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converting a high amperage battery to lower amps without reducing voltage on a DC motor.

Ryan Peeters

May 23, 2021
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I have a project that requires a long lasting power supply and 12-24V but the motor will require much much less amperage than the typical 600+A of the battery, or batteries. I'll need to hook up an amp controller setup to make it adjustable but that can only handle so many amps in standard models or items available. How do I reduce the amps and keep the voltage up to power my machine to at least the max of the controller/motor? If I go over the max amps by several orders of magnitude the motor will last about 5 minutes so that is clearly not an option as I want the system to last. Thoughts?
 

Nanren888

Nov 8, 2015
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Give some details of the battery and motor wyou want to use and a few more facts about what you are planning.
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The short answer is "It doesn't work like that". (Depending on the motor and what you want to do.
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So, if you'd like to give some details, someone can likely help you out.
The good news is: If it is just an ordnmiary DC motor, it may be much easier than you think.
 

Martaine2005

May 12, 2015
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I think you'll find the Max current from the motor will be stall/startup current.
After that, the motor should only require what it needs to run.
But that depends on the motor.

Martin
 

crutschow

May 7, 2021
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In most cases, a motor only takes the current it needs, regardless of how much current the power source can provide.

It's like your appliances at home.
You can plug a 100W mixer motor into a socket that's rated for 15A, but the mixer only will take only the amp or so current it needs.
 

Ryan Peeters

May 23, 2021
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The motor that I will be using is going to be likely be a small high torque (100+kgcm) low rpm (max of 60 rpm) and have a max amperage rating that is at most 5-10A and may be as low as to be in the 0.1V-0.001V[1mV] range. it may have brushes or be without them. I should have amperage regulating mechanism that can handle it and even add a fuse set to keep the system from frying but the regulator board will have to be able to handle the high amps of the battery or batteries. I noticed today at the Walmart that the chargers for batteries are more than likely capable of running the the system and are cheaper, smaller and weigh less that the batteries I was considering and deliver 4-8A at max power so that could help to solve the problem as I could use a pre-built board for the regulator knob hardware and save money on the system as well. I also could design the system to be robust and simply have an on/off switch to run at 60rpm always when it runs to avoid the regulator issue.
If the system is simply too hard to make work I may just get a DC shaketable motor and build a simple shakeboard system (angled with graduated hole sets over buckets connected to a set of springs in a frame) sizes to attach to it rather than the more complicated stacked bucket shaking structure that I have planned. (I want to wet/dry sort sand/soil/rocks into different size rocks and the sifted rock free soil or sand.)
 

Ryan Peeters

May 23, 2021
3
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May 23, 2021
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The motor that I will be using is going to be likely be a small high torque (100+kgcm) low rpm (max of 60 rpm) and have a max amperage rating that is at most 5-10A and may be as low as to be in the 0.1V-0.001V[1mV] range. it may have brushes or be without them. I should have amperage regulating mechanism that can handle it and even add a fuse set to keep the system from frying but the regulator board will have to be able to handle the high amps of the battery or batteries. I noticed today at the Walmart that the chargers for batteries are more than likely capable of running the the system and are cheaper, smaller and weigh less that the batteries I was considering and deliver 4-8A at max power so that could help to solve the problem as I could use a pre-built board for the regulator knob hardware and save money on the system as well. I also could design the system to be robust and simply have an on/off switch to run at 60rpm always when it runs to avoid the regulator issue.
If the system is simply too hard to make work I may just get a DC shaketable motor and build a simple shakeboard system (angled with graduated hole sets over buckets connected to a set of springs in a frame) sizes to attach to it rather than the more complicated stacked bucket shaking structure that I have planned. (I want to wet/dry sort sand/soil/rocks into different size rocks and the sifted rock free soil or sand.)
I meant 0.1A... of course.
 

Nanren888

Nov 8, 2015
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frame?
shakeboard?
buckets?
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I really can't tell what you are wanting to do.
Do you want to control the speed of something?
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For DC motors on DC power supply, eg battery or regulated DC power supply.
The short answer for a motor on a battery, or fixed voltage supply, is that the motor will only due the current (amperage) that it needs, so make the voltage right & the rest will look after itself, assuming the power supply is able to supply whatever the maximum is or more.
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That said, motors don't run constantly and uniformly. Startup is harder so it draws more current than free-running. On load, it draws more current than no-load. Heavier load, more current.
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If you want to control the speed, not just let it run as fast as it runs, then , then you must add some sort of controller.
If you need it to run at 60 revs per minute, then some sort fo speed control will be needed and likely speed sensor and feedback.
And yes, having a fuse is a good idea.
 

Harald Kapp

Moderator
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Nov 17, 2011
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will require much much less amperage than the typical 600+A of the battery, or batteries
This is a common misunderstanding that turns up again and again: An electrical power source's ampere rating is the max. current this supply can deliver without shutting down or reducing output voltage. In the case of the battery this means you can draw up to 600 A from the battery while still still having ~12 V output voltage. If you increase the current further, the voltage of the battery will start to fall considerably.
You can attach a 12 V motor directly to the battery without the need for further measures (apart from maybe a fuse to protect from overcurrent). The motor will draw as much current as it requires to operate. A high starting current, then less current during operation, varying with load (high load -> high current and vice versa).
This works exactly the same way you can operate multiple and diverse 12 V gadgets in your car from the same 12 V battery, be it a few mW indicator lamp. a few W for the radio or the kW of the starter. None of these loads has an "amp controller".
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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... I want to wet/dry sort sand/soil/rocks into different size rocks and the sifted rock free soil or sand. ...
My wife had me build a small shaker box using scrap lumber and hardware cloth stapled to the lumber. This was used to separate "river rock" from dirt after an "idiot" in-law dug up the stones and dumped them on our concrete driveway, dirt and all. No motor necessary, we just sprayed water on the rocks and dirt mixture, allowing the dirt to wash away down the driveway while we recovered the now clean stones laying on the hardware cloth.. We only needed to "clean" a few cubic feet of stones for our front-yard landscaping project, and most of them were about the same size.

I can see how you might need something a little more sophisticated if you have a lot of material, and stones of assorted sizes from pea gravel on up in size to sort.

From your description of the torque and speed of the motor you plan to use, I surmise this is a geared DC motor. These are easily controlled with pulse-width modulated DC power, available from hundreds (if not thousands) of Asian sources for "dirt cheap" prices. Or, if you are electronically inclined, you can roll your own. Beware of trying to use an inexpensive Wally World battery charger for this purpose. These are usually unfiltered DC power supplies, good for charging a lead-acid battery chemistry, but impractical for motor speed control because of their excessive ripple.

It would help us to help you if you would tell us WTF you are trying to DO instead of describing your own solution. This particular cat (DC motor speed control) was skinned a long time ago, and there is no need to learn how to do that again. Stacked sieves driven by a vibrator are the usual means to perform laboratory-scale sifting, but these are usually too small or, if of sufficient size, too expensive. Upside, however, is you can obtain sieves that will sift down to the size of talcum powder.
 
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