
I'll increase the design current capablity, but this will probably increase the cost a lot (instead of $25-40, it may be $40-120, the cheapest n-type MOSFET I'm aware of is about $12 for ~15Amps@24V or ~30Amps@12V of switching - to control a 1HP load for each voltage {1HP = ~760Watts}, you'd need about three of those in parallel so you're looking at about $36 just in MOSFETS). I'll try to keep it as simple/cheap as possible.
As an asside, since we are talking about these kind of currents, the diode based approach may not br practical/safe give the high currents. Diodes which can sustain the high currents of a ~1HP motor are not cheap either, and the waste product of that approach is a lot of heat which needs to be moved somewhere (for example a 0.7 volt drop accross a diode which has a 60Amp load is 0.7 x 60 = 42Watts). Having a lot of these will almost build you a secondary heater just from the heat you need to remove from the diodes.
Cheers!
-Tim
P.S. Richard, I'll do as you say, post it here first. -T
Tim: You refer to OTR blowers, so I assime your bus has more than one. MCI and GM just have one motor and the 70 amp breaker mentioned on a MC-9 at 24 volts seems to ring a bell in my foggy mind.
Motor overloads are typically 125% of full load current so that would put the MCI motor at about 1 1/2 HP and your motors at about 1/3 HP.
Hi Stan,
Yeah, the Carrier unit I have has two motors, one for each of the plenums that ran from the back to the front of the bus (one on the left, one on the right). They are both about 1/3HP, and they are currently switched by a 100Amp solenoid "contactor" in the factory configuration.
Since yours is 70A @ 24V, that leads me to believe I should "go for broke" on the design and just design around a 2HP motor. That will add some expense for those who have that much of a load, but the "stuffing" of MOSFETs will be optional so one may purchase as many as their load needs I guess.
Cheers!
-Tim
The simplest way is to do like older auto heaters and control the amount of hot water flow with a valve without messing with the air flow. I plan to do this with my defroster water flow but on a bus the physics of this is sometimes more work than it is worth.
Modern autos use a hot/cold air blend to do the same thing.
Any fan is a fluid pump so if you obstruct the air flow either into or out of the pump/fan you increase the load on it and if you overload it the electric motor will overheat and fail. If the motor is in the incoming air flow you also decrease the cooling air to the fan motor.
My MC-8 manual mentions something about a 2-speed motor for the OTR HVAC. There's supposed to be a resistor or something located down by the blower motor for speed control, but it's not on mine. Perhaps it was just an option and was seldom installed. I'll have to check, but there's supposedlya small wire (routed along with the big cable) that I assume was the solenoid to switch the resistors. It's been a few months since I looked at it, but I seem to remember that being there. Couldn't we just use resistors for the speed control... like many cars do? I know they would get hot, but the blower would cool them. I haven't a clue as to what one would use for the resistor on something like this, but it seems to be what MCI had in mind; I know they weren't using any sort of electronic controller. Anyway, it's just a thought.
David
Quote from: gus on January 24, 2008, 01:20:40 PM...The simplest way is to do like older auto heaters and control the amount of hot water flow with a valve without messing with the air flow. I plan to do this with my defroster water flow but on a bus the physics of this is sometimes more work than it is worth...
This is what my systm does now via the speed control of the "booster pump" (which pull warm water from the engine cooling system and pushes it into the interior heat exchanger). The fan runs at full power all of the time when on currently, and it is possible to strike a ballance between circulated air and circulated water by controlling both the fan speed and the mixture tempurature of the heat coil.
Quote from: DavidInWilmNC on January 24, 2008, 01:24:03 PM
...There's supposed to be a resistor or something located down by the blower motor for speed control, but it's not on mine...
...Couldn't we just use resistors for the speed control... like many cars do?...
This is entirely possible, and is suggested by the "rheostat" control (a variable resistance device which splits the power available to the motor and the device based on its setting). Yes it will get hot, and running a motor designed for a specific voltage at a lower one is not really good for it (this is relative though since the implied load from the blower/fan-blades will go down with the speed). This discussion seems to be breaking into two paths - efficiency and ease. Efficiency goes to PWM, ease goes to the resistive voltage split option.
It's up to the individual to "do it their way..."
Cheers!
-Tim
Quote from: Tim Strommen on January 24, 2008, 03:35:21 PM
This discussion seems to be breaking into two paths - efficiency and ease. Efficiency goes to PWM, ease goes to the resistive voltage split option.
It's up to the individual to "do it their way..."
Cheers!
-Tim
My impression of the PWM controller was that it wouldn't handle the possible 70 amp load (likely to be actually 50-60 amps) from the big blower. It's very possible that my impression is incorrect... it'd be nice to have a way to efficiently control the speed. I'm going to see if I can rig this controller up to throttle back my driver's HVAC blowers.
David
Hi Guy's,
Here is a thought. Would a Rheostat off a welder work? My Millermatic 210 has one that goes up to 210 amps and I
think that is the DC side of the welder..
Nick-
Nick: A Miller Welder uses the same principle as your bus alternator. The rheostat controls the filed voltage in the generator.
That brings up another possibility for the heater motor control. Does anyone have the specs on the main heater motor. If they are shunt wound motors, they can be controlled by field voltage (low current) but if series wound they have to be armature control (high current)
"My MC-8 manual mentions something about a 2-speed motor for the OTR HVAC. "
I think it is an extra field winding - more field flux gives lower speed and this is automatically connected when in the heating mode. It doesn't have a large effect anyway.
Tim,
Will your heater circulation system work without the pump on?
Just curious, I can't tell what bus you have from the photo. My 4104 lists a circulation pump as optional eqpt but it circulates so well without one I'm not sure why one was ever needed.
Quote from: gus on January 25, 2008, 02:34:14 PMTim,
Will your heater circulation system work without the pump on?
Just curious, I can't tell what bus you have from the photo. My 4104 lists a circulation pump as optional eqpt but it circulates so well without one I'm not sure why one was ever needed.
Sorry for the late reply - no, there is no appreciable circulation in the heater coil when the pump is off. The fans (which are on or off) push so much air through the coil that any heated water that gets by the pump's impeller is "lost to oblivion" (I think the blower motors might be adding more heat at that point ;)).
Quote from: DavidInWilmNC on January 24, 2008, 03:57:52 PM
Quote from: Tim Strommen on January 24, 2008, 03:35:21 PMThis discussion seems to be breaking into two paths - efficiency and ease. Efficiency goes to PWM, ease goes to the resistive voltage split option.
My impression of the PWM controller was that it wouldn't handle the possible 70 amp load (likely to be actually 50-60 amps) from the big blower. It's very possible that my impression is incorrect... it'd be nice to have a way to efficiently control the speed. I'm going to see if I can rig this controller up to throttle back my driver's HVAC blowers.
David
This is an example of a "chopper" type motor controller for industrial vehicles (http://www.evparts.com/prod-CT1943.htm) (electric forklifts, golf carts, electric cars, etc.). It's rated for 650Amps - far more than a 1.5HP motor would ever draw... The above example link is to a retail site for which I do not do business with, nor do I or am I endorsing. I simply refer to that website as they have failry good technical data and pictures.
The design I'm drawing up is not as complicated (no Widows PC required for programming, nor will there be reversing and energy recover via regerenative braking), and thus should be much cheaper (this term is relative obviously - the current design is a little more than 10% the cost of the above linked controller so far). By doing some basic caluclations over the weekend, it looks like the limiting factor for a 2HP motor at 11.75VDC will be the size of the heatsink (the cheap heatsink I've picked out will limit the controller to ~80degC (176degF) ambient without forced cooling - so it will need to be mounted inside the cabin...). At 28.8VDC, the controller will have enough thermal head-room that it may be located in the engine compartment with the compartment temperature at 120degC (248degF).
Cheers!
-Tim
{LATE EDIT} P.S. the "mounted in engine compartment" and "mounted in the cabin" statements are assuming a DD 2-stroke with a high-temp shutdown of 240degF. This means that the design temp at thermal-overload of the engine should still allow the controller to be safely operated (i.e. it won't burst into flames). The recommendation will stand that the controller should be located in the closest proximity to the blower/fan motor - which means that mounting it within the return-air streem to the blower would be recommended (since the return air will be around 60-80degF from the cabin). -T
Wow Tim! Thanks for sharing. I'm looking forward to reviewing your design!
-Brian