10 Amp power Supply.

[More Coffee]

I'm looking to build another power supply,Ive put together a daisy chain of bits ,parts,assortments..
This will just be a single power supply.
The transformer is your typical step down transformer, that started out as a automotive battery charger that consisted of not much more than two diodes for its guts.
It was rated at 2/10/75 amp..The 75amp was only for intermittent use,the transformer buzz's loud and gets warm just idling in this position..
But 10 amp and it sings along quite well,continuously.
Messing around with the terminals and using a bridge rectifier,I can get 30v DC..I don't expect 10amp @ 30volt
Hence I'm aiming for a power supply that can deliver 15v at 10amp, the rest of the voltage upto 18v is mostly what I'll be using ,but being able Tu pull it down to 1.2volt would be an asset.
Continuously variable current and voltage.
The easy stuff like a few amps of 3.3,5,6,9,12 volt @ 1-3amp are easy to dream up.I have a few lm350's on hand also fixed regulators.
After trolling the net ,cant really find a circuit that fits the bill ,generally the circuits either don't have current limiting,are fixed ,offer only variable voltage or no short circuit protection..
I have various op amps,power transistors,
I kindly ask if anyone has seen or know off a particular circuit ,it would be appreciated if you could slip it by.

 

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https://electronics-diy.com/30v-10a-variable-bench-power-supply.php

Any takers on this schematic?

 

[tronitech]

Looks OK and easy to build. If you don't need 30V then perhaps limit the input to 25V or so (18VAC in) to reduce the power dissipation of the 2N3055 's, you may be able to get by with three. Build the circuit and see how it performs it'll be fairly easy to tweak.

 

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Well 'll take what ever I can get out of what I have. 18volt is common.But more and more the RC group im in, the use of brushless motors, and now, raspberry pi opens up a whole new field ,up to 36v..essentially we may becoming less and less dependant on what vendors can offer..and the posibilities of using of the shelf parts to power more with higher current's are becoming obvious..
In saying that
I have on hand 5 TIP3055's and 10 TIP35C's..
My heat sink is large enough to accomodate at least 7 transistors. At worst I can conjure up a piece of 3/4 aluminum plate from the scrap yard an mill out a bigger one if needed.

Looking over the schematic, I got to thinking Maybe I could use 2 TIP3055's (on a whole seperate heat sink) in a Darlington arrangement in place of Q1 to drive the TIP35C's.

 

[More Coffee]

This schematic looks promising as well....After messing with the other circuit I managed to blow the bottom out of the IC..I went back and forth,i goofed somewhere...it may have more to do with using my power supply instead of mocking up the whole circuit....
Which i'm doing now..
the only difference is the resistors..I have 0R5Ω @20W instead of 0R1Ω..I cant see a 0R4Ω difference being a huge problem...


now in regards to the to the 0R15 resistor..a 50Watt unit..I would need about a 100ft of #12ga wire,or 1ft of #14ga NiChrome.......what to do
Cant find a chart for brass wire or rod..
or would just using another 0R5 resistor be just as good..its not 50watt..but just thinking to myself the tolerance alone of the resistor may make up the difference,closest i have is a 0R1 5 watt....
I dug out a shunt resistor as well ,its rated at 200amps..talk about over kill, 75mv type.. Am i right in thinking i can use this on my homemade ICL7106 ammeter...with a little more calibration of course..

 

[KeepItSimpleStupid]

More Coffee:

I have this **broken link removed** VERY USEFUL power supply. When you combine the cord and the adapters, it really can't be beat. I think it was an LM317 based power supply with selectable windings on the transformer therefore it minimizes power dissipation.

The DC adapters just don;t cut it for transistor portable radios (remember those). This one that I have is is on 24/7.

I do have a selectable 0-32V, 10 A linear supply (Harrison Labs 8xxC, I think, that I bought for $15 back in the mid 80's. Huge and heavy. It uses a bank of transistors in parallel and a selectable tap transformer. Hence it says selectable. The front panel control is a screwdriver adjust. Extreme foldback current limiting, so a short doesn;t phase it at all.

 

[fernando_g]

The 0R5 resistor will dissipate 5 times as much power a a 0R1 resistor.

Finding low valued, high wattage resistors is indeed a problem.

I once cannibilized the nichrome heating element of a discarded electric heater. With an ohmeter, I measured the total resistance; and then I cut the elements in segments proportional to the required resistance.
As long as they don't glow red hot, You can tie them down in bronze posts.

The most difficult part was drilling a hole thru the nichrome (for the holding screws), as it is quite hard.

 

[k7elp60]

The LM723 current sense is the voltage drop across the the base/emitter of a NPN transistor. This being about 0.7V I used to use 0.68Ω resistors in parallel. 1 for each amp of current limiting. A long time ago I got a large quantity of them on EBAY. I probably have excess of 100 of them. I would be happy to ship a lot of them to anyone who needs or wants them. They are 5% wirewound by Dale. I just remembered I have a bench supply that is adjustable from 6-14V at close to 9A. It uses a lm723 and a darlington NPN transistor for the series pass and regulators.

 

[Jaguarjoe]

Huge, high watt, low ohm dynamic braking resistors as used in variable speed drives can be purchased pretty cheap if you shop around. MECI has some fractional ohm 500 to 1k watt jobbies for ~$7.00. IIRC, they're about 16" long.

 

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Thanks for the offers and the info,
I think I may have a solution to my problem of the 0.15 ohm resistor...
16GA ,mild steel wire..about 1.96m..of it.OR 1.23m of 18GA .same stuff used to tie re-bar, if my math is right.
It'll make a little heat but..I think it could handle the strain of 10 amps...only problem how does one wrap that much wire with no insulation ..
This is becoming quite interesting..A DIY nightmare ...but interesting..

In the mean time I mocked up the 2nd schematic..it actually works well..but it does not appear that I can turn it down to a few milliamps like 30 or so..it appears to hang around the 200 milliamp range..it well however max out my power supply a 3amp and limit everything in between... it might have to do with using that 0R5 resistor in lue of the 0R15 resistor...

 

[tcmtech]

If you are looking for a cheap but reliable DIY low ohm resistor the spiral wire out of a common school notebook works great!

It takes a bit of trial and error testing to find the right lengths to match your needed resistance of course being they can be any number of gauge and overall length depending on what notebook it came from.

 

[More Coffee]

Now thats a thought!!

 

[More Coffee]

OK..Final stages of testing ..I have an ICL7106 ammeter that I assembled..Using a known resistor this will make it sing..
However the 200A/75mc shunt is another story ,,I cannot even with a multimeter get a reference voltage across the shunt..using a resistor this is a non-issue..

So I got to thinking..Would I be correct in thinking that this 200amp shunt will have a voltage drop of 75mv@ 200amp..because if that the case..Its no wonder i cant get a reference with a 24v---0.5amp load...
And when I think about
it some more..the idea of a 20amp/75v shunt..the whole scale of the mechanics and power transmission becomes apparent..at least in my head..

guess i'm using 3 20watt resistors for my shunt I know it doesn't work that way ,each resistor will have its own characteristic and slightly different value..but its all i have right now..I'll order a 20amp shunt.although i'm a little skeptical of my synopsis of my evaluation

 

[large_ghostman]

how about 10 1 ohm resistors in parallel? might heat up less than wire, not sure of the maths but if wire heats up the resistance lowers? so using wire would give inaccurate readings?? or am i wrong again??

 

[More Coffee]

Resistance increases with heat.

.that generates more heat untill the device either cut out,shorts out,fries,catches fire, blows a fuse or gets hot enough that it will no longer conduct at this point the conductor may have suffered damage from the annealling of the alloy and will no longer function as it should.

A long enough wire ,of the appropriate #GA would suffice.

 

[large_ghostman]

well i was almost right

 

[tcmtech]

So what part of the math relating to low ohm resistors and the relative voltage drops and resulting wattages are you having trouble with?

What referance voltage do you need at what amp level?

 

[More Coffee]

my power supply doesnt work..which wire is wrong?..
Not with out its problems. I blew the 2N2222....again...and again.. system runs well only if there a slight short it blows, if the load like 3amp it blows..It may have to do with instead of a few 2n3055's i'm asking this transistor to drive 6- TIP35C.
Ive decided to replace it with a TIP29B..its a little higher capacity..

Other problems included the regulator for the auto-fan not isolated..and a wiring issue with the ammeter,When the unit was turned on the volt meter was saying 80+Volt and a 2amp drain..there was nothing connected..and my voltmeter was saying there was only 22.3volt at the output.
Turns out that I had tied all the digital grounds together on the ICL7107 Amp meter.. after debonding pin 30 from pins 32/35..all was normal "Ghost Voltage" taken care of.

Hind sight 20/20 I will ad an additional On/ON switch on the maine..This will allow me to switch from a 2 amp current to the 12amp current on the transformer.
I had thought about using a relay ..but the highest current i have is like 5amp.. a little undersized..Id like 10amp..NC=2amp and the NO=12amp
Such is life..

 

[tcmtech]

You are trying to drive three 2N3055's off of a single 2N2222 and are wondering why it keeps blowing up?

Good lord man do some math on the currents involved with the resective gain ratios for a typical 2N3055 transistor and see what you come up with for input currents needed at their base and what that relates in terms of current and wattages going through that tiny 2N2222!

 

[More Coffee]

No..Im trying to drive 6 -- Tip35c's
I did the math..it was wrong ,I also went by the schematic..

The 2N2222 will work as long as a guy dosent load the system..works great as long as your not trying to drive anything more than a computer fan..

I replaced it with a TIP29B works well now