Hi. I am a software engineer retired. I know a small amount in electronics.
I saw couple of threads on how to setup the amps with the screw adjustment on a 400w 15 amp buck boost converter, mainly this one
https://forum.allaboutcircuits.com/...c-step-up-boost-converter-10-60-volts.192456/

I have this DC-DC Converter 15A 400W Step Up Buck Boost converter from Aliexpress .
https://www.aliexpress.com/item/1005010299199456.html?spm=a2g0o.productlist.main.1.7b109PpA9PpAAT&algo_pvid=f5b06b3a-ec10-4a8d-b23e-473455bbec12&pdp_ext_f={"order":"14","eval":"1","fromPage":"search"}&utparam-url=scene:search|query_from:|x_object_id:1005010299199456|_p_origin_prod:

I am not able to adjust the current like many other posts. i understand partly that there is a ratio between the input amp and voltage and the output.

I have a small bench power 30v 10amps providing 12.2v same as battery to the converter with output of 24v 2.75 amp max,.
At 35 watts I think only 2 amps should be needed.
I will need about 35 watts for a CPAP machine max with humidifier and heat for the tubing turned off.
I have seen another post where he was using a led. I am using a CPAP machine. The problem I am having is that when it turns on, it draws a minimal current. But when i turn the CPAP machine on to push air, it draws enought current that I assume the converter is not providing and it dies in less the 2 seconds, so I don;t have time to adjust.
Should i do the same as turning the screw back 30 turns to put it to 0 on the converter and put max voltage on my bench and zero amps on it. Then turn the cpap on then put amp meter between cpap and converter and regulate the amps? My problem is this is not taking the current immediatly, and if it starts and starves, it turns off.
My idea was to adjust the converter with a dummy load that would take 24v and adjust to 2 amps then plugin cpap and then adjust.

I am trying to use this to have a backup battery for my CPAP. I could just buy the $60 adapter but bought 2 of those converter to try and do this project.
I have a Resmed Airsense 10 and 11.
I have done most of the work as the CPAP takes 24v another line at 3.3 and then you apply a 2700k resistor to the 3.3v line.
Any help would be appreciated.
Thx

 

Your CPAP machine is almost certainly designed to run on a fixed voltage, not current. Setting a current on the converter means the voltage will vary to get exactly that current. That is not what you want.

You need to supply it with the correct voltage from a supply that is capable of providing the max current it needs plus s 25-50% margin for reliability and longevity.

What does the original power supply say? They usually state the voltage and max current.

 

You cannot adjust both operating current I and voltage V at the same time on a power supply unit (PSU).
The current will be determined by the applied load R, given by Ohm's Law:

I = V / R

Current and voltage settings are limits, i.e. the maximum allowed. The PSU will automatically reach one of the two limits, either current limit or voltage limit.

For a voltage supply, set the current to the maximum (or maximum current expected).
Then set the voltage for the required voltage.

 

A boost converter should provide a regulated output voltage regardless of load current. Adjust it for 24 volts at no load and it should provide very close to the same voltage when loaded.

If not, you may be drawing more current than the power supply (or battery) can provide.

I am running my CPAP (which requires 12 volts) from a USB-C PD supply to eliminate the bulky heavy standard power supply when charging. Unfortunately, 12 volts is no longer included in the USB-C PD specification so not all PD supplies deliver it. I am using a PD trigger set to 20 volts, and a 10 amp buck converter to get to 12 volts. It works great.

 

The TS did not ever mention either the voltage for that CPAP machine, nor the current requirement.
WITHOUT KNOWING THE REQUIREMENTS THERE IS NO WAY TO PROVIDE ANY USEFUL ADVICE! ! !

With the power supplies described, usually a power supply output is specified as a voltage range and either the maximum current or the maximum output watts.
The information we first need is the load voltage and the load current.

 

Your CPAP machine is almost certainly designed to run on a fixed voltage, not current. Setting a current on the converter means the voltage will vary to get exactly that current. That is not what you want.

You need to supply it with the correct voltage from a supply that is capable of providing the max current it needs plus s 25-50% margin for reliability and longevity.

What does the original power supply say? They usually state the voltage and max current.

It is aa 95w power supply delivers 24v 3.75 amps `from resmed

 

You cannot adjust both operating current I and voltage V at the same time on a power supply unit (PSU).
The current will be determined by the applied load R, given by Ohm's Law:

I = V / R

Current and voltage settings are limits, i.e. the maximum allowed. The PSU will automatically reach one of the two limits, either current limit or voltage limit.

For a voltage supply, set the current to the maximum (or maximum current expected).
Then set the voltage for the required voltage.

Do you mean to adjust the max voltage on the dc to dc converter? I need 24v wit around 2 amps with the settings on my machine at the moment.

 

A boost converter should provide a regulated output voltage regardless of load current. Adjust it for 24 volts at no load and it should provide very close to the same voltage when loaded.

If not, you may be drawing more current than the power supply (or battery) can provide.

I am running my CPAP (which requires 12 volts) from a USB-C PD supply to eliminate the bulky heavy standard power supply when charging. Unfortunately, 12 volts is no longer included in the USB-C PD specification so not all PD supplies deliver it. I am using a PD trigger set to 20 volts, and a 10 amp buck converter to get to 12 volts. It works great.

for the testing I am using my bench 30v 10amp power supply and feeding the buck converter. it was set at 24v 5 amp to feed and voltage on buck was 24 steady I was not able to verify amps as it ramps up and shuts down. I will be using a big lifepo4 abatt with bms. What is your cpap machine and how many amps is it drawing for hao many hours? thx

 

The TS did not ever mention either the voltage for that CPAP machine, nor the current requirement.
WITHOUT KNOWING THE REQUIREMENTS THERE IS NO WAY TO PROVIDE ANY USEFUL ADVICE! ! !

With the power supplies described, usually a power supply output is specified as a voltage range and either the maximum current or the maximum output watts.
The information we first need is the load voltage and the load current.

You are right! the airsense 10 has a power supply of 90 watts at 110v 1 - 1,5 amps and delivers 24v 3.75amps max when everything is on.
For economy sake, the thermal plate is OFF and heated tubing is OFF. When I checked for 15 minutes about it was drawing around 30 watts.

 

I need 24v wit around 2 amps with the settings on my machine at the moment.

Why do you think you need to limit current to 2A? Just set the DC-DC converter to 24V and the CPAP machine will take whatever it needs, up to the maximum current of the regulator. Though it sounds like additional heatsinking is needed for currents above 8A.

 

If your CPAP machine requires 24 V, set the power supply to 24 V.
If the machine draws 100 W, set the power supply to deliver more than 5 A.

 

Your CPAP machine is almost certainly designed to run on a fixed voltage, not current. Setting a current on the converter means the voltage will vary to get exactly that current. That is not what you want.

You need to supply it with the correct voltage from a supply that is capable of providing the max current it needs plus s 25-50% margin for reliability and longevity.

What does the original power supply say? They usually state the voltage and max current.

The buck converter was at 24v and stayed around that number when I started the cpap. Not sure when I turned the cpap pressure on bcus happens very fast 24v seems stable but it dies. Was assuming not enough current. Maybe input current was too low. I set it at 5 amps.

 

The TS did not ever mention either the voltage for that CPAP machine, nor the current requirement.
WITHOUT KNOWING THE REQUIREMENTS THERE IS NO WAY TO PROVIDE ANY USEFUL ADVICE! ! !

With the power supplies described, usually a power supply output is specified as a voltage range and either the maximum current or the maximum output watts.
The information we first need is the load voltage and the load current.

90 watts sorry but 24v 3.75 amps

 

Why do you think you need to limit current to 2A? Just set the DC-DC converter to 24V and the CPAP machine will take whatever it needs, up to the maximum current of the regulator. Though it sounds like additional heatsinking is needed for currents above 8A.

I though the screw was to give a min current of not to limit. As the screw for the voltage is set to 24. I though it was to give a min of. So I should adjust the current screw at 0. I read that you give 30 turns left and it puts it to starting point or zero.

 

I though the screw was to give a min current of not to limit. As the screw for the voltage is set to 24. I though it was to give a min of. So I should adjust the current screw at 0. I read that you give 30 turns left and it puts it to starting point or zero.

No. You need to set the current to the maximum setting.

 

No. You need to set the current to the maximum setting.

Put 10 amps on power supply just in case and increased the screw about 30+- turns clockwise to increase to maximum and it worked on airsense 11 and 10 !!!! Average currentc draw is 1.8 amp but when I have a leak, goes up to 3.6 amps on the 12v side. So if i have a lot of leaks in my sleep will have over twice the consumption. Have finished tests on power supply now working on battery. Will be using a Avapow booster pack 4000 amp that is supposed to be rated around 105 ah. Would like to use this as always running and taking over if loose electricity. Will let you know on following results. At around 0.6 to 1.8 amps on the 24 volt side the heatsink are not even warm. If I don't have good results, I plan on buying a 100ah Lifepo4 with bms and bluetooth access to see usage aand setup.
https://www.amazon.ca/ECO-WORTHY-Li...B0969SSC5L/ref=pd_ci_mcx_mh_mcx_views_1_image
at 90% gives 12.6v gives 1152wh of usage. I plan also to have an inverter to run a fan as I need it at night.

 

It is aa 95w power supply delivers 24v 3.75 amps `from resmed

Then get a 24V battery and you do not need a converter, just wire it to a plug and plug it in.

 

Then get a 24V battery and you do not need a converter, just wire it to a plug and plug it in.

Absolutely !!! If you can give me the $$$ going from the 12.8 100ah to the 24V twice the capacite more then twice the price goes from $240 CAD to $569 !!! + 15% tx I'm willing to open a GoFundMe raise for my sleep lol it would give me a space for couple of days of usage in case of power outage. Like I said with my CPAP will take around 1.64amp with leak at 24 v 36w for 9 hours -+ = 324wh plus my fan at .33 amp at 120v 39.6 watts x 9h 356wh total 680wh the 24v has 2304wh at 90% capacity so I would be using about 29.5% gives me a lot of lea way! Would be nice but $654.
Last thing for a managed battery like the Eco-worthy on amazon managed my BMS and Bluetooth do you think I would be able to use it plugged in with a 20 amp intelligent charger or actually use the power supply from resmed plugged in the battery or something close. I saw on the pilot 24 battery it uses the power to charge the battery and power the cpap at the same time and when power goes out you rely on the battery. Its battery is 95wh.

 

You could replace the 12V 100 Ah + boost converter with a 40 Ah 24V battery. It will give the same run time and weigh less.

 

You could replace the 12V 100 Ah + boost converter with a 40 Ah 24V battery. It will give the same run time and weigh less.

You don't like my GoFundme solution lol I am checking for the 24v battery right now.