Author Topic: DIY Air resistive loads?  (Read 18928 times)

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DamonHD

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Re: DIY Air resistive loads?
« Reply #27 on: January 23, 2014, 12:00:09 AM »
I second that caution.

Rgds

Damon

joestue

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Re: DIY Air resistive loads?
« Reply #28 on: January 23, 2014, 05:03:59 AM »
Not the dump load pwm issue again.

i've repeatedly said for well over 2 years now the issue is supply side inductance, not dump load side inductance.
http://johansense.com/bulk/resistor_pwm.JPG
http://johansense.com/bulk/pwm_resistor_1.JPG
http://johansense.com/bulk/pwm_resistor_2.png

provided the load is inductive or resistive, it doesn't matter. you could use a 500 foot spool of 12 awg as a dump load on *any* pwm dump load, and provided you've got a diode across the coil,* it won't know the difference.
*The dump load should already have one, but it may not be heatsinked sufficiently for continuous currents created by a mostly inductive load, for example, a 500 foot spool of wire.

A capacitor across the dump load will cause the switch to fail due to peak current, that's it, nothing more or less.
An additional failure mode exists if an IGBT is used as a switch without a free wheeling diode across the dump load, or the igbt... in which case, whoever designed it needs to find a new job.

solving the audio problem is more a matter of finding sufficient inductance to generate continuous currents in the dump load resistor+capacitor.
and that inductance is expensive, compared to just increasing the frequency to 16+khz.

SparWeb

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Re: DIY Air resistive loads?
« Reply #29 on: January 24, 2014, 08:01:38 PM »
Joe,
Can you suggest a way that Vortechs should be going about finding that ideal inductance?  Or a range in Henries that he should be aiming for? 

I'm sure there is a more cost-effective solution than the 500 foot spool of wire, but I don't know how to design it.  Sounds like you do, and both the OP and I would like to learn more about it.  As I said, the noise from mine is quite loud and a "hush" kit would be welcome here, too.

Since the OP didn't participate in the thread you are referring to, and neither did I, perhaps it is helpful to refer us to that?
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

niall2

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Re: DIY Air resistive loads?
« Reply #30 on: January 24, 2014, 08:42:29 PM »
i wonder if "just leaving it alone" abet with the noise problem might be best in the long run Vortechs ?.....

if the natural pwm hz is in the audible range , its going to be hard to get rid of it without stressing the power fets in some way ? ....

it is an extremely annoying noise ...almost grates on your teeth  >:(...the silver lining is as long as you can hear it.......... its working

sorry thats not very scientific..... :)



 

 

joestue

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Re: DIY Air resistive loads?
« Reply #31 on: January 24, 2014, 10:21:04 PM »
my past posts are mostly incoherent rambling  :-X

plug your numbers in here
http://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml

I think we can assume that the noise level is proportional to current ripple, but it might not be.
you might not need much of an inductor to kill the noise, just enough to soften the rising edge of the current waveform.

air core inductor calculator is here
http://www.daycounter.com/Calculators/Air-Core-Inductor-Calculator.phtml

again, the issue is the cost of the inductor, that's about it.
capacitors are cheap.

if the switching frequency is below ~3Khz, the best option is to use an iron cored inductor.. it will get warm and make noise as well however.

Regarding experimenting with what works...
find the pwm frequency, and use that to find the minimum inductance you need to keep the current ripple below 50%.
make sure you have at least that much inductance, then add capacitors across the dump load. inductance first, then capacitors.
otherwise you'll end up with other problems..
« Last Edit: January 24, 2014, 10:33:15 PM by joestue »

niall2

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Re: DIY Air resistive loads?
« Reply #32 on: January 24, 2014, 11:18:56 PM »
the morningStar controller makes a lot of noise in dump mode.......i think its the nature of the beast....hard on/off fets   

they have 6 ( at least ) big transorbs on the cct board .....it doesent like transient spikes from inductance in the load .....seems to hate them with a vengeance....

 



   

joestue

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Re: DIY Air resistive loads?
« Reply #33 on: January 24, 2014, 11:23:14 PM »
the morningStar controller makes a lot of noise in dump mode.......i think its the nature of the beast....hard on/off fets   

they have 6 ( at least ) big transorbs on the cct board .....it doesent like transient spikes from inductance in the load .....seems to hate them with a vengeance....
 

 
ahahaha.. ok there's the key right there..
the transorbs on the board are there to absorb the energy dumped into the mosfet, because they are cheaper than capacitors.

i can see its going to be a pain to figure out.. is the noise from the Di/Dt on the input, or the output of the pwm converter?


also, is there a diode, or does it have transorbs across the dump load (but no diode)?
 

niall2

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Re: DIY Air resistive loads?
« Reply #34 on: January 24, 2014, 11:50:56 PM »
" the transorbs on the board are there to absorb the energy dumped into the mosfet"

i,ve no idea joestue  :)......but i doubt it ....the transorbs would be a last resort ?...

arent transorbs just a fancy zener diode anyway ?

niall2

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Re: DIY Air resistive loads?
« Reply #35 on: January 25, 2014, 12:27:45 AM »
sorry ...thinking about it a bit more , yes the transorbs would soak up the damaging spikes....

i seen one controller burnt out , covered in soot and talked to a tech in morningstar ....he said clean up the board  , take out the fused transorb and re boot the controller

it worked fine ...5 transorbs left  :)
 

Vortechs

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Re: DIY Air resistive loads?
« Reply #36 on: January 25, 2014, 05:14:03 AM »
Thanks Joestue, you seem to know what you're talking about, unfortunately I dont,,, it's all a bit too technical for me. I'm the original poster of this thread. I have a Trace C40 controller using a Ohmrite
PFE5K1R00E 1ohm power resistor. I'm dumping about 500w into it at 28V. The noise was about the level of the average person talking, so I removed the ceramic core from the resistor and that made it quieter but now it's like having bad tinnitus all the time, a very high frequency noise, I've put a small fan blowing air over the resistor core to try and hide the high pitch noise but it doesn't help much.
I'm almost at the point of giving up on air resistive loads, I dont want to heat water so I'm now thinking about converting an oil filled radiator to a 24v immersion heater, any reason you can see that that wont work or be quiet for me? 

OperaHouse

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Re: DIY Air resistive loads?
« Reply #37 on: January 25, 2014, 07:22:15 AM »
To put it simply, an inductor resists any change in current.  Whether it is at 0A or 10A, it wants to stay at that current.
When the dump FET turns on the inductor resists the increase in current till the magnetic core saturates.  If the inductor
is at 10A when the dump FET turns off, The inductor will generate whatever voltage is necessary to continue that 10A current
flow till the magnetic field collapses.  The theoretical voltage is infinite, the practical voltage is large enough.  For that
reason suppression devices are included.  A mov, zener, etc is included to protect the FET.  The clamp voltage must be above any
normal operating voltage the dump controller will ever see. 

The problem is that these devices, even a half dozen of them in parallel, are designed for occasional transients and not continuous
duty into an inductive load.  Remember the power dissipated is a function of the volts across the device.  This is why a "free
wheeling diode" should be used since the voltage across it will e less than a volt.  And the diode needs to be fast, not a general
power supply diode.  Diodes take time to turn on and turn off.  Durring that time the voltage accross the diode will be higher and it
will generate more heat.  If this is just once and a while it isn't an issue.  If it is continuous, the power dissipated in the diode
can be several times what you expected.

joestue

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Re: DIY Air resistive loads?
« Reply #38 on: January 26, 2014, 03:26:30 AM »
@ Vortechs
I would certainly install it inside an oil radiator or something.

There are a few options to reduce the noise.
1) install capacitors across the battery supply cables, as close to the dump load as you can.
1a) do not be surprised if they explode
1b) if they get warm, install more of them.

2) After installing capacitors, increase or decrease the frequency. you might be exciting some mechanical resonance.
2a) I am not sure if this is possible with a C40? someone who has one can verify?

3) Verify if there is a catch diode inside the dump load. verify that it can handle the same current as the dump load. if there is no heatsink, install another diode. the 30 amp diodes found in computer power supplies will work great. it appears there is room inside the C40 (there should be one already)
3a) install as much inductance in series with the dump load as you can get. for the current you're dealing with three microwave oven primaries on the same core configured in parallel will be sufficient (for 120 volt systems, do you live in 220 volt country?) set the core gap to 1-3mm.

4) After adding much inductance to the dump load, install a few single digit uF capacitors across the dump load. non electrolytic only, look for the plastic film capacitors. they need to be rated for at least twice the battery voltage.

niall2

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Re: DIY Air resistive loads?
« Reply #39 on: January 26, 2014, 08:26:51 AM »
Vortechs  ...heres a 48v 900w element in a oil storage heater.....i dont hear any "buzz" from it , but lots from the controller beside it ...

one problem is these elements are fairly short (about 10 inchs ) so your really only utilizing half the radiator....theres usually a bung in the top of the heater thats the same thread as the element bung at the bottom , so the 48v volt element was put in on the top and the heater turned upside down ....

getting a thread adapter is the tricky bit (depending on the thread size of the heater) 

7893-0 

niall2

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Re: DIY Air resistive loads?
« Reply #40 on: January 26, 2014, 07:24:05 PM »
"also, is there a diode, or does it have transorbs across the dump load (but no diode)?"

i,m not really sure Joestue.....the fused transorb was one of a set of 3 in parallel directly over  +/ground.....kind of like fuses

there may be others over the source/drains of the mosfets ? ...maybe

"solar converter" in Canada make a pwm direct heating controller that seems to make no noise at all...





 

Vortechs

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Re: DIY Air resistive loads?
« Reply #41 on: January 27, 2014, 01:22:17 PM »
There's no diode across the power resistor dump load, this is the type I have:

http://www.ebay.com/itm/OHMITE-PFE5K1R00E-Wirewound-Resistors-Chassis-Mount-1-Ohm-1089-WATTS-2-PCS-/300888671916?pt=LH_DefaultDomain_0&hash=item460e5cc6ac

As far as I'm aware you cant adjust the frequency on the C40 controller, but I'm no expert.

I've bought a 24V 600W water heating element and acquired an old Delonghi 2KW oil filled radiator, it has a 1.5" threaded element hole in the bottom and the same size bung hole in the top. The new element is the same length as the old 220v one but has 1.25" thread, so I'm going to need a bushing reducer to make it fit. The heater has no thermostat so must be capable of dissipating 2KW continuously so the 500W should hopefully be no problem for it.
I'm glad to see someone else has successfully converted one of these before, I'll let you know how it goes...

joestue

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Re: DIY Air resistive loads?
« Reply #42 on: January 27, 2014, 03:44:42 PM »
well there should be a diode internally to the C40 but I can't find where they would put it.
sure looks like some kind of funky device attached to the heatsink, maybe they heatsinked the MOVs?

in any case externally the diode would be connected across the dump load.
as i mentioned the 30 amp 45 volt diode common to most ATX computer powersupplies will be more than sufficient, just don't connect it backwards and short out the dump load.

Vortechs

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Re: DIY Air resistive loads?
« Reply #43 on: January 30, 2014, 12:48:52 PM »
The 24V 600W water heating element arrived today so I put it in the old Delonghi oil filled radiator I found, connected it up to the controller, and ,,,,,,,  silence,  :)

I took temperature readings of the radiator every half hour for the first few hours, highest it went was 68*C / 154*F mostly sat between 50-60*C / 122-140*F

Vortechs

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Re: DIY Air resistive loads?
« Reply #44 on: January 31, 2014, 01:03:04 PM »
After a whole night of full load the rad temp was 187*F / 86*C :)


niall2

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Re: DIY Air resistive loads?
« Reply #45 on: January 31, 2014, 01:42:28 PM »
:)...

that was quick ....the long element seems much better than mine

twins then ....

SparWeb

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Re: DIY Air resistive loads?
« Reply #46 on: February 01, 2014, 09:25:05 PM »
That's excellent.
What a simple and elegant solution to the problem.
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

XeonPony

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Re: DIY Air resistive loads?
« Reply #47 on: February 02, 2014, 08:28:26 AM »
and very functional too man that must be great for winter heating!
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

Vortechs

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Re: DIY Air resistive loads?
« Reply #48 on: February 02, 2014, 12:27:08 PM »
It's brilliant for making use of the overnight power, you wake up to a warm house  ;D Surprised more people aren't using them.

XeonPony

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Re: DIY Air resistive loads?
« Reply #49 on: February 03, 2014, 05:17:53 AM »
I used a 500w base bord heater bolted under the beds head board, I ran a 230v AC turbine and the heater and some lights where my balast load, now I am sadly grid connected again as I moved tot he praries and no hills here for water, so need to build a wind genny and a bigger array.
Ignorance is not bliss, You may not know there is a semie behind you but you'll still be a hood ornimant!

Nothing fails like prayer, Two hands clasped in work will achieve more in a minute then a billion will in a melenia in prayer. In other words go out and do some real good by helping!

Vortechs

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Re: DIY Air resistive loads?
« Reply #50 on: January 07, 2017, 12:21:03 PM »
After a whole night of full load the rad temp was 187*F / 86*C :)



Three years on the oil filled radiator with a 600W element as dump load is still working perfectly. I did have one issue with it so I just wanted to add this update for anyone else thinking of doing the same.

After the first few months one of the cables started over heating and melted, so I bought some very heavy duty 6mm speaker cable and made up a heat-sink / low resistance connector, which solved the problem and has been perfect ever since.



It's made out of 10mm copper pipe. The cable was striped and inserted into the pipe before it was flattened and drilled. :)


SparWeb

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Re: DIY Air resistive loads?
« Reply #51 on: January 07, 2017, 05:27:36 PM »
Happy new year!
Comfort and warmth, indeed :)
No one believes the theory except the one who developed it.  Everyone believes the experiment except the one who ran it.

System spec: 135w BP multicrystalline panels, regulated by Xantrex C40, DIY 8ft diameter wind turbine, regulated by Tri-Star TS60, 800AH x 24V AGM Battery, Xantrex SW4024

Bruce S

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Re: DIY Air resistive loads?
« Reply #52 on: January 09, 2017, 07:10:21 AM »
It's great to see updates from the older posts too.
Congrats on the uses and thanks for the update!!
A kind word often goes unsaid BUT never goes unheard

plasmahunt3r

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Re: DIY Air resistive loads?
« Reply #53 on: January 17, 2017, 09:35:47 PM »
I know this is not exactly what the topic requested, but why not use MOSFET's as the Dump Load Resistors.  They are cheaper.  You can get a couple of 300W MOSFETs for around $5.  They would need to be mounted on heat sinks.  The bigger the heat sink, the better. 

This seems to be better and simpler than these Frankenstein setups.

I drew up a circuit to show what I mean.