# Looking for a motor controller to implement between a 94V pace battery and a 24V transaxle motor?

#### Julezorz

Joined Apr 10, 2023
2
I have to use a 94V battery to power a 24V DC motor and looking for suggestions on a motor controller that will help with the buck converter aspect and in rush current of the motor?

Im a student so still trying to learn the best way to do this and was told this may be the best approach?

The battery is 94V, 8Ah, 748.8Wh
The motor is 24V, 250W continuous, 380W peak.

#### Papabravo

Joined Feb 24, 2006
20,399
So, the first step in this process is to apply the immutable rule of DC-DC conversion schemes. That is:

The output power will always be less than the input power. Sometimes it will be much less.
So, the battery can supply 94V @ 8A, which is 752 watts. I suppose you might decide that the battery can do this for approximately 1 hour, but let's ignore that for the time being.
for the sake of argument, let's say that we can build a DC-DC converter that is 80%. this means that the available output power will be 80% of 752 or approximately 602 watts. If the motor takes only 250 watts then the battery does not have to supply anything like what it is capable of. Now 250 watts to the motor will require 250 / 80% = 312.5 watts from the battery, this tells me that the battery will last approximately 748.8 / 312.5 ≈ 2.4 hours.

If you can make a converter that is more than 80% efficient you will get longer life from the battery.

One thing you should know. A garden variety DC-DC converter does a really crappy job of starting a motor from a dead stop. The reason for this is that a motor often represents a dead short across the supply and may take sever times it's running current to get started depending on the load and or rotor inertia. It is possible to design a DC-DC converter with excellent transient response, but this involves additional cost and complexity. Are you sure you want to go down this rabbit hole?

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#### Julezorz

Joined Apr 10, 2023
2
I don't want to, but unfortunately, both are required, and I at least need to put together calculations and a rough schematic.

As far as what you mentioned about a DC-DC converter not being well for this job, are there things I can put before or after it to help with this issue?

Or as another approach, would a speed controller such as this help?
https://www.ebay.com/itm/1838675179...4uii40-LBATesW79a4d3pP1vLWHhhUvsDpkNGA0jQNKFk