# 240v - 24v Transformer & Rectifier driving 3hp 24v Motor

#### JBASport

Joined Jan 15, 2019
33
I have a hydraulic platform that uses a bank of batteries supplying a 24v DC 3 HP motor that drives the hydraulics. I want to be able to introduce a 240AC to 24AC transformer, then rectify the current to 24v DC. I have acquired the transformer & rectifier (hopefully advice on the sizing/rating when I bought them will be sufficient for the application). I cannot seem to find any data for the transformer or rectifier if anyone can help?
The Transformer is a Tranilamp 3kva (see picture) and the Rectifier is Westcode 24v 120amp (see picture) Thanks, Terry

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Joined Jul 18, 2013
25,019
Is that the label for the transformer at 3.3kva,? if so, the transformer should be capable.
The bridge also appears capable.

#### JBASport

Joined Jan 15, 2019
33
Hi, yes it is. I found a schematic for the rectifier but it is almost impossible to read (see pic). Also I have attached pictures of the set up I am trying to replace. Where a bank of batteries supplies the power to operate the access platform. I want to have a 240v supply to power the 24v motor & use 2 batteries to supply emergency back up only. The image showing the battery box in situ, is for position only to see if would all fit, as nothing is connected as I am not sure how to do that! Thanks, Terry

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#### LowQCab

Joined Nov 6, 2012
1,931
To simplify the overall concept,
You need to build a 125-Amp Battery Charger,
or to say it a different way,
You need to build a 125-Amp Power-Supply, with a 27.6-Volt Regulated-Output.

What is the Duty-Cycle of this Electric-Pump ?
Must it be able to operate with NO Batteries connected ?
If it will always be attached to the Batteries,
the Charger won't necessarily need to supply the Full-Load-Current of the Pump,
this could seriously reduce the huge Cash outlay that You are about to incur,
and will depend heavily on the Average Duty-Cycle of the Pump.

Example :
The Pump is normally operated for less than 1-Minute, every Hour ........
This means the Pump will have a ~60:1 Duty-Cycle,
so You can safely then employ a Battery-Charger that has a Current capability of
125A / 60 = 2-Amps,
but to be realistic, and cover various losses, that number needs to be at least doubled,
so, 2-Amps X 2 = 4-Amps,
So, a 4-Amp, 24-Volt, Battery-Charger, will handle things nicely with a 60:1 Pump-Duty-Cycle.

Building a 125-Amp Battery Charger .........
For reasonable efficiency, and fewer Heat-dissipation aggravations,
You next need to start with a serious, huge, bank of 36-Volt-Capacitors,
and to properly identify the markings on the Diodes that You already have.

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#### JBASport

Joined Jan 15, 2019
33
The intention is for the machine is to run without the batteries using the 240v - 24v Transformer & the Rectifier. The batteries will only be used in a back up situation with some form of switchover. The transformer is rated at 3kva & the rectifier 24v 120amp. Problem I have is that I bought the rectifier secondhand & although rated to what I told I needed, have no idea on how to connect it as it has several connections, some thick cables and some thin wires (see picture). So not sure what goes where? Any help would be much appreciated.

#### LowQCab

Joined Nov 6, 2012
1,931
"" The intention is for the machine is to run without the batteries
using the 240v - 24v Transformer & the Rectifier. ""

Why ????
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#### LesJones

Joined Jan 8, 2017
3,702
From your picture it looks like it is not a simple bridge with 4 diodes. I think it is an SCR controlled bridge which has two normal diodes and two SCRs The SCRs allow you to control the average output voltage by changing the point on the waveform when the SCRs turn on. The back two devices are the SCRs and the thin wires are the gate connections. you will need to make a trigger circuit to provide a trigger pulse to the SCR gates at the point on the cycle when you want them to turn on. Your last picture shows a trigger circuit for the SCRs and output filtering which uses two chokes which have to be rated for the full output current. The unijunction transistor drives the SCR gates via a pulse transformer which has three windings. This isolates the trigger circuit from the SCRs.

Les.

#### JBASport

Joined Jan 15, 2019
33
Sorry to sound so ignorant but your reply is way above my knowledge! Is there a way I can connect that rectifier simply in series with the transformer? If so, how would I connect? Would I need to include the small wires in the setup? Appreciate your help, Terry

Joined Jul 18, 2013
25,019
Sorry to sound so ignorant but your reply is way above my knowledge! Is there a way I can connect that rectifier simply in series with the transformer? If so, how would I connect? Would I need to include the small wires in the setup? Appreciate your help, Terry
Just to claify, can you indicate if each pair of diode rectifiers are marked on the side and if they show different polarity markings to each other?

#### JBASport

Joined Jan 15, 2019
33
I will check in the morning (daylight) and will get back to you. Many thanks, Terry

#### JBASport

Joined Jan 15, 2019
33
Hi, I have managed to take pictures from all angles of the rectifier, Hope this will help? If you do not think it is suitable, maybe recommend what I should source? Thanks again for your help. Terry

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Joined Jul 18, 2013
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There should be a polarity or more likely a diode symbol on the side of the diodes, with the symbol showing polarity direction.
Or indicate the part No.

#### LowQCab

Joined Nov 6, 2012
1,931
Why do You need to run the Pump without Batteries ?
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#### JBASport

Joined Jan 15, 2019
33
The batteries do need keep their charge for long, so rather have a constant power source rather than have to wait each time to charge the batteries up. Also 100amp batteries are expensive and do not last. Thanks, Terry

#### JBASport

Joined Jan 15, 2019
33
I have taken pictures of the diodes, not sure if that helps? Thanks

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#### LesJones

Joined Jan 8, 2017
3,702
Your pictures in post #15 are not clear enough to read the part numbers on the diode and the SCRs This would enable us to try to find the datasheets for them. I think the diodes will have different part numbers as I believe on one the stud will be the anode and on the other the stud will be the cathode.
From picture 5 in post #11 staring from the left side I will number the devices D1, D2, SCR1 and SCR2 and the heatsinks HS1, HS2, HS3 and HS4
This is what I think the devices and connections are.
D1 is a stud anode diode.
D2 is a stud cathode diode.
SCR1 is a stud anode SCR.
SCR2 is a stud cathode SCR.
HS1 is the negative output
HS2 & HS3 is one AC input
HS4 is the positive output
The two thick red wires from D1 and SCR2 connect together and are the other AC input. These are probably joined on the insulated pillar that is mounted between HS2 and HS3.
The thin red and white wires from the SCRs will connect to the secondary windings of the trigger transformer.
The thing at the top left of picture 5 (And bottom right of picture 8) is a current shunt for measuring the AC input current to the bridge rectifier. (I think the saw slit was for initial calibration of the shunt value.)

Les.

#### LowQCab

Joined Nov 6, 2012
1,931
The batteries do need keep their charge for long, so rather have a constant power source rather than have to wait each time to charge the batteries up. Also 100amp batteries are expensive and do not last. Thanks, Terry
The Charger would never be turned off, and draws very little Current when in "Float-Charge" Mode.
This means the Batteries would be completely 100% charged at all times.
If the Batteries are NOT kept in a completely charged state, they will deteriorate rapidly, and be ruined.
Just having the Batteries available means that You MUST have a Charger connected to them at all times.

With a well designed Charger, 2-normal cheap Car-Batteries should last at least ~5-years.
But if it were my project,
I would purchase the most expensive Batteries I could find,
2- Sealed, Deep-Cycle, Optima-SLA-Batteries will cost You around ~$500.oo, and last for ~10-years. A good 24-Volt, 10-Amp Battery-Charger will cost You around ~$150.oo,
and You MUST have a properly designed Charger in any scenario anyway.

Now, with good Batteries, and the required Charger to go with them,
what would be the purpose of spending another ~$500.oo on a 125-Amp Mains Power-Supply ????? Unless the Pump is used with a Duty-Cycle in excess of ~50% or so, there is zero advantage to the big Power-Supply, and with a Duty-Cycle that high, a High-Current Brushed-DC-Motor like the one You have will be worn-out in about 2 to 3-Months, ( if you're lucky ). . . . #### LesJones Joined Jan 8, 2017 3,702 One other point about building a power supply is it will have to tolerate the starting current of the motor that will be several times higher than the running current. The transformer that you have will probably be OK but the diodes MAY be destroyed by the starting current. You will need to check the ratings of the diodes and SCRs from their datasheets. Les. Thread Starter #### JBASport Joined Jan 15, 2019 33 One other point about building a power supply is it will have to tolerate the starting current of the motor that will be several times higher than the running current. The transformer that you have will probably be OK but the diodes MAY be destroyed by the starting current. You will need to check the ratings of the diodes and SCRs from their datasheets. Les. Thanks for your input Les. The Charger would never be turned off, and draws very little Current when in "Float-Charge" Mode. This means the Batteries would be completely 100% charged at all times. If the Batteries are NOT kept in a completely charged state, they will deteriorate rapidly, and be ruined. Just having the Batteries available means that You MUST have a Charger connected to them at all times. With a well designed Charger, 2-normal cheap Car-Batteries should last at least ~5-years. But if it were my project, I would purchase the most expensive Batteries I could find, 2- Sealed, Deep-Cycle, Optima-SLA-Batteries will cost You around ~$500.oo, and last for ~10-years.
A good 24-Volt, 10-Amp Battery-Charger will cost You around ~$150.oo, and You MUST have a properly designed Charger in any scenario anyway. Now, with good Batteries, and the required Charger to go with them, what would be the purpose of spending another ~$500.oo on a 125-Amp Mains Power-Supply ?????

Unless the Pump is used with a Duty-Cycle in excess of ~50% or so,
there is zero advantage to the big Power-Supply,
and with a Duty-Cycle that high,
a High-Current Brushed-DC-Motor like the one You have
will be worn-out in about 2 to 3-Months, ( if you're lucky ).
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Many thanks for your input. Cheers, Terry