Could really use help on simple DC power supply - Page 1
Forum section: electronics / projects

author: viper
author_rank: Regular Contributor
timestamp: January 07, 2025, 10:23:50 pm
content: Rather than just plugging in requirements, I will give you guys the back story as maybe some EEs will have a simple idea for me.I am working with an RV furnace blower. These furnaces run on nominal 12VDC. The problem is because the voltage is variable going to the furnace, the blower speed changes! When running strictly on battery power, voltage would be around 12.4-12.6V, depending on battery SOC. However, when on solar or AC charger, obviously we are at a "charging voltage" of around 14-14.8VDC.What I have realized is due to the poor furnace ducting design, it will constantly trip the high thermal limit switch when on battery power. When on charge voltage, the blower is pushing harder, which totally solves the problem!The load current is about 10A, max. So I am trying to figure out a DC/DC converter that would give me a constant, and ideally adjustable output, from the variable DC input of about 11.8-14.8VDC input.I don't know if a typical boost converter can buck? There may be times when actual charge voltage is at 15V, and the furnace has taken it, but just asking the question. I'd probably settle for a voltage that makes the furnace blower happy and no more.

author: moffy
author_rank: Super Contributor
timestamp: January 07, 2025, 11:09:22 pm
content: You need either a SEPIC converter or a BUCK BOOST power supply, found some BUCK BOOST on Aliexpress but the output isn't adjustable.https://www.aliexpress.com/item/1005004580664992.html?spm=a2g0o.productlist.main.35.68fe22b6iEKzjp&algo_pvid=af11340d-999b-443a-b5bb-ebab529f55be&algo_exp_id=af11340d-999b-443a-b5bb-ebab529f55be-17&pdp_npi=4%40dis%21AUD%2127.59%2127.59%21%21%2116.99%2116.99%21%402101e9a217362910467232290e355f%2112000029705703889%21sea%21AU%213509633182%21X&curPageLogUid=iADOveCcwx48&utparam-url=scene%3Asearch%7Cquery_from%3A

author: moffy
author_rank: Super Contributor
timestamp: January 08, 2025, 06:55:57 am
content: Or you could purchase/build a simple boost converter to boost to 15V then use a simple PWM output to control the motor speed, I am assuming it is a simple DC motor which would filter the PWM output.

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2025, 12:14:58 pm
content: A boost converter can't buck, but there's no need for that, since you don't a need step-down, as the furnace has worked with 15V with no problem.A boost converter will work, as long as all of the components are rated to the maximum possible input voltlage. Set the output voltage to 14V, or whatever is required to maintain the required blower speed. If the input voltage exceeds that, by a diode drop, then the controller will reduce the switching duty cycle to zero and the output will simply be a diode drop less than the input.

author: viper
author_rank: Regular Contributor
timestamp: January 08, 2025, 02:12:05 pm
content: Thanks guys! One potential issue I thought of is there is a mounted controller board inside the furnace that controls some delays, electric starter, etc. My intent, due to being insane easier, is to boost the leg that goes to the entire furnace, which would be the controller board and blower. However, I am wondering if that board will be happy with the 'PWM?' output of a boost controller? Or are they usually high enough frequency that DC gear usually doesn't care?If I have to go into the furnace to do the mod, it's nearly impossible to get to. Can't wait for the day it fails...lol It will be dramatic.

author: moffy
author_rank: Super Contributor
timestamp: January 08, 2025, 02:18:37 pm
content: The controller board will prefer a DC input, no predicting what a noisy PWM signal would do to the controller.

author: viper
author_rank: Regular Contributor
timestamp: January 08, 2025, 03:29:01 pm
content: Sort of thinking out load but what would a parallel electrolytic capacitor do for that noisy output?

author: Zero999
author_rank: Super Contributor
timestamp: January 08, 2025, 04:43:42 pm
content: Quote from: moffy on January 08, 2025, 02:18:37 pmA boost converter will have a DC output, not PWM. There might be some noise, but the controller should be able to cope with it, as long as it's not too bad.