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converting 12V to 24V
Posted by
Simon
on 19 Aug, 2014 18:52
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I was asked today if I can convert 12V to 24V. We need to supply a fan that runs on 24V but the customers vehicle runs on 12V. So I'm thinking, for 24V@40A (worst case and over) is it feasible to run a H bridge and then voltage double rectify it to get 24V, being a Fan the exact voltage and regulation are of no concern. Or is a SMPS so much better ?
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Problem with a boost converter is the switch current is much higher than the output current so it might be a bit of work to get a Switching regulator to bump up 12 to 24 at 40A.
What kind of KW fan runs off DC?!
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#2 Reply
Posted by
SeanB
on 19 Aug, 2014 18:59
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Boost converter will be better. If the fan is thermally controlled then you can use the SMPS control to do things like speed control ( low, med and high speed are easy with no switching letting 12V through, 18V and 24V to the fan) and on off switching as well.
40A with a voltage doubler using capacitors means either massive capacitors or running switches in the MHz range with all the EMI and heat. Choke with big power MOSFET and diode ( here active rectification will be a definite power saving and make for a smaller heatsink) at 20kHz to 100kHz or so will be a lot smaller and cheaper.
Of course a 12V fan is going to be a lot cheaper as well, and likely will be just as good and only cost 30 pounds or so, about the cost of the converter in any case.
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#3 Reply
Posted by
Simon
on 19 Aug, 2014 19:00
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It's automotive, Alibaba have plenty of 12/24V units running 960W, Bosch make a very nice fan that runs 12V 48A, it's the dogs goolies in the business.
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#4 Reply
Posted by
Simon
on 19 Aug, 2014 19:02
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Boost converter will be better. If the fan is thermally controlled then you can use the SMPS control to do things like speed control ( low, med and high speed are easy with no switching letting 12V through, 18V and 24V to the fan) and on off switching as well.
40A with a voltage doubler using capacitors means either massive capacitors or running switches in the MHz range with all the EMI and heat. Choke with big power MOSFET and diode ( here active rectification will be a definite power saving and make for a smaller heatsink) at 20kHz to 100kHz or so will be a lot smaller and cheaper.
Of course a 12V fan is going to be a lot cheaper as well, and likely will be just as good and only cost 30 pounds or so, about the cost of the converter in any case.
The fan is brushless so I need to leave controls up to the fan. Apparently EMI is nor a problem. Yes switched mosfets for rectification will certainly be more efficient as in SMPS.
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#5 Reply
Posted by
SeanB
on 19 Aug, 2014 19:04
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Look at your local automotive airconditioning suppliers, you can get a fan that will both fit, give the air flow and will run off 12V as well.
Retrofitting a truck aircon unit to operate on a smaller vehicle Simon? Get 12V auxiliary aircon fans and use them instead with the standard block parts. Otherwise have a 24V battery and alternator in the engine compartment to run it all.
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For high-current loads like that, the traditional solution is to simply provide an additional 12V battery in series.
Of course, you must make provision to charge the battery separately from the primary circuit.
What on earth kind of fan takes 480 watts? That seems unreasonable to expect to power from the normal vehicle battery.
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#7 Reply
Posted by
Simon
on 19 Aug, 2014 19:08
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I don't know what sort of vehicle it is but it's a new built as far as i know and the fans do need to be powerful sometimes, that 12V 48A fan has been used for years and was developed by bosch for audi initially, yes it can take of from the bench, I've never run one full power.
Having a second battery means that either we need to charge it or a second alternator, both options are as complicated unless the duty on the fan is low so a low power converter keeping a series battery topped up can handle it. i will ask my colleague tomorrow.
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#8 Reply
Posted by
Sigmoid
on 19 Aug, 2014 19:18
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Whoa, that's one big fan... xD
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#9 Reply
Posted by
Simon
on 19 Aug, 2014 19:23
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Engine cooling does not happen on it's own. I think many Audi's have a mechanical fan running permanently off the engine plus the powerful auxiliary fan. once you exhaust electric fans you turn to fans running on hydraulic motors that makes for a more efficient system and these days speed control and complicated electronic controls are being introduced to hydraulic systems because it still pays to keep it hydraulic but it needs regulating. I don't know why they want so much power in this case and are using an electric fan.
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Sure, probably most modern vehicles use electric fans for supplemental air-flow over the radiator.
But they use fans designed for the primary vehicle battery voltage.
Why are they deploying a 24V fan in a 12V vehicle?
There appears to be a fundamental design flaw here.
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#11 Reply
Posted by
Simon
on 19 Aug, 2014 19:31
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Once you above a certain power most fan manufacturers like to shift to 24V and assume that for the sort of power demands the vehicle will be running 24V I have no idea of the electrical background of the vehicle. apparently a 12v version is available but very hard to obtain.
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#12 Reply
Posted by
mzzj
on 19 Aug, 2014 19:54
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Simon and his projects again
I would choose smps with full bridge, 20 to 100khz operating freq and schottky diodes for rectification. Something like etd59 or EE 55 size ferrite core will handle the required power easily.
Nothing that difficult for someone with enough experience with high current power supplies... Until Simon tells us that it has to potted, low outgassing for hard vacuum, has to withstand 5000g acceleration for 10 minutes and has to operate at liquid helium temperatures
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#13 Reply
Posted by
Simon
on 19 Aug, 2014 21:17
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#14 Reply
Posted by
mzzj
on 19 Aug, 2014 21:34
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#15 Reply
Posted by
mzzj
on 19 Aug, 2014 21:37
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#16 Reply
Posted by
Simon
on 20 Aug, 2014 05:46
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Well obviously they will want it cheap......... The joys of working for a mechanical company that just see electronics as magic
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#17 Reply
Posted by
Rasz
on 20 Aug, 2014 08:40
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It's automotive, Alibaba have plenty of 12/24V units running 960W, Bosch make a very nice fan that runs 12V 48A, it's the dogs goolies in the business.
-put two batteries in the car
-put 48v alternator in the car
-put proper 12V fan
-learn to just say 'no'
-tell management 'sure, it will cost $1K'
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#18 Reply
Posted by
Simon
on 20 Aug, 2014 08:48
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It's automotive, Alibaba have plenty of 12/24V units running 960W, Bosch make a very nice fan that runs 12V 48A, it's the dogs goolies in the business.
-put two batteries in the car
-put 48v alternator in the car
-put proper 12V fan
-learn to just say 'no'
-tell management 'sure, it will cost $1K'
- It's not my car and who said it's a car ?
- Why 48V ?
- As already mentioned at this power level 12V is rare for a good reason
- What not get to spend time learning something new while being very essential as i can develop new products?
- You can buy one off the shelf for less
Have you ever actually worked in engineering ?
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#19 Reply
Posted by
firewalker
on 20 Aug, 2014 09:19
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The battery should also be capable of providing ~100 amps plus any other consumption. What will be the duty cycle of the fun? Continuous operation?
Alexander.
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#20 Reply
Posted by
bktemp
on 20 Aug, 2014 09:22
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It sounds like there is no need for a perfectly regulated output voltage. This makes everything a lot easier:
All you need is a centre tapped transformer with 1:2 windings (or a bit more to compensate losses) and many paralleled mosfets that drives the thing. Have a look at big car audio amplifiers. Most of them use a similiar approach. There is basically no regulation of the output voltage, the output voltage follows the input voltage. The only purpose of the SMPS controller is to limit the no load voltage. Otherwise it runs at 100% duty cycle.
Most of those power supplies do not have any kind of overcurrent protection. If something goes wrong, all mosfets explode.
If you need to add some protection it can get quite complicated, 100A is a lot of current, especially at high frequencies.
It might be easier to use 2 or 4 (phase shifted) converters in parallel.
Using active rectification with this design can be as simple as adding auxiliary windings to the transformer for driving the gates.
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#21 Reply
Posted by
Simon
on 20 Aug, 2014 10:16
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Yes i have had a transformer suggestion, I would need to obtain one and transformers are not my area. No regulation is required so yes it just needs to double the input.
I have tried to find out the duty of the fan but as usual we are non the wiser. I think they have now found a fan that does the power at 12V so maybe I won't need to try and make this or find something after all.
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#22 Reply
Posted by
diyaudio
on 20 Aug, 2014 10:39
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It sounds like there is no need for a perfectly regulated output voltage. This makes everything a lot easier:
You cannot make a switching converter (boost or push-pull) regulate in a CAR as the output power is proportional to the battery current that's always less that what is was when you attached the converter. (car audio manufactures no this very well so they use a fixed duty cycle and have active shut down using under voltage lockout when condition's doesn't satisfy)
To the author
You can use a simple TL494 some PID scheme of your choice with good magnetics from
http://www.arnoldmagnetics.com/ that all you will struggle with.
Those alibaba china converters should never be trusted in automotive environments such as a car, where environmental conditions are harsh and unpredictable, and peoples lives are at risk.
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#23 Reply
Posted by
Simon
on 20 Aug, 2014 10:45
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This is not for a car, apparently they have the required power available.
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#24 Reply
Posted by
Rasz
on 20 Aug, 2014 14:21
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- It's not my car and who said it's a car ?
you did:
>customers vehicle runs on 12V
unless you meant a bike, or an ATST walker
- Why 48V ?
24
- As already mentioned at this power level 12V is rare for a good reason
and yet someone found one already
good reason was probably 'gonna pick this one and make someone else worry about it'
- What not get to spend time learning something new while being very essential as i can develop new products?
why not use proper components instead of bodging?
>>-tell management 'sure, it will cost $1K'
- You can buy one off the shelf for less
whole point of that line is to bounce your problem back up to the source, not to buy $1K box. Source of your problem was someone else arbitrarily deciding on a wrong component, and making your job unnecessarily difficult.
Have you ever actually worked in engineering ?
Are you saying engineers job is to bodge shit to implement something unqualified people came up with?
Even in case 12V fan couldnt be found, the easiest solution would be custom fan, or a bare fan + 12V motor.
. I think it's all conjecture at the moment as the suggestion was an act of desperation in not being able to get a fan powerful enough at 12V but i'm certainly not going to let that get in the way of a good project