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Can't find the transformer I need so need to build my own

brandnewb

Nov 30, 2021
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Step 1. Does anyone know where I can find laminated soft boilerplate steel core to buy in Europe?. The bigger the better as I plan to wind the primary and secondary coil my self in various sizes for several use cases.
I do have a 3d printer and can print with non conductive magnetic (iron filled) pla filament once it arrives. Could I simply print the transformer core and have acceptable results?

Step 2. The first use case would be to charge a LifePO4 3.2V cell with 3.6525V at 140 amps to see if it can (test if the cell is up to specs)
As source I have 16 amp 228VAC single phase.

If I give the primary coil 380 winds (760 turns) with 0.4mm enameled copper wire
and the secondary coil 6 winds (12 turns) with 5x1mm (with the ends soldered together) enameled copper wire. Is my math correct in where I should get around 3.65V output minus some losses?

I realize I'll need a full bridge rectifier in between the transformer and the battery cell but if I get stuck there I'll create a separate thread as to focus the topics.
 
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Minder

Apr 24, 2015
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So you will end up with 5v+ after rectification!
Why not just pick up a suitable toroidal version and customize the secondary?
Very easy for these types.
 

brandnewb

Nov 30, 2021
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So you will end up with 5v+ after rectification!
Why not just pick up a suitable toroidal version and customize the secondary?
Very easy for these types.
thanks for the heads up. i guess it takes some trail and error then to get the correct DC output after reification.

i'll look into toroidal transformers. have not learned about those yet. thanks for the suggestion

So you will end up with 5v+ after rectification!
Why not just pick up a suitable toroidal version and customize the secondary?
Very easy for these types.
wow, sweet. i just realize this is how a variac works. thanks again for setting me on this path

but am I correct in assuming that it is the diameter of the secondary coil wire that determines the output amp range? The ticker the more amps it can handle?
 
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Minder

Apr 24, 2015
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The transformer core and the secondary wire gauge are all aspects to be considered when sizing a transformer and the relative windings.
Usually stated in (K)Va .
 

kellys_eye

Jun 25, 2010
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Forget using a transformer.

Get a decent lead-acid battery and charger. It will be able to dump 100's of amps into any load you care to attach and regulating from 12V to your desired output is easy-peasy at 12V rather than from some obscure AC source.

If you want to use SMPS you can obtain 5V DC at many 100's amps from used (second hand) ex-server power supplies. I recently obtained a 12V 100A SMPS (ex Hewlett Packard) for $20.

My 12V unit is adaptable to change the output +/- 20% and 5V versions may crank down to the 3-ish volts you need??? There are many projects online that deal in modification of these units.

They can also be wired in parallel for greater output currents.
 

brandnewb

Nov 30, 2021
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can you please give a concrete example of this lead acid charger you are referring to?
 

kellys_eye

Jun 25, 2010
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The 'lead-acid' charger will be anything suited to the battery you use as the SOURCE supply. You can purchase any number of lead-acid battery chargers for different purposes. The key is that the charger only outputs a low current and requires the appropriate time to charge the battery to its full capacity.

A 100Ahr 12V battery charged at 2A will take 50 hours to fully charge. Thereafter the battery can deliver its FULL charge at the maximum rate the battery itself can withstand without damage - in the case of car batteries this can be 1000 amps 'instantaneous' current for a few seconds (i.e. cracking a large car engine in cold weather).

Determine what maximum current you need, for how long and get the right battery for the job (look for the CCA - cold cranking amps - rating) then get teh charger you feel is necessary to recharge that battery in the appropriate time frame.

None of this is 'obscure' technology - readily available, relatively cheap. Don't forget some darned good fuses as protection too!
 

brandnewb

Nov 30, 2021
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Perhaps I missed it in your initial suggestion but I need a 3.6V power source at 140 amps. I'll admit that I am quite inexperienced so it's possible that you are suggesting that otherwise I'd like to focus on what I need.
 

kellys_eye

Jun 25, 2010
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What I am suggesting are a few simple ways to achieve what you require. Your own idea to make a transformer is, in my opinion, far too involved.

The easiest way to get a high current source is from suitable BATTERIES and lead-acid (i.e. car batteries) are cheap, plentiful, easy to recharge and capable of delivering a THOUSAND amps if you want them to.

The next easiest source is from something ready-made (commercial) hence the suggestion you use ex-server power supplies. They are ready-built, mains powered, have built-in protection, can be paralleled (to any required output current you seem to need) and are readily modified to change from the 5V they normally output to the 3.xxx volts you want to use. You will have to develop an external means of varying the current though - not impossible and potentially accessible through the existing circuitry in the server PSU if you know what you're doing.

Your own transformer-derived idea would, of course, require the relevant regulation and control circuitry to get the necessary voltage and at the LIMITED CURRENT you want (unlimited means a very high potential for catastrophe and physical injury) so the voltage/current regulation will be needed regardless of the voltage source you use hence the suggestion for using car batteries.

You are (I hope) aware of the dangers involved at these currents? Burns, explosions, acid (if you use the battery method), exploding PSU's if you don't modify the server PSU properly, exploding LifePO4 if you get it wrong etc etc? This is not really something the 'unskilled' should be attempting but if you want to go ahead then the two methods I suggest are (probably) the easiest way to get high current sources.
 

brandnewb

Nov 30, 2021
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Thank you for the elaboration, While I wait for the torodial transformer to arrive I'll see if I can find my old server gear if my wife has not disposed of it already and take a look at those PSU's

And also thank you for the warnings regarding safety. I am for sure a newcomer to the field and can easily make a mistake here and there.
The situation is that I need to see if the cells I bought are really up to spec as they are from this popular web site from the east and one never knows. If they check out I can then get much more of those at a reasonable price where I would otherwise have to get a second job if I get them from a reputable source.
 
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kellys_eye

Jun 25, 2010
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The first use case would be to charge a LifePO4 3.2V cell with 3.6525V at 140 amps

I'm not sure with LiFePO4 cells but charging them at 140A seems somewhat excessive - is this not the maximum discharge current?

Can you provide a link to the actual battery being used or some data regarding its manufacture?
 

brandnewb

Nov 30, 2021
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please forgive me if not allowed to post a link
https://www.aliexpress.com/item/1005002637835515.html

In case the link gets deleted I'll also post the specs
Product name: lithium iron phosphate cell(3.2V 280AH LIFEPO4)
Typical capacity: 280Ah(25±2℃,fresh cell, 0.5C discharge)
Minimum capacity: 280Ah(25±2℃,fresh cell, 0.5C discharge)
Internal impedance: 0.1 ~ 0.3mΩ
Nominal voltage: 3.2V
Dimensions(L*W*H): 174*72*203mm
Shell Material: Aluminum
Weight: 5.3 ± 0.1 kg
Recommend constant current: 280A (1c)
Discharge end voltage: 2.5 v
Recommend constant current: 140a (0.5c)
Charging voltage: 3.65 v
Maximum continuous discharge current: 280A (1c)
Life cycle (80% dod): 25℃0.5C/0.5C 80% ≥3500Cycle &
25℃0.5C/0.5C 70%≥4000Cycle
Standard charge temperature: 25±2℃
Absolute charging temperature:0~55℃
Absolute discharge temperature: -20~55℃
Operating:-20~60℃


14 of the 16 cells turn out to be great. the other 2 I am not sure about so I want to test them a bit harder this time.
 

kellys_eye

Jun 25, 2010
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Well that eases my mind somewhat! Here's me thinking they were the plastic shrink-wrapped things you stuff in a drone! Looks more like a 'battery wall' type device.

1C seems awfully high rate to charge - not in an electrical sense but in a 'why the heck would you want to' sort of way, not to mention 'what makes you think you can' kind of way!

If this is intended as a store for solar/wind then getting the charge rate into the 100's of amps range will be a sight to behold! I'd be satisfied with a test for max discharge rate (against temperature), charging the devices at a more reasonable - not to mention achievable - rate.

IMHO trying to charge them at the stated max rate (1C) is pointless if you're not going to do this repeatedly anyway in normal use.
 

brandnewb

Nov 30, 2021
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max charge current is .5C (140 amps)

And I am building a 3 phase alternator to go with a DIY VAWT (2x3m) that should output about 180VAC at 60 rpm if I get my design right. Then transforming that to 3 x 48VAC then full bridge rectifying it to 52VDC.
The turbine calculations (https://www.omnicalculator.com/ecology/wind-turbine) boil down to 1.2KW at 11m/s wind which is quite common in my area. So 1200/48 = 25 amps.

When it is really windy at 25m/s then we are looking at 14.8KW. 14800/48 = 308 amps so I will then need to use a dump load to heat up a water buffer.

disclaimer btw. I am not good at math at all and I know even less of the involved formula's so if I am wildly misguided please let me know
 
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kellys_eye

Jun 25, 2010
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Your maths is probably ok - you might be mistaking the wind power for the actual available power though. For the VAWT with 1.223kW available WIND POWER the actual output (electrical) is 0.349kW so at 48V is 7.27amps (maximum 4.9kW or 100A). You forgot to factor the efficiency in (or, rather, inefficiency).

Load shedding would be required any time your battery is fully charged and there's no where for the surplus to go so having a proper BALANCED system is critical.
 

brandnewb

Nov 30, 2021
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Shall I try hooking this up?
upload_2022-2-3_16-47-52.png
It's a 3d printed transformer core using iron filled filament. the core therefore is ferromagnetic but not conductive. There are 4 parts that are squeezed together so that it can be disassembled for another configuration.
For this use case I've used 63 winds of 1mm enameled copper wire on the primary side and a single wind of 50mm2 wire on the secondary side.

If no objections then I am going to try it.

primary input is 230VAC at 50HZ so I am hoping I have an output on the secondary of 3.65VAC at 50HZ.
 

Alec_t

Jul 7, 2015
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63 winds of 1mm enameled copper wire on the primary side
I think you'd better have a fire extinguisher handy. Mains primaries normally have a LOT more turns than that. Im sure some other member here will have the figures/maths.
 

brandnewb

Nov 30, 2021
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I could double te winds to 126 and then do 2 winds on the secondary. theoretically that should also give an output of 3.6VAC

Or I could do a 10 fold of turns (630) on the primary with 0.4mm enameled copper wire and 10 turns on the secondairy
 
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Harald Kapp

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The seemingly primitive transformer is more complex than you may think. Here's a site that shows how to design a DIY transformer.
Apart from core material, windings etc., there's the matter of safety (insulation, creepage distances etc.).
Better buy a well made off the shelf transformer.
Can't find the transformer I need so need to build my own
What are your requirements? What is so exotic you can't use a commercial product?
 

brandnewb

Nov 30, 2021
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Thanks for the heads up. I'll be sure to read up on it.l
I am looking to transform 230VAC 16 amps to 3.65VDC at 140 amps. Later down the line I am looking to transform 230VAC 16 amps to 58.4VDC at 140 amps.
I could not find anything commercial that does this
 
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