Hello. In this schematic,


R1 sets the voltage regulation ? How to adjust the current limiting ? Is there missing components ? Is Q2 emitter hooked to R4, R1, RL ?

 

How to adjust the current limiting ?

Q2 starts diverting base current from the pass transistor, Q1, when the drop across R4 starts turning on Q2 (around 0.6-0.7V).

Is Q2 emitter hooked to R4, R1, RL ?

Yes. That arrow is a weird way to indicate a connection.

 

How to adjust the current limiting ?

You adjust the value of R4.
The limit is about (0.65V) / R4.

 

Thanks. Just semantics : the "drop" across R4 could be the 'voltage buildup across R4' , right ?

I hope to find a rheostat to adjust R4 for variable limiting to 5 - 15 Amperes

 

Just semantics : the "drop" across R4 could be the 'voltage buildup across R4' , right ?

Yes. In the context I used drop, it means voltage drop.

 

I hope to find a rheostat to adjust R4 for variable limiting to 5 - 15 Amperes

For that you would need a rheostat that goes from about 0.04Ω to 0.15Ω.

And note that the rheostat must be rated for 15A.

 

$116.00 in stock.

Another option for 1/3 the price is a adjustable resistor. 0.16 ohm

 

Virtually zero drop-out Voltage,
Linear-Voltage-Regulator with Adjustable-Current-Limiting .............
MIC5158
.
.
.

 

Programmable (1.3 to 36V) with 2 resistors (MIC5156/8) Use the adjustable version.

 

That Ohmite 0.5Ω pot is rated for 50W, so the nominal maximum current is 10A.
You might be able to operate it at lower resistance setting with 15A but it would me marginal.