PSU Voltage Adjustment

Thread Starter

JulesP

Joined Dec 7, 2018
383
Thread Starter

JulesP

Joined Dec 7, 2018
383
hi J,
Where did you get that post #37 circuit, its yuk!

This is LTS with just one LM338 to check out the design.
E
E, Your circuit only manages 4A whereas I need it to manage at least 30A which is why my attempt uses 5 x LM338s in parallel. Is that not a way to boost current capacity?

J

ericgibbs

Joined Jan 29, 2010
19,017
hi,
This is the important difference between yours and the posted circuit.
The Vinput is a 18Vac transformer, so 18V * 1.4= ~25Vpk less diode voltage drops.
To get a +12Vdc out the circuit must have at least 15Vdc to 16Vdc input.

E

Update:
Did you see this codicil.

Last edited:
Thread Starter

JulesP

Joined Dec 7, 2018
383
hi,
This is the important difference between yours and the posted circuit.
The Vinput is a 18Vac transformer, so 18V * 1.4= ~25Vpk less diode voltage drops.
To get a +12Vdc out the circuit must have at least 15Vdc to 16Vdc input.

E
View attachment 228102

Update:
Did you see this codicil.
View attachment 228104
Yes I did and, given the language translation on the page I wasn’t overly confident in it which is why I drew it up and sent it for ‘review’.

So how might I construct a regulator type of circuit, as a more efficient alternative to the FET method, that can take my 12V, 25A and let me output 7-9V, 25A? Are there any off the shelf circuit designs I can explore?

J

crutschow

Joined Mar 14, 2008
34,700
I have a PWM power supply that has a nominal output voltage of 12V and a current capacity of 25A continuous.
Your diagram shows a PWM duty-cycle control.
Is that actually available?
Would it be possible to change the range of that control?
Do you have any information on what's inside that supply?

Thread Starter

JulesP

Joined Dec 7, 2018
383
Your diagram shows a PWM duty-cycle control.
Is that actually available?
Would it be possible to change the range of that control?
Do you have any information on what's inside that supply?
I’m using a PWM from RMCybernetics as per the attached pdf and using a primary and secondary power supply as per page 5 of that doc. The reason for that is so I can deliver 12V to the PWM circuit and less than that to the electrolysis cell (ideally 8-10V) hence the need to construct a device to drop some volts at 10-25A.

The secondary supply is from:
inShareplus 12V 41.7A 500W, DC... https://www.amazon.co.uk/dp/B08GKTFJZF?ref=ppx_pop_mob_ap_share

and the primary PSU is a smaller but similar device: https://www.ebay.co.uk/itm/AC-110-2...-/203076666329?_trksid=p2349624.m46890.l49292

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Thread Starter

JulesP

Joined Dec 7, 2018
383
Your diagram shows a PWM duty-cycle control.
Is that actually available?
Would it be possible to change the range of that control?
Do you have any information on what's inside that supply?
It seems my request is too challenging a task so I will have to buy a 9V supply off the shelf. Make's life simpler!

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