Stu Summer
100 W
Could I run a 24V ebike motor with my 52V batteries using a buck converter. Is it a danger to the batteries? Can it be done without ALOT of heat? Can you recommend a product?
52V to 24V buck converter?
- Thread starter Stu Summer
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wturber
1 MW
It should work in principle. I'm doing the opposite using a lower voltage and boosting up (36v nominal to 54v operational.) Your big issues will probably be:
1) Getting sufficient power through the converter. The rating of these items can be misleading if your intended use isn't optimal for how they've rated the converter. My converter is advertised as "1500 Watts", but what matters is the amps. At my voltages, the system only passes 20 amps. At 54 volts that works out to 1080 watts. Good enough for my use, but not 1500 wattts. Using this possible candidate converter as an example, the maximum amps output is 20. So at 24v, the maximum watt output is 24*20 or 480 watts. If that's enough power, then you'd be in good shap. Also, I'd assume that you could run a 24 volt system at 28 volts (maybe more?) and might actually be able to get a bit more than 500 watts of usable output.
https://www.amazon.com/KKmoon-Programmable-Constant-0-50-00V-0-20-00A/dp/B077P5943T/ref=sr_1_1?ie=UTF8&qid=1530763960&sr=8-1&keywords=1000+watt+buck+converter
2) Protecting the battery from being overly discharged. With the buck converter sitting between the motor electronics and the battery, they can no longer monitor the battery for voltage levels. You'll have to do that either manually, rely on the batteries BMS, or possibly rely on the buck converter if it has a low voltage cut off. I didn't see that option on the device above, but my step-up converter does have that option.
3) Reporting battery level. If your motor/system reports on battery level, that will become effectively non-functional because the buck converter will always show a "full" battery since the converter will typically provide a constant voltage output. There is a plus to that in that you won't notice a drop in speed due to battery voltage drops.
4) You'll have to deal with possible heat and mounting issues. I have my step-up converter attached to the water bottle mounts on my seat tube. That provides a natural flow of air to cool it down. That said, my converter doesn't seem to generate much heat. It seems like my boost converter is about 95% efficient or so at the voltages and currents I'm using. So that should be about 50 watts of heat at nearly its max output. But frankly, it doesn't seem like I'm ever getting that much heat from it. The converter's cooling fan never seems to kick on. My headlight gets much warmer and it is supposed to be pulling 45 watts ... and it is mounted on the front of the bike with very good airflow. So the lack of apparent heat is a bit of a mystery. But either way, this is something you'll need to be prepared to deal with. Assuming a 95% efficiency, you'll need to make sure you have enough airflow to cool a 25 watt or so heat source.
I can't recommend a specific converter, but the one I linked to above seems like a good candidate. These kinds of things tend to cost more on Amazon than on eBay. But you can typically get a faster delivery from Amazon.
1) Getting sufficient power through the converter. The rating of these items can be misleading if your intended use isn't optimal for how they've rated the converter. My converter is advertised as "1500 Watts", but what matters is the amps. At my voltages, the system only passes 20 amps. At 54 volts that works out to 1080 watts. Good enough for my use, but not 1500 wattts. Using this possible candidate converter as an example, the maximum amps output is 20. So at 24v, the maximum watt output is 24*20 or 480 watts. If that's enough power, then you'd be in good shap. Also, I'd assume that you could run a 24 volt system at 28 volts (maybe more?) and might actually be able to get a bit more than 500 watts of usable output.
https://www.amazon.com/KKmoon-Programmable-Constant-0-50-00V-0-20-00A/dp/B077P5943T/ref=sr_1_1?ie=UTF8&qid=1530763960&sr=8-1&keywords=1000+watt+buck+converter
2) Protecting the battery from being overly discharged. With the buck converter sitting between the motor electronics and the battery, they can no longer monitor the battery for voltage levels. You'll have to do that either manually, rely on the batteries BMS, or possibly rely on the buck converter if it has a low voltage cut off. I didn't see that option on the device above, but my step-up converter does have that option.
3) Reporting battery level. If your motor/system reports on battery level, that will become effectively non-functional because the buck converter will always show a "full" battery since the converter will typically provide a constant voltage output. There is a plus to that in that you won't notice a drop in speed due to battery voltage drops.
4) You'll have to deal with possible heat and mounting issues. I have my step-up converter attached to the water bottle mounts on my seat tube. That provides a natural flow of air to cool it down. That said, my converter doesn't seem to generate much heat. It seems like my boost converter is about 95% efficient or so at the voltages and currents I'm using. So that should be about 50 watts of heat at nearly its max output. But frankly, it doesn't seem like I'm ever getting that much heat from it. The converter's cooling fan never seems to kick on. My headlight gets much warmer and it is supposed to be pulling 45 watts ... and it is mounted on the front of the bike with very good airflow. So the lack of apparent heat is a bit of a mystery. But either way, this is something you'll need to be prepared to deal with. Assuming a 95% efficiency, you'll need to make sure you have enough airflow to cool a 25 watt or so heat source.
I can't recommend a specific converter, but the one I linked to above seems like a good candidate. These kinds of things tend to cost more on Amazon than on eBay. But you can typically get a faster delivery from Amazon.
wturber
1 MW
Here's another buck converter that might be a good candidate. This one seems to be very similar to my boost converter in configuration and has a higher possible output wattage. It looks like it could deliver around 800 watts at 28 volts.
https://www.ebay.com/itm/DC-Buck-Converter-Step-down-20-70V-to-2-5-58V-Power-Supply-Module-30A-800W-/253234957355
https://www.ebay.com/itm/DC-Buck-Converter-Step-down-20-70V-to-2-5-58V-Power-Supply-Module-30A-800W-/253234957355
Stu Summer
100 W
Thank you WTHurber! I appreciate the help and detailed guidance. I have to decide whether to adapt my batteries to the motor or upgrade the motor.
wturber
1 MW
I'm not 100% sure, but I think most motors can run at higher voltages. You may not need to upgrade the motor. But what you need to do for sure is upgrade the controller and related electronics - or use a buck converter.
A typical motor controller is actually a buck converter. If you limit the throttle, the motor can be kept below 24v with a 52v battery.
The real limitation on most motors is the heat, so as long as you have the right current limit set on the controller, a 24v motor will work fine. In some cases I've see motors that try to go so fast the rotor flies apart, but that won't happen with a hub motor. The old Kollmorgen inrunner motors were rated for 24v and would fly apart somewhere around 60v. Guys ran them at 48v with good results.
The real limitation on most motors is the heat, so as long as you have the right current limit set on the controller, a 24v motor will work fine. In some cases I've see motors that try to go so fast the rotor flies apart, but that won't happen with a hub motor. The old Kollmorgen inrunner motors were rated for 24v and would fly apart somewhere around 60v. Guys ran them at 48v with good results.
Stu Summer
100 W
Fechter, that is extremely helpfu! I will try the 36V batteries I have first, be light on the throttle, see how it goes. Worst thing that could happen is I need to buy a higher power external controller.
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