Dual voltage dc system - 12V and 24V.

Thread Starter

Rlbooms

Joined Jan 22, 2021
28
So I have a machine that runs on 12v dc ...engine/alternator .......140Amp alternator to compensate for all the devices that draw current.
I need to replace a 12v motor with a 24v motor to gain the required torque I need for it to function properly.

Trying to figure out how to set this up......thought about replacing the existing alternator with a 24v one and some sort of dc converter to power the 12v side of things and the 24v alt and new batteries power the 24v motor (motor amp draw is about 35 amp)

Can not find any converter that has a high enough power output to supply the 12 volt side (140 amp on the alternator.....Company used a 120amp one and it was not enough to keep the battery charged with all the use of the hydraulic pumps that run on the system over time)

I have one that puts out 70 amp continuously.....could I run 2 of them in parallel to get 140 amp supply?

I also thought of a dual voltage alternator...but they are just way to expensive....

Can anyone help me to come to a workable solution?

ps- I have to keep the motor as 24v as I need to keep the form factor of the motor and I have researched motors quite extensively....
 

MisterBill2

Joined Jan 23, 2018
17,790
Two choices, it seems: Trade that 24 volt motor for a same horsepower 12 volt motor, OR add a 12 volt battery and a scheme that charges the second battery whenever the 24 volt motor is not running. That scheme could keep the battery adequately charged, maybe. It is a way that could provide the 24 volts power.
 

Thread Starter

Rlbooms

Joined Jan 22, 2021
28
So the system has a 12v motor... Max torque you can get in that motor frame...... Can not change motor frame... But found the same one in 24v which gives the torque needed to run properly.
Two choices, it seems: Trade that 24 volt motor for a same horsepower 12 volt motor, OR add a 12 volt battery and a scheme that charges the second battery whenever the 24 volt motor is not running. That scheme could keep the battery adequately charged, maybe. It is a way that could provide the 24 volts power.
 

MisterBill2

Joined Jan 23, 2018
17,790
OK, so it looks like adding a battery will be the path to take.
So now there are some questions to answer. The first question is about running time for the 24 volt 70 amp motor. The second question is how much current is left over while running all of those other motors while the 24 volt motor is not running. AND, how much other current is drawn while the 24 volt motor is drawing 70 amps.
The reason is that all of the energy used from both batteries while that motor runs must be replaced when it is not running, otherwise batteries will slowly run out of charge, and you will have at least one dead battery. The total used must not be more than the total returned.
 

twister007

Joined Feb 29, 2012
81
So I have a machine that runs on 12v dc ...engine/alternator .......140Amp alternator to compensate for all the devices that draw current.
I need to replace a 12v motor with a 24v motor to gain the required torque I need for it to function properly.

Trying to figure out how to set this up......thought about replacing the existing alternator with a 24v one and some sort of dc converter to power the 12v side of things and the 24v alt and new batteries power the 24v motor (motor amp draw is about 35 amp)

Can not find any converter that has a high enough power output to supply the 12 volt side (140 amp on the alternator.....Company used a 120amp one and it was not enough to keep the battery charged with all the use of the hydraulic pumps that run on the system over time)

I have one that puts out 70 amp continuously.....could I run 2 of them in parallel to get 140 amp supply?

I also thought of a dual voltage alternator...but they are just way to expensive....

Can anyone help me to come to a workable solution?

ps- I have to keep the motor as 24v as I need to keep the form factor of the motor and I have researched motors quite extensively....
A 12V alternator can put out 24V with a regulator that you could build.
 

MisterBill2

Joined Jan 23, 2018
17,790
Certainly changing the field voltage to produce 24 volts can be an option, that I had not considered. Then the two batteries could be in series to power the 24 volt motor, and when the second battery rached some high charge level the alternator can switch to just charging the one 12 volt system battery and supporting the loads on that battery. So the big additions will be a relay to move the charging connection and a smart charge control system that moves between charging both to top off the second battery, and the rest of the time just charging the 12 volt battery and supporting whatever loads it has. THAT will be complex but quite doable. I guess.
 

Thread Starter

Rlbooms

Joined Jan 22, 2021
28
A 12V alternator can put out 24V with a regulator that you could build.
Any instructions on that?

More info....
Current 12v motor is rated at 60 amp and is pulling over 70 (no no problem with motor).... Has 25 in/lb torque
New 24v motor pulls 38 amp and has 36in/lb torque.
Motor is on a saw mill and runs the debarker blade..... On for 20-30 sec... Then off for over a minute or more
Manufacture uses a 140 amp alternator to stay ahead of charging.

Would like to know how to convert alternator to 24v and know how many amps it could supply
 

Thread Starter

Rlbooms

Joined Jan 22, 2021
28
OK, so it looks like adding a battery will be the path to take.
So now there are some questions to answer. The first question is about running time for the 24 volt 70 amp motor. The second question is how much current is left over while running all of those other motors while the 24 volt motor is not running. AND, how much other current is drawn while the 24 volt motor is drawing 70 amps.
The reason is that all of the energy used from both batteries while that motor runs must be replaced when it is not running, otherwise batteries will slowly run out of charge, and you will have at least one dead battery. The total used must not be more than the total returned.
What about using the scheme in this photo?
 

Attachments

LowQCab

Joined Nov 6, 2012
3,936
The Schematic will not work as there is nothing to charge the second Battery.

The Voltage currently being supplied to the 12-Volt-Motor
probably "sags" quite a bit when under full-Load.
This will substantially reduce the amount of Power available from the Motor.

With the proper sizes of wiring,
the Voltage available to the 12-Volt-Motor should never drop below around ~14-Volts.

Probably the first thing to do is to replace the Brushes in the existing 12-Volt-Motor,
then see if that makes a performance improvement.

The second step would be to replace the Cables to the Motor, then test again.
The minimum size of wiring should be 4-Gauge Automotive Starter-Cable.
If the Motor is more than around ~6-feet from the Battery,
then 2-Gauge Automotive Starter-Cable is recommended.

4-Gauge Automotive Starter-Cable is also required from the Alternator to the Battery.
Use 2- Gauge if the run is longer than about ~6-feet.

If the Machine is Diesel-Powered, ( or a low-rpm Gas-Engine ),
installing a smaller-diameter Alternator-Pulley may make a huge difference
in the Power available from the Alternator when under heavy-Loads.
The Alternator will not supply it's full rated Current at low RPMs,
it may produce much less than half of it's full rating at Idle RPMs.

Taking care of all of these very important details may alleviate the need for a more powerful Motor.

Just in case, list the 12-Volt Loads,
other than the High-Current-Motor being discussed here,
that are normally powered by 12-Volts as part of the complete Machine.

.
.
.
 

MisterBill2

Joined Jan 23, 2018
17,790
What about using the scheme in this photo?
That would be the discharge connections for using the 24 volt motor at the same time as the 12 volt battery is feeding the 12 volt motors. Because the drain on the 12 volt battery is greater, it will need charging even when the second battery is charged up. So there will be a need to switch both charging connections and voltage regulators between the two batteries. Probably that can be done by just sensing the voltage on the top battery, the one feeding the 24 volt motor. The exact logic will require some detailed considerations.

There IS INDEED AN ISSUE with this scheme, which is heating of the rotating field coil on the alternator. I do not have a solution for that potential problem.
If it is possible to mount a second alternator on the present engine then the whole project could be much simpler. Perhaps the TS can comment on that.
 

LesJones

Joined Jan 8, 2017
4,172
If the engine has enough power could you add a second 12 volt alternator and use the output from that to charge the second battery that would be in series with the original battery ?

Les.
 

MisterBill2

Joined Jan 23, 2018
17,790
If the engine has enough power could you add a second 12 volt alternator and use the output from that to charge the second battery that would be in series with the original battery ?

Les.
That is a possibility, the one challenge being that the second alternator output will need to be isolated from the alternator frame, because the second alternator charging the second battery in the system is 12 volts above frame ground. An alternator with external rectifiers would have no problems with it.
 

LesJones

Joined Jan 8, 2017
4,172
MisterBill2, Good point. I had not considered the problem of an automotive alternator having the negative connected to ground. I don't know if it would be possible to modify the alterantor to have a floating negative output.

Les.
 

MisterBill2

Joined Jan 23, 2018
17,790
Dual alternators would assure against one of the batteries running down gradually. AND it would be much simpler to integrate. Except for adding another alternator.
All that is needed to remove the frame connection from the alternator negative side is to provide three suitable external diodes connected in place of the ones tied to the frame.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
MisterBill2, Good point. I had not considered the problem of an automotive alternator having the negative connected to ground. I don't know if it would be possible to modify the alterantor to have a floating negative output.
Les.
On a typical field regulated alternator, the regulation is totally isolated from the 3ph rectified output?
 

LowQCab

Joined Nov 6, 2012
3,936
On General-Motors-Alternators it's not terribly difficult to isolate both the
3-Phase-Field-Windings, and the Rotor-Winding,
but this project is getting extremely complex just for
the sake of speculating on how it might be
accomplished with 2 Batteries and 2 Alternators, and a new, more powerful, wrong-Voltage-Motor.

The problem solving needs to be concentrated on adequate Machine performance.

Are the Cutters of the Bark-Removal-Mechanism reasonably sharp ?, ( broken/missing teeth ) ?

Is the Motor completely worn-out ?

Are the Cables or Solenoid degraded/corroded/damaged ?

Is the Battery worn-out, or does it have corroded Terminals/Connectors ?

This Machine most likely performed just fine when it was new .......... what has changed ?????
.
.
.
 

Thread Starter

Rlbooms

Joined Jan 22, 2021
28
The system is a woodmizer saw mill.
It is a new system and I have had the company replace the motor..... I in my knowledge of mechanical and electrical things... An 100% sure the motor is undersized for the application.... One woodmizer tech tells me they have lots of issues with it and another tells me not many at all....
I will try to get back out there this weekend and get the wire length and gage.
It is a diesel engine and runs AR about 3k rpm and idles at about 1500 rpm
Uses a DC hydraulic pack to move clamps and such...... Very little amount of time... Engine at idle....
Then when you cut..... The engine kicks in and blade starts, DC motor move head forward... (amps..???)
Debarker turns on..... And you cut a slab of wood.... End of cut engine returns to idle... Debarker shuts off... DC motor returns head to start point.
Adjust log with hydraulics... And repeat.
In there engineering they came to a 140 amp alternator to stay ahead of DC discharge..... A 120 amp did not work.

I will put on some pics first chance I get for you to see...
 

MisterBill2

Joined Jan 23, 2018
17,790
OK,so it seems like the load at high power is less than a quarter of the time. So it could possibly work to just switch the alternator to 24 volts to recharge both battery packs in series as required,
But it also seems like the big effort will be to provide both battery and alternator power to the 24 volt motor. What powers the log movement during the cutting time? Is that a motor or an engine driven function?? If the 24 volt motor is the only one driven during a cut then it might simply work to have the alternator plus battery drive and charge at the same time. Maybe.
 
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