Original bus heat blower speed

[Tim Strommen]

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.

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 ).

This 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 (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

[Brian Diehl]

Wow Tim!  Thanks for sharing. I'm looking forward to reviewing your design!

-Brian