UPS fan hacking (run only on battery power) - Page 1
Forum section: electronics / projects

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: September 27, 2017, 08:07:17 am
content: So I bought a new UPS and I'm really annoyed that the fan to cool the heat-sink for the mosfets runs continuously and is quite loud.I would like to hack the fan so that It turn on only when the power goes out as the mosfets run cool when there is AC power and only get hot when the power goes out.I don't want to just add a resistor in series to reduce the rpm of the fan as I want to keep the full cooling power when it switches to battery backup.Is there a simple way to do this?In case it helps the UPS is an Eaton 5E 1500iUSB.

author: BradC
author_rank: Super Contributor
timestamp: September 27, 2017, 08:13:01 am
content: You do need to be careful here as you'll find the device also generates significant heat when charging the battery.I can't help on a simple way to do what you want, but is there an indicator on the panel or something that changes state when on battery you could use? Does the UPS have an old switched output somewhere that toggles when on battery or is it a USB only interface?My relatively old APC SmartUPS 2200 has a fan that ran when charging, on battery and if the internal temp exceeded about 60C. I did the reverse and put a resistor across the MOSFET switch to make sure the fan always runs at a reduced speed, switching to full speed when it would normally run.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 27, 2017, 08:13:17 am
content: Your UPS is line interactive, the electronics are always enabled to regulate the voltage.Replace the fan for a more silent one, or get a UPS with bypass topology.The battery charger/tester will always generate some heat.

author: Bratster
author_rank: Frequent Contributor
timestamp: September 27, 2017, 08:15:07 am
content: Does the fan run at two different speeds? One for UPS on battery and one when it's just idling along.I have an APC 2200 XL that has two fans that run 24/7. They go to a low speed when it's just sitting there so I made a little circuit with a microcontroller on it that disconnects the fans when it's running at a low speed and reconnects them when it goes to a high-speed.If the fans are just voltage-controlled that's easy enough to do if they are pwm controlled that's a little more difficult.I also added a thermistor to my little board cuz if it does get hot in the chassis I do want the fans to come on. Now I just need to get the temperature setting correct.Sent from my Nexus 6 using Tapatalk

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: September 27, 2017, 08:30:24 am
content: Quote from: Jeroen3 on September 27, 2017, 08:13:17 amI will try a more quiet fan thanks.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: September 27, 2017, 08:33:36 am
content: Quote from: BradC on September 27, 2017, 08:13:01 amI've had many UPS of similar power and they didn't have any fans so I doubt that it is needed for charging the batteries.The UPS has only a USB interface.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 27, 2017, 10:56:05 am
content: You've probably owned bypass types. These have a relay to bypass the inverter and the only thing permanently active in those is the detection circuitry. Which will be a few watts.When used on battery they become hot quickly, but they never last longer than 30 minutes. After that charger is activated, but that is more efficient than the inverter.This is why you do not upgrade the batteries of a UPS to laster a lot longer. It might overheat.But, you now have a line interactive one. Which regulates voltage. If it does this solid state, it will need the fan.There is a topic of a teardown of a line interactive UPS from eaton. They will be similar.https://www.eevblog.com/forum/reviews/teardown-eaton-powerware-5115-1000va-usb-230v/

author: xani
author_rank: Frequent Contributor
timestamp: September 27, 2017, 05:13:24 pm
content: Try to use temperature sensor instead.There can be many other cases where fan is needed and device is powered from AC, like others mentioned charging will heat it up, or just a very hot day.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: September 27, 2017, 08:48:08 pm
content: So I've decided to test the fan under different voltages to see which one gave me an acceptable noise level (same as my PC's fans) and that turned out to be 8V so I did some math and placed a 100 Ohm resistor in series and now it cannot be heard over my computer which is perfect.Not sure how the thermals will be affected but since it will mostly be running on AC power I am not too worried about that.