240v AC to 24v DC 3hp supply

drc_567

Joined Dec 29, 2008
1,156
That's the theory. The reality is that such a large load will knock the tops right off the rectified sine waves and the mean voltage will be right back to 24V - or a little less...
PS: I checked my "3hp" hydrualic pump today - and it too is actually 3kW I made the same memory mistake as you... So I'll be looking for a larger transformer than I had looked for previously as well..... until then, batteries will do.
I found and bought a 200A bridge rectifier a few months ago - ready for when I can find a 3kVA 24V transformer....
@JBA Sport: do you still need a circuit drawing for your connections to replace the battery setup or is it all clear to you now?
... useful to know. The 120 Amp motor current would likely make the use of post-rectifier filter capacitors impractical.
 

jhovel

Joined Jul 9, 2016
31
Here is the basic connection diagram for you.
Rectifier.jpg
Now the more tricky bit: the rectifier you have uses two kinds of diodes, two with their anode on the body - and heatsink - the other two with their cathodes on body and heatsink. There will be markings on the diodes which show you which end is which, and you can see how they are connected by the way the red cables are attached. there are also two flat bars connecting the heatsinks to each other in pairs - they are the other two terminals of the bridge rectifier. Have a look at the diagram above and you should be able to work out which is wich.
The black thing in the mifddle is likely to be a thermistor to monito the heatsink temperatures. If you wan to use that, you will need to make close-up photos of markings for us to help you.
The thin cables are connections for gauges. Keep the ends wel isolated (or trim them off) if you don't want to use them.
You may also consider using a 120 or 125A DC circuit breaker in line with your connection to the hydraulic pump - to protect the rectifier.
Lastly, you could charge the batteries with this circuit, but given the power output, that is risky unless you monitor the battery voltage and charge current visually. To design a safe charging circuit will take quite a bit of effort and expense (for components).because of the large currents involved.
I imagine you have a charging setup already for your current batteries? I suggest you continue using that.
Let us know if you need any more or other information.
Oh, and show us what you end up doing with photos!
 

Thread Starter

JBASport

Joined Jan 15, 2019
33
Brilliant. This is so helpful. I am working abroad at the moment so it will be about 6 weeks before I am home and able to look at getting cracking. Thanks again. Kind regards, Terry
 

RPLaJeunesse

Joined Jul 29, 2018
252
JBASport: DO NOT trim off the small wires!!! The two parts with small wires are 99.9% likely not rectifier diodes, but rather silicon controlled rectifier diodes (SCRs). As such they will not conduct unless the appropriate current is passed in a (control) loop via the two wires. And the current loop for each SCR must be galvanically isolated from the other. The wires are the gate and cathode of the SCR. What is the "appropriate current" to feed into the gate? Depends on the SCR, which should have a part number printed on its ceramic body. Typically a phase control circuit would drive a pulse transformer with dual outputs, one for each SCR. By delaying the onset of the current pulse from the last AC zero crossing the effective duty cycle is reduced, thus reducing the effective output average voltage. So your project just got a lot more complicated. I suggest you promptly involve a local electrical engineer that has dealt with SCRs. Either that or study the now vintage "GE SCR Manual", available online. Only 716 pages to leaf through! (For a picture of a similar SCR see http://catalog.chtechnology.com/item/phase-control-thyristors/scr-studs/t600021504bt? )
 

Thread Starter

JBASport

Joined Jan 15, 2019
33
Hmmm, Not so straightforward for a simple man like me, sadly!
Thanks again for your input though, really appreciated. Regards, Terry
 
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