may I please invite readers of this thread to join me here?
https://forum.allaboutcircuits.com/...old-usecase-for-380-vdc-battery-packs.186114/

 

Very interesting - if slightly dangerous.

How can I cap the output of the secondary coil at 140 amps?

To answer this original question, what you need to do is add some "leakage inductance". This can be done by adding an air gap in the core but it's usually done by adding a magnetic shunt (with an air gap) across the magnetic circuit.
This is often done in arc welders, microwave ovens and neon sign transformers to limit the secondary current.
For a diagram and a picture of a transformer with an adjustable magnetic shunt see the bottom of this Wikipedia article: https://en.wikipedia.org/wiki/Leakage_inductance
Also see the attached picture.

 

Very interesting - if slightly dangerous.

To answer this original question, what you need to do is add some "leakage inductance". This can be done by adding an air gap in the core but it's usually done by adding a magnetic shunt (with an air gap) across the magnetic circuit.
This is often done in arc welders, microwave ovens and neon sign transformers to limit the secondary current.
For a diagram and a picture of a transformer with an adjustable magnetic shunt see the bottom of this Wikipedia article: https://en.wikipedia.org/wiki/Leakage_inductance
Also see the attached picture.

hahahha I get soooo intimidated when looking at that Wikipedia page. I am a simple man with an even simpler brain. I wish I had a brain that understood (advanced) math

 

Don't worry about the math(s). I don't understand most of it either and I've had a career in electronics design most of my working life! OK, I did some in college but mostly ohms law gets you through!
Just wanted to point you at the pictures.

 

To answer this original question, what you need to do is add some "leakage inductance". This can be done by adding an air gap in the core but it's usually done by adding a magnetic shunt (with an air gap) across the magnetic circuit.

Please forgive me if I dumb this down too much;
So getting an variable sized air gap in the iron powder core might be of service?
If so then I have to radically rethink a prototyping setup ;(

I think I prefer to first give the LTSPICE route a shot once I have some more time.

 

I changed my mind back again to stepping up step by step in wire size rather than going 35mm2 directly.

I am happy I did because I found that the variac is perfectly capable of outputting more than 8 amps. No growling, no smell, no heat no nothing other than more amps



the wire I have tried in the interim (the wire I recently ordered but did not tell you guys yet it was not 35mm2) is 16mm2. But given that the primary now draws 10.6 amps I am worried about long term effects so I just ordered 35mm2 wire and it will be here soon and then I will try again.

 

In your final design, I strongly recommend fitting something like this at each positive battery terminal, protecting against excessive discharge due to a fault in the connected circuit (say, should the diode/thyristor in the charging circuit fail short circuit, resulting in the secondary winding being directly across the battery).

https://www.ebay.co.uk/itm/18526943...pYBzqSr2GNGmvd2ud0XJ|ampid:PL_CLK|clp:3650466

https://www.ebay.co.uk/itm/12120901...lfO0oDY6O7NMz%2BM%3D|ampid:PL_CLK|clp:3650466

 

I should start to listen to people with more experience than my self every once in a while ;(


35mm2 wire is making life soo much more easy albeit not cheaper



I tripped the circuit breaker in my breaker cabinet so I removed the DT mmeter.

I think 5.5 amsp in primary is well within a comfortable zone.

I will mentally prepare for LTSPICE now

 

You should soon be considering connecting the transformer output (via a diode/thyristor) to see if you have any chance of the set-up doing what you want (charge a lithium battery).

You could consider this diode pack as an option, with the diodes rated at 200A.

https://www.ebay.co.uk/itm/32433204...9RG8SnPyuCAqcuPWI%3D|ampid:PL_CLK|clp:2047675

The diode would only by used to confirm that the transformer can supply the required current into a lithium battery – my proposed control circuit uses a thyristor (switching the gate) to control the charge voltage/current.

You might like to conduct your own search for a thyristor (SCR) having a current rating of at least 150A for use in the final design – but it is likely to be more expensive than the above diode.

 

Do I get one or more?

btw, since the brexit. Buying online from the UK got a whole lot more slow and expensive ;(

To answer this original question, what you need to do is add some "leakage inductance". This can be done by adding an air gap in the core but it's usually done by adding a magnetic shunt (with an air gap) across the magnetic circuit.

I think I might have found new motivation to give this a go.
What about keeping the same toroid but spltting it where the start and end of the primary meet? I can then slide both ends from each other as to create this variable air gap

would this make sense?

 

If you are going to buy a 200A diode, you only need one – as stated it is to see if the transformer has any chance of charging a lithium battery.

In one of my earlier posts, I gave a link to a pack of 5 thyristors for £9.99 – but they were only rated to 55A – again something to buy for development purposes (limiting the charge to 55A).

You could consider buying this; although the seller lists it as a 150A thyristor, the data sheet shows it to be rated at 100A (for practical purposes).

https://www.ebay.co.uk/itm/22261454...a=1&pg=3817808&_trksid=p3817808.c101465.m3507

The above thyristor is probably the type you need (double package), which could be employed to provide the additional safety in the battery charge circuit.

 

ugg. the seller does not ship internationally ;( I'll do some searching then for an alternative

 

I’ve attached an outline design of the front end control of the battery charge thyristor/SCR in an LTspice asc file to give you an idea of how this is achieved.

I’ve not included any details of the control circuitry (a bit more of that later).

The circuit shows the battery under charge (V1) and the thyristor/SCR (U1) and the 12Vdc to power the control circuit – not shown is the secondary transformer winding that is connected to the thyristor/SCR and 0V, also not shown are component values.

In operation the thyristor/SCR gate is switched on by the 12Vdc via R1 and D1. However should transistor Q1 be switched on, then the thyristor/SCR gate will be switched off (switching off the battery charge current). Transistor Q1 is switched on by taking the control voltage low.

The output of the control circuitry (not shown) will go low should the battery voltage reach full charge, or the charge current exceed a preset level, or the battery temperature exceed a safe charging temperature.

It is not worth me showing the control circuitry until you have demonstrated that your transformer can charge the lithium battery – as stated earlier, I think that you will need to increase the number of secondary turns to get a sufficient voltage to charge it. At present your transformer can supply over 100A into a short circuit; having to overcome the battery voltage will require an increase in the secondary output voltage.

 

I finally found a way of running LTS on a linux machine as I do not run windows anymore.

The SCR Control.asc schematic is a bit intimidating but I'll get through it

First would be to find a suitable thyristor

 

Am I correct in assuming that a thyristor is a full bridge rectifier?
In case so I have a 3 phase and a single phase at 100A available

Can I use the single phase to experiment with?

 

Just found a source explaining a bit more.
https://www.ppi-uk.com/news/thyristor-controlled-rectifiers/
Does not seem to be the same thing as far as my understanding goes;(

 

I did find this one
https://www.ebay.com/itm/324699599232

 

Sorry I did not realize this thread had more posts. Somehow I did not get the notification. I just now got caught up from post #23.

I am concerned by what I have read. I was going to quote each time you measured primary amps & volts, and secondary amps & volts, but that is too much work, so I will just summarize what I saw, and maybe you can correct me if I missed something.

I see you keep shorting the transformer output and taking an amps measurement that seems like a promising number for your application (>100A). Then I see you keep un-shorting the secondary and taking voltage measurements that seem also promising (~4V). But never did I see you measure these two values at the same time.

What do you think is your voltage output, for example in this picture from post # 52?

View attachment 264633

You have the transformer output shorted, so your output voltage is 0V!
Your transformer is capable of outputting 3.65V @ 0.00A or 122.8A @ 0.00V (in either case, 0.00W output power), but I have seen nothing to indicate that it can do both at the same time.

It is not my goal to tear down your work; I think it is a really cool idea to use iron filings as a core and I want to see where this goes. But I assume you are doing this for lack of budget and I would hate to see you dump more money into this if it isn't going to work. I would suggest that before going further, you test the performance with a real load and take more realistic measurements to get an idea whether this transformer is going to work.

In order to simulate a load, you need a very small resistance (about 37mOhms to get 3.65V @ 100A) with the ability to dissipate quite a lot of power (~400W). You could get this by putting many resistors in parallel and/or wind your own resistors out of nichrome wire. Or maybe just copper wire. (for example) 2.5 sq mm copper wire has a resistance of 7.41 mOhms per meter, so to get a 37mOhm resistor you could just use 5m of it. It will probably burn up quickly, but maybe slowly enough to take some measurements.

 

I did not know yet how to measure both voltage and current at the same time. I'll get on getting a proper resistor right away

 

One of your rectifier blocks shown in the photo is for three phase (the one on the left), the other is a standard 4 diode bridge rectifier.

Although the ultimate circuit will use a single diode rectification, you should experiment with the 4 diode rectifier (you might be able to use full-wave rectification in the final design if you have a bridge rectifier capable of handling 150A).

The secondary output of your transformer should be connected to the bridge rectifier terminals marked ~ (polarity unimportant), the + marked terminal of the bridge rectifier connected to the battery positive and the – marked terminal to the battery negative.

You will then be ready to energise the transformer and measure the battery charge current. Remember if you try to measure the current with a current clamp at either battery terminal, you will be measuring DC current, which your clamp may not respond to. Therefore you should use the current clamp in the AC (transformer side of the bridge rectifier) – you can take the measured AC current as being the same as the DC battery charge current.

Take great care when doing this as charging the battery in excess of its rating could result in fire/explosion – but I’m betting you won’t be able to get more than a few 10s of amps charge current (at best) without increasing the transformer secondary output voltage (by either increasing the input voltage and/or the number of secondary transformer turns). Good luck!