Puppeteer

Author Topic: WVO preheater  (Read 20996 times)

dieselgman

  • Hero Member
  • *****
  • Posts: 3139
    • View Profile
    • Lister Parts
Re: WVO preheater
« Reply #15 on: February 13, 2014, 03:26:37 PM »
I have some 480volt 10kW heaters around the shop that I was wondering about using with 240volt. No diodes required? Any other losses involved?

dieselgman
Ford Powerstroke, Caterpillar 3304, Cummins M11, Too many Listers to count...

BruceM

  • Hero Member
  • *****
  • Posts: 2312
    • View Profile
Re: WVO preheater
« Reply #16 on: February 13, 2014, 07:18:57 PM »
 You'll need to check their schematic to make sure they aren't using 480V relays or time delayed relays requiring 480V.  If so, they'll have to be modified. 

 Send me the schematic or post it and I'll take a look.


Thob

  • Sr. Member
  • ****
  • Posts: 255
    • View Profile
Re: WVO preheater
« Reply #17 on: February 13, 2014, 10:17:23 PM »
When you cut the voltage in half, then the amperage will also be one half (assuming a linear device).  Thus the 1/4 wattage.

What a single diode will do in AC feeding a heating element is only allow 1/2 of the AC cycle to pass thru, effectively giving 1/2 the voltage.  But that only works once (you can't stack multiple diodes to keep cutting it in 1/2), it only works for AC (not DC), and it assumes that the generator doesn't mind you're only using 1/2 of the AC cycle, etc.  It also assumes you didn't use a full wave bridge, but just a single diode.
Witte 98RC Gas burner - Kubota D600 w/ST7.5KW head.
I'm not afraid to take anything apart.
I am sometimes afraid I'm not going to get it back together.

buickanddeere

  • Hero Member
  • *****
  • Posts: 792
    • View Profile
Re: WVO preheater
« Reply #18 on: February 13, 2014, 11:44:43 PM »
I have some 480volt 10kW heaters around the shop that I was wondering about using with 240volt. No diodes required? Any other losses involved?

dieselgman

2.5Kw on 240volt AC

dieselgman

  • Hero Member
  • *****
  • Posts: 3139
    • View Profile
    • Lister Parts
Re: WVO preheater
« Reply #19 on: February 14, 2014, 12:54:48 AM »
Thanks guys, I will experiment a bit to see what the current actually reads on the lower voltage. I have to get some single-phase blower motors to make this work.

dieselgman
Ford Powerstroke, Caterpillar 3304, Cummins M11, Too many Listers to count...

buickanddeere

  • Hero Member
  • *****
  • Posts: 792
    • View Profile
Re: WVO preheater
« Reply #20 on: February 14, 2014, 01:06:57 AM »
Thanks guys, I will experiment a bit to see what the current actually reads on the lower voltage. I have to get some single-phase blower motors to make this work.

dieselgman

Oh yea of little faith....................

ronmar

  • Hero Member
  • *****
  • Posts: 1225
    • View Profile
Re: WVO preheater
« Reply #21 on: February 14, 2014, 11:44:08 PM »
Diode only allows current flow in one direction, so a 120V AC sine wave will have half of it's wave cutoff resulting in a 60V waveform.  That part of the waveform that is cutoff also occupies time, so the 120V sinewave becomes a 60V pulsed waveform with a 50% duty cycle.  SO half the voltage with only half the on time/energy density leaves you with 25% energy being delivered.  SO the  2KW heater becomes 500W give or take:) 
PS 6/1 - ST-5.

BruceM

  • Hero Member
  • *****
  • Posts: 2312
    • View Profile
Re: WVO preheater
« Reply #22 on: February 15, 2014, 03:50:47 AM »
I mentioned the relays as it is common that there is some sort of sequencing of elements; the full load surge current into a cold resistive load like that would be impressive. 

+1 for Thob's wattage approximation on 240V, +1 for Ronmar's diode wattage approximation.  Both will vary slightly for resistive heating elements operating at cooler temperatures, you may get slightly more than 1/4 the rated wattage.

veggie

  • Keep Calm and Start the Lister !
  • Sr. Member
  • ****
  • Posts: 353
    • View Profile
Re: WVO preheater
« Reply #23 on: February 15, 2014, 02:55:27 PM »
Thanks fellas for explaining the diode/AC element operation.
What type of diode is required to do this?
Obviously not your everyday circuit board diode.
I a guessing it may be purchased from an electrical supply shop rather than an electronics component place?

Cheers
veggie
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

BruceM

  • Hero Member
  • *****
  • Posts: 2312
    • View Profile
Re: WVO preheater
« Reply #24 on: February 15, 2014, 04:58:47 PM »
Right, Vege, at 0.75V drop time times the current through the diode being dissipated as heat, these are going to be big through bolt type diodes, (several in parallel) mounted on a big aluminum heat sink when you get to higher currents.  At high currents, the diode noise (EMI) will also be impressive without RC snubber suppression.  Forget AM radio reception near the heater. 

Diodes are sometimes used in portable, 1500 watt or less resistance heaters.  You're not likely to see them being used in high wattage devices because the cost and heat sinking required.  Most higher wattage devices, like electric boilers, will have multiple elements and sequencing on start up and/or selection of elements for variable ouput levels.


buickanddeere

  • Hero Member
  • *****
  • Posts: 792
    • View Profile
Re: WVO preheater
« Reply #25 on: February 15, 2014, 06:53:59 PM »
Diode only allows current flow in one direction, so a 120V AC sine wave will have half of it's wave cutoff resulting in a 60V waveform.  That part of the waveform that is cutoff also occupies time, so the 120V sinewave becomes a 60V pulsed waveform with a 50% duty cycle.  SO half the voltage with only half the on time/energy density leaves you with 25% energy being delivered.  SO the  2KW heater becomes 500W give or take:) 

 It's 120VAC half wave, not 60V half wave.
 P=I squared x R

ronmar

  • Hero Member
  • *****
  • Posts: 1225
    • View Profile
Re: WVO preheater
« Reply #26 on: February 15, 2014, 08:03:58 PM »
 You take a 120VAC(pk-pk voltage) sine wave, half of the sine wave goes positive and half of the sine wave goes negative.  If you run it thru a diode, you block say the negative going half of the signal.  This leaves you with a positive going 60V half wave with spaces between where the negative going half cycles used to be(50% duty cycle).

Now if you are starting with a 240VAC signal, then you would be left with 120V half cycles with spaces between where the missing cycles should be(50% duty cycle).  Still about 25% of the power delivered by the full 240VAC waveform.

But I thought we were discussing a 1400W 120V heating element...   
PS 6/1 - ST-5.

buickanddeere

  • Hero Member
  • *****
  • Posts: 792
    • View Profile
Re: WVO preheater
« Reply #27 on: February 17, 2014, 04:36:44 PM »
You take a 120VAC(pk-pk voltage) sine wave, half of the sine wave goes positive and half of the sine wave goes negative.  If you run it thru a diode, you block say the negative going half of the signal.  This leaves you with a positive going 60V half wave with spaces between where the negative going half cycles used to be(50% duty cycle).

Now if you are starting with a 240VAC signal, then you would be left with 120V half cycles with spaces between where the missing cycles should be(50% duty cycle).  Still about 25% of the power delivered by the full 240VAC waveform.

But I thought we were discussing a 1400W 120V heating element...   

   Don't know where you went to school for electrical theory?
   With a diode the applied power is now with one half of the entire sine wave. Measuring either and only the positive or negative portion of the complete sine wave.
   With 120V rms AC power through a diode. Between 0 and 180 degrees there will be for example a positive half of the sine wave. With a 170 volt peak. Then virtually nothing from 180 to 360 degrees.