# Water cooled toroids?



## evmetro (Apr 9, 2012)

I have an EMW 12000 that I use to charge a pack @127 volts, and the output toroid gets pretty toasty with it at that lower voltage higher current configuration. On a higher voltage pack, the input one builds up more heat, and on lower voltage packs the output one builds up more heat. I am going to have my output toroid rewound so that it does not get as hot, but I was wondering if there were water cooled ones available so that I could use the same specs as the one that is in there without overheating it. I googled them and saw a few possibilities, but I don't have the technical knowledge to know what the drawbacks would be or if anybody here with knowledge of how the EMW works had any thoughts on this idea?


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## evmetro (Apr 9, 2012)

That's what I was worried about. The DIY EV conversion market is probably not flooded with water cooled toroids.. Does anybody know enough electrical theory to know what would happen if I dipped the ones I have into something that would make them water proof and then submerged them into a water chamber that had circulation?


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## dedlast (Aug 17, 2013)

Tesseract or PSTechPaul would certainly be able to give you a better answer, but...

I would expect that water would change the inductance of the coils to some extent but I think it would be fairly minimal. Also, you aren't using them as chokes so that change wouldn't mean too much in the circuit anyway. 

As long as you can isolate the electricity from the water, I think it would work. 

Bill


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## Sunking (Aug 10, 2009)

Why don't you do use what utility transformers use to keep them cool and add thermal mass? Mineral Oil or Cooking Oil. 

Oil is an electrical insulator and does not conduct electricity like water. Few years back PC Gamers used PC Cases filled with either mineral oil or cooking oil. 

Every oil filled transformer today uses Mineral Oil. When you go by a sub-station and see those big transformers with cooling radiators has mineral oil being circulated.


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## Ai! (May 9, 2014)

only oil is capable of efficient cooling of this toroids, +1 to Sunking


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## evmetro (Apr 9, 2012)

Interesting. I recently changed a fuel pump in an ICE car and was fascinated that the pump was submerged in the gasoline, and both the positive and negative terminals were bare and exposed. I was taught at a young age to not take a bath with anything that is plugged into an outlet so I was puzzled to see the fuel pump submerged in the fuel, but after some research and a thread on this forum, I understand this kind of thing now.

I run an antifreeze mixture to cool my charger and controller, so I would have to add a second system for the toroid if I ran mineral oil. I suppose I could also just cool everything with the mineral oil so that I would not have to have two systems. I am excited about this, because I was concerned about what would happen if I had a coolant leak onto the windings. A leak like that would provide a path to the chassis...

Thank you guys for the replies. If I understand correctly, I will not need to waterproof the toroids, I can just bolt them into a sealed box with hose barbs tapped into it and I will need to make some contacts to pass the current through the box. This sounds pretty slick.


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## nimblemotors (Oct 1, 2010)

Good transformers are rated to 200C, about 400 degrees F,
i.e. pretty freekin hot, which means they can be air cooled pretty effectively when the temp difference is so large.




evmetro said:


> I have an EMW 12000 that I use to charge a pack @127 volts, and the output toroid gets pretty toasty with it at that lower voltage higher current configuration. On a higher voltage pack, the input one builds up more heat, and on lower voltage packs the output one builds up more heat. I am going to have my output toroid rewound so that it does not get as hot, but I was wondering if there were water cooled ones available so that I could use the same specs as the one that is in there without overheating it. I googled them and saw a few possibilities, but I don't have the technical knowledge to know what the drawbacks would be or if anybody here with knowledge of how the EMW works had any thoughts on this idea?


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## evmetro (Apr 9, 2012)

I have come to a general understanding of heat to understand that heat generally means waste or lower efficiency of various things when creating heat is not the main objective. I suppose that if excessive heat was transferred out into the atmosphere, it would still be wasted energy, but I don't understand transformers enough to know if running cooler would make them more efficient. An increase in efficiency that would make the whole system more efficient after the waste heat was written off.


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## Sunking (Aug 10, 2009)

evmetro you can use any kind of oil you want, it just has to be light thin oil. Shop around for TRANSFORMER OIL and see if you can find small quantities. If you have a friend in the electric utility industry they can get all youi want free as they buy it by tank loads. You can even use BABY OIL which is scented mineral oil. 

All oils as most petroleum distillates are non-conductive, even veggy oils. You can even put them is diesel fuel to burn them in a pinch.


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## arber333 (Dec 13, 2010)

Let me join in from experience and some from my profession. Iam ME aerospace, so they gnaw us with fluid dynamics pretty much .

If you want efficient machine ie. not heavy... you use cooling medium which surrounds the machine - the air in our case. So like water air flows and takes with it temperature, albeit at the lower rate than water. 
However there are some things that we can do with ait cooling that water cant. 

Air lowers temperature by speed along surface. So we must provide good surface and fast airflow NOT plenty of airflow! Water on the other hand lowers temperature by its dC thermal coefficient and radiation, so speed is not required, just nice even flow.

I suggest aircooling since it is the cheepest and more reliable since it has less parts.

1. We have to make an air slot that would speed up the air along our toroid to cool the windings. 
2. I have made a round socket for toroid on my lathe out of Novilon material. Any material that is nonconductive and can stand 150°C would do.
3. At one end this fixes to charger housing with the opening for fan on one end and trough the other end we insert our toroid and fit it inside. We created a duct.
4. I suggest fast fan sth. over 3500RPM. Since the fan will pull air trough this duct air will flow just on the surface of toroid and in effect cool wiring. I believe at 20kHz we cool the wire not the core!

This variant of cooling is very effective and my charger was working at 55A 150VDC output at T1=45°C, i touched inductor (not reccomended) and it was only warm to touch. I kept it there for 3 hours. 
It depends on the outside air temp. When air was 40°C charger was 57°C and kept reducing power. Toroid was still not very hot though.

Here are some pictures of my small single phase 3kW charger. Note inductor is T300 core 55 windings, but for 3phase 8kW charger i use larger T400 core with 42 windings.


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## Ai! (May 9, 2014)

air cooling = dust on all components, and efficiency of cooling will fall. Liquid cooling is closed system and has almost 24 times more thermal conductivity than air.


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## evmetro (Apr 9, 2012)

I am really enjoying this thread, and am learning a lot of stuff. Concentrating the available air like arbor is doing makes sense, and the oil cooling is really neat as well. In the pic below, you can see that my toroids are mounted very close to the coolant pump, so it would be very simple to add the toroids into my existing cooling circuit. The controller and emw12000 charger are both water cooled already, so adding another component to cool would just need a little rework on the hose routing. What would be really slick about oil cooling the toroids, is that I would never have to hear the fans running. I could just get rid of them, and have a more peaceful sounding charge cycle. I was also considering the use of a submerged coolant pump if I made a container for the toroids, so that the pump would be even quieter.


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## psron (Jun 19, 2012)

One option to trying to completely surround your Toroids with liquid, is to sandwich them with liquid cooling plates. If you use a thick & squishy silicone heat transfer pad on each side, and squish it down fairly snug, you can actually get a LOT of the heat out, without the coolant leakage worries.

Get thick pads... maybe 0.2", so that it will go between the wires and touch the core. http://goo.gl/We4fBX
(I applied some pre-filtering of the search results)

Thick pads will also help keep the metal plates a bit away from the cores... so you don't disturb the inductance/performance of them.

Cold plates: http://goo.gl/GpIV17

You can make your own by soldering small copper tubing to copper plates... but you can probably find stuff at computer stores that might work too. http://goo.gl/zqJNU3

Just some ideas....


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## Tesseract (Sep 27, 2008)

The very premise of this thread is flawed. You don't resort to liquid cooling if an inductor is running too hot, rather, you instead choose a different core material with lower losses (e.g. - Magnetics, Inc. "Kool-Mu") or step up to a larger core size.

Powdered iron - which is the material used for the cores in this travesty of a charger - has the highest core losses of pretty much any material out there (and a unique problem - if it gets hot enough it will go into thermal runaway, which is exactly as bad as it sounds) but is often selected anyway either because it is so cheap (a bad reason) or because there is relatively little AC flux swing and/or said swing is at a low frequency (good reason). Unfortunately, the AC flux swing experienced by each inductor in this charger will vary over a tremendous (read: unpredictable) range depending on the combination of input and output voltage and current.

Doubly unfortunately, just changing the inductors to have lower losses, or at least a lower temperature rise, won't solve the other critical/fatal problems with this charger.


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## evmetro (Apr 9, 2012)

Tesseract said:


> The very premise of this thread is flawed. You don't resort to liquid cooling if an inductor is running too hot, rather, you instead choose a different core material with lower losses (e.g. - Magnetics, Inc. "Kool-Mu") or step up to a larger core size.
> 
> Powdered iron - which is the material used for the cores in this travesty of a charger - has the highest core losses of pretty much any material out there (and a unique problem - if it gets hot enough it will go into thermal runaway, which is exactly as bad as it sounds) but is often selected anyway either because it is so cheap (a bad reason) or because there is relatively little AC flux swing and/or said swing is at a low frequency (good reason). Unfortunately, the AC flux swing experienced by each inductor in this charger will vary over a tremendous (read: unpredictable) range depending on the combination of input and output voltage and current.
> 
> Doubly unfortunately, just changing the inductors to have lower losses, or at least a lower temperature rise, won't solve the other critical/fatal problems with this charger.




I am very glad to have your input on this thread. I have not been able to find another charger with the output of this one, and I am very interested in charging very quickly. I am not aware of the other problems of this charger, and at this early stage, and I am quite impressed with the performance of it. My intuition regarding the potential thermal runaway that you mentioned is why I am interested in liquid cooling the inductors. In my case of a lower voltage pack, the output toroid is the one that exhibits the potential of thermal runaway, and on high voltage packs, it is the input one that shows this potential. I do not know for sure that either one will in fact runaway, but my intuition had me adjust my output to far less than its capability. I have come to understand that developing a more appropriate toroid requires an EE background and experience that I do not have, but if I can cool these ones that are performing beautifully other than the heat that has me worried, I would end up with the capability of turning it up to full potential. Right now, the charger runs as quietly as my IPad, other than the fans, and I suspect that it would be even more peaceful if I could eliminate the toroid fans. 

What are the other problems with this charger that I have not encountered yet?


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## PStechPaul (May 1, 2012)

I overlooked this thread until now, and I have some ideas that have not been mentioned or explored. A toroid produces the most heat (from copper losses) in the center, where the conductors are bunched together and there is less surface area for air flow and transfer of heat. This problem is compounded by the mounting method with a thermally insulating and air-flow-blocking chunk of plastic through the hole.

If this is the only problem, it may help to use an "omega" bracket around the outside of the toroid, which will allow airflow through the center. The muffin fans direct air on the outside surfaces of the toroid, with little in the center, so a blower with a small air outlet might direct a much greater amount of air where the heat is being generated.

If you want to use fluid cooling, you can put a piece of copper pipe through the center of the toroid, and secure it in place with heat-conductive epoxy. The magnetic field will induce a voltage in the pipe, but it won't affect anything if there is no current path. So use hose barbs and rubber or plastic tubing to connect with the cooling fluid circuit. The small amount of voltage probably will not cause significant current flow through the coolant, but I don't know what its conductivity is, and it could increase if it becomes contaminated or ages.

If the heating is primarily from copper losses, it should increase by the square of the current, and you might be able to see it with an IR imaging gun, or non-contact IR temperature gauge.

The toroid is used as an inductor, and the powdered iron is an appropriate material because of its distributed air gap. Powdered iron does have higher losses than ferrite, but to avoid saturation with DC current, an air gap would be needed, and it is difficult to incorporate in a toroid.

Core losses are based on the volt-seconds applied to the core, and are highest under no load conditions, all else being equal. But this design uses a fixed frequency and variable duty cycle to achieve the output current required, and there is no mechanism to detect saturation. This is a potential "fatal flaw" in this design.


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## Tesseract (Sep 27, 2008)

PStechPaul said:


> ...A toroid produces the most heat (from copper losses) in the center, where the conductors are bunched together and there is less surface area for air flow and transfer of heat.


True, *if* the toroidal inductor has a multilayer winding (ie - fills most of the available window area); for various economic and electrical reasons it is usually optimal to only wind a single layer on a toroidal core. If you need more turns then you should consider a larger core or a different core shape (particularly at higher power [e.g. - above 1kW]).



PStechPaul said:


> If you want to use fluid cooling, you can put a piece of copper pipe through the center of the toroid, and secure it in place with heat-conductive epoxy. The magnetic field will induce a voltage in the pipe, but it won't affect anything if there is no current path


Setting aside the practicality of such a solution (which is highly debatable), it is critical that the coolant used be totally non-conductive, otherwise it will create a shorted turn that kills the inductance (by effectively removing the core from the circuit, leaving only the leakage inductance of the windings).



PStechPaul said:


> The toroid is used as an inductor, and the powdered iron is an appropriate material because of its distributed air gap. Powdered iron does have higher losses than ferrite, but to avoid saturation with DC current, an air gap would be needed, and it is difficult to incorporate in a toroid.


Gnf... Firstly, gapped ferrite and powdered iron aren't the only two choices of core material that are appropriate for inductors which must sustain a DC bias (aka "chokes"); there are numerous other core materials such as Kool Mu, Metglas, XFlux, etc. Usually there will be several different core materials, winding configurations and shapes that could be used in any given application so selecting the optimal combination depends a lot on other considerations like budget, available space/area, efficiency, etc. Secondly, you don't gap toroids, but especially not ones made of ferrite (two reasons: intense fringing flux effects and ferrite, in particular, is very brittle).



PStechPaul said:


> Core losses are based on the volt-seconds applied to the core, and are highest under no load conditions, all else being equal....


Core losses in an inductor/choke are proportional to flux swing *and* frequency, which is another way of saying volt-seconds times repetition rate, but such losses are always highest at *maximum* load, regardless of topology.


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## PStechPaul (May 1, 2012)

I am not a magnetics expert, but some recent reading of some material as listed in my thread on inductors and magnetic principles gave me more information and countered some things that I (and others) assumed. For a transformer, core loss is based only on the applied frequency and voltage, and not on the current through the windings or the power being transferred. And in a real-world scenario, the voltage will tend to drop with increased load due to source impedance and waveform. Resistive losses in the copper windings account for all additional power dissipation and heating. Here are some links:
http://www.micrometals.com/material/pc_coreloss_txt.html
http://www.mag-inc.com/design/design-guides/powder-core-loss-calculation

Of course, an inductor is rather different, since the applied voltage is a function of load, and a significant and variable DC component is always present (at least in most buck converters). 

Toroids rarely use a fixed magnetic gap, so materials such as powdered iron with a distributed gap are used. But it is common practice to utilize air gaps in an E-core or C-core design. It might be interesting to compare the size, weight, cost, efficiency and performance of a powdered iron toroid to an e-core ferrite with an appropriate gap. 

As for the effect of the conductivity of coolant through the hole of a toroid, it depends on the concentration of glycol as well as the TDS (total dissolved solids). I found this:
http://blendtech.biz/antifreeze-information/conductivity-antifreeze-coolant.html










The literature value for conductivity of ethylene glycol is 1.07e-6 mhos/cm, and can be 1000 times less for triethylene glycol:
http://www.dow.com/ethyleneglycol/about/properties.htm

Low conductivity coolants are available:
http://www.brweldingsupplies.com/miller-low-conductivity-coolant-043810/

There are some alternatives for electronics cooling.
http://www.electronics-cooling.com/2006/05/an-overview-of-liquid-coolants-for-electronics-cooling/

Here is a list of conductivity of various materials:
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity

Copper 1.68e-8 ohm-meter or 0.0168 uOhm-cm

Sea water 2.0e-1 ohm-meter or 0.002 ohm-cm

Drinking water 2e3 ohm-meter or 20 ohm-cm

De-ionized water 1.80e5 ohm-meter or 1800 ohm-cm

Glycol 1.07 mhos/cm or 935,000 ohm-cm

Resistance = Resistivity * length / area

So a hose with ID of 0.01m (0.4") and length of 1 meter filled with sea water would have a resistance of 2546 ohms, and with a maximum of about 5 volts/turn, the current would be about 2 mA. If it were copper, its resistance would be 213 uOhms and 5 volts would cause a current of 23,000 amps.

Feel free to check my math. I could easily have made some mistakes in conversion of units.

I don't think it will be a problem. But if you are really concerned, you could use two or four smaller pipes with alternating opposite flow direction and there will a net zero induced voltage.


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## dcb (Dec 5, 2009)

the two methods that seem most practical are mineral oil (folks run their PCs in aquariums full of it), and taking better advantage of PV=NRT with better air ducting/venturi around the toroids. With the former you only have to hose out the radiator on occasion, and less worries about puddles, but the latter is a lot less complicated/more cost effective.

The military has switched to Aliphatics (i.e. mineral oil) for a number of purposes and they are fairly harmless:
"aliphatic PAO-based fluids have replaced the silicate-ester fluids in a variety of military electronics (and avionics) cooling applications in the last decade."

the PC thing is a little spastic, but there it is, power supply and all.
http://tinyurl.com/q5cfnx5


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## steven4601 (Nov 11, 2010)

Great advise has been given already. Stay away from direct liquid cooling until you are in the exotic power densities.

If you are still looking for an economical solution, you have to find out what is heating up the most.

Core ? If possible Increase the number of turns may help to reduce the ripple. 

Copper? More strands of litze wire if it does not fit id recommend going for dividing the current over a 2nd set. I^2 falls of quite nicely with a 2nd set & more surface area.


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