Can't power multiple boost converters in parallel... Why?

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
Hey fellaz,

I currently purchased a few CC / CV Step Up boost converters in order to charge 40 volt battery packs. I took all three of them, spaced them out evenly and powered them all in parallel. If I use one at a time they work fine.

But as soon as I try to use 2 or more at the same time, they all stop "working"... The output voltages falls and current output drops to zero... And sometimes some of them will start buzzing a tiny bit.

At first I though maybe the power supply I was using didn't have enough current output but that's not the case. The power supply is rated at 10 amps and I have each boost converter current set to 1 amp or less the same problem persist.

Any ideas?

received_2270709566555654.jpegreceived_2270709566555654.jpeg
Description:
Module properties: non-isolated step-up module (BOOST)
Input voltage: DC10V-40V
Input current: 6A (MAX) exceeds4A please enhance heat dissipation
Quiescent current: 10mA (12V liter 20V, the output voltage, the higher
the current will increase too quiet)
Output voltage: 10-50V continuously adjustable
Constant] range: 0.2-6A
Temperature: -40 to + 85 degrees (ambient temperature is too high, please enhance heat dissipation)
Operating frequency: 150KHz
Conversion efficiency: up to 96%
Overcurrent protection: There
Input reverse polarity protection: Yes,
Installation: 4 3mm screw holes
Connection method: Connection Output
Module size: Length 70mm width 36mm height 13mm
Single module: 50g
 

ericgibbs

Joined Jan 29, 2010
10,820
hi b,
What is the specification of the DC power supply you are using to drive these modules, when they are loaded.?
It could be the intial inrush current to the modules [even when they are not loaded] which is causing the DC PSU to go into current limit.
Try adding one module at a time to the PSU.
E
You could try adding a high value capacitor directly on the DC PSU output and add a switch between that cap and the modules, say 1000uF or so.
 

Delta prime

Joined Nov 15, 2019
505
Hello everyone, looks like you just made one big multi-output non-isolated
PSU well... almost. Apsoluty specifications of power driving the modules.perhaps isolation between outputs, not tiying them to a common ground? Need more data please. I wonder if you use a isolated
PSU then you would have a isolated, multi-output,
non-isolated modules,with isolated outputs???
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
Do you mean when you parallel the outputs together they stop working?
If so this is probably because they mess up each others regulation control.
no not the outputs. When parallel the inputs/line side, so I can run all 3 from one power supply.

---

So I'm assuming its because not have isolated grounds going to each boost converter? So basically I would have to use three separate power supplies correct? That's kind of a pain in the a**..... is there a way to use one power supply and isolate the grounds from each other? either a bought solution or a DIY solution?

I am a DIY'er and I'm doing this for personal projects would much rather not lay out more money to buy extra power supplies if there's a way around it. I also had the same issue with a few other things where I needed the grounds to be isolated so if there is a DIY solution to isolate the grounds would be beneficial in more projects than just this one
 

Dodgydave

Joined Jun 22, 2012
9,460
Are the psu loaded, (ie.. with a load on them drawing current) , otherwise they will just run free and cause buzzing or interference...
 

MrAl

Joined Jun 17, 2014
7,813
Hello,

You did not specify what your input power supply voltage was set to.
You seem to be using a boost with 40v output, but what is the input voltage?
Is it 12v perhaps?

I assume that you are charging three batteries and the three may have a common ground. The common ground should be ok as long as the boost converters all have ground common input to output as well.

Now about the input voltage. If you have 12v input and 40v at 1 amp output then the average input current will be around 4 amps, and that means a peak of 5.33 amps for each boost converter. That means the peak current could be taking the power supply into current limit or that the power supply just can not handle the peak current of two boost converters at the same time.
Now if you intend to power two such units maybe a low ESR cap on the input of each converter might help, but powering three such converters probably wont work if you really do have 12v input. You would need higher voltage input if the current limit on the power supply really is 10 amps.

The buzzing could be because sometimes the input duty cycles overlap and sometimes they dont so the output current of the power supply is varying a lot.

So you need to specify the input supply voltage, and if possible the efficiency of the converters you are using. If the input voltage being used is too low it wont work with three converters, but maybe with just two.
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
Psu / Input voltage = 16v

Psu / input current rating = 6a

Boost Converters efficiency = 96%

and I am using the Boost converters to boost the voltage from 16v upto 40v at 1.5a

and when the Boost converters make that buzzing noise they do not output any thing. And sometimes they don't output anything and they don't buzz.

And I can only use one boost converter at a time if I try to connect 2 or more I get this problem.

I also posted the specifications of the Boost converters at the end of my original post
 

crutschow

Joined Mar 14, 2008
25,441
Did you measure the input voltage to see if it changes when you connect more than one converter?

Do you have an oscilloscope to observe the voltages?
 

MrAl

Joined Jun 17, 2014
7,813
Psu / Input voltage = 16v

Psu / input current rating = 6a

Boost Converters efficiency = 96%

and I am using the Boost converters to boost the voltage from 16v upto 40v at 1.5a

and when the Boost converters make that buzzing noise they do not output any thing. And sometimes they don't output anything and they don't buzz.

And I can only use one boost converter at a time if I try to connect 2 or more I get this problem.

I also posted the specifications of the Boost converters at the end of my original post
Hi again,

Ok then the average input power is 62.5 watts for each converter.
The power supply at 16 volts can do a total of 160 watts at 10 amps.
Two converters take 125 watts but three converters take 187.5 watts so three will never run ok unless the output current is less than what you specify as 1.5 amps.
If each converter only took about 53 watts then they MIGHT run ok but that is subject to testing. That would mean only about 3.2 amps input each converter, which means about 1.3 amps out each converter max.

But then there is that peak current issue again. The peak input current will be around 5.33 amps with those operating conditions above, so that means 16 amps peak when duty cycles overlap (and they will always overlap for some time at least 20 percent of the time for just two converters). That means you need good caps on the input of each converter. Maybe they have enough already maybe they dont. So this is subject to testing. If the tests fail (even at the lower output current above of 1.3 amps) then you need low ESR caps on the input of each converter and short wiring.

One thing is certain though, three converters at 1.5 amps out each and 40 volts out each with just 160 watts input will never run because the needed output power is greater than the available input power. At 96 percent efficiency the total required input power is almost 190 watts and the available input power is only 160 watts.
That and 96 percent is pretty high it may only be 90 percent realistically which would require 200 watts input power.

I can see this working at maybe 1 amp output though for each converter as long as the input caps are low ESR. However, we did not yet consider input power surges when the converters are all just turned on after being off for a while. If the surges cause the power supply to go into foldback regulation all is lost unless maybe one converter is turned on at a time. That may not work either though depending on the surge amplitudes.
 
Last edited:

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
@MrAl - wow thank you so much for your detailed explanation. Now I actually understand exactly what the problem is. I wish there was more people like you. Lol. But I also can understand how some people will put a lot of time into answering a question for the original poster not to give a sh*t or not read it and keep asking same questions... Thank you again!

@BobTPH - yup. Ita makes asencea nowa... LOL

Glad to hear that the problem is just not having enough input power to power all three or even two of them at the same time. And it's not being caused by not having isolated supplies / grounds for each one..

I had just assumed that if there wasn't enough input power that one of them would at least still work and not the other two or whatever but now that I think about it, it makes sense... I'm sure I have a couple of cheap 12v, 18v etc power supplies laying around that I can use for the next day or two until my new ac-dc converter (power supply module) comes in. 48v 12a.

In a few minutes I'm going to power up the boost converters and set them each to maybe 30v @ 0.5a and then can connect one at a time and monitor input voltage and see if I can connect two or all three together without having this same issue. That will tell me a hundred percent if that is the issue.

I'm a residential electrician for 20 + years and I have to deal with wires all day as you can imagine so when I'm home doing my DIY electronic projects the last thing I want is all sorts of unnecessary wires and power bricks LMFAO. I really hope just getting a bigger supply will take care of this issue instead of having to use three separate power supplies.

I'll do the test here shortly and post my results
 

BobTPH

Joined Jun 5, 2013
2,541
In a few minutes I'm going to power up the boost converters and set them each to maybe 30v @ 0.5a and then can connect one at a time and monitor input volta
Careful with that. You need to have a load that draws 1A at 30V to do that test. Just setting you boost converters without the appropriate load will not tell you anything.

Also, when you are boosting, the input power s only on for part of the the time, and so the peak current it draws is more than the average current that you calculate based on power alone.
 

MrAl

Joined Jun 17, 2014
7,813
@MrAl - wow thank you so much for your detailed explanation. Now I actually understand exactly what the problem is. I wish there was more people like you. Lol. But I also can understand how some people will put a lot of time into answering a question for the original poster not to give a sh*t or not read it and keep asking same questions... Thank you again!

@BobTPH - yup. Ita makes asencea nowa... LOL

Glad to hear that the problem is just not having enough input power to power all three or even two of them at the same time. And it's not being caused by not having isolated supplies / grounds for each one..

I had just assumed that if there wasn't enough input power that one of them would at least still work and not the other two or whatever but now that I think about it, it makes sense... I'm sure I have a couple of cheap 12v, 18v etc power supplies laying around that I can use for the next day or two until my new ac-dc converter (power supply module) comes in. 48v 12a.

In a few minutes I'm going to power up the boost converters and set them each to maybe 30v @ 0.5a and then can connect one at a time and monitor input voltage and see if I can connect two or all three together without having this same issue. That will tell me a hundred percent if that is the issue.

I'm a residential electrician for 20 + years and I have to deal with wires all day as you can imagine so when I'm home doing my DIY electronic projects the last thing I want is all sorts of unnecessary wires and power bricks LMFAO. I really hope just getting a bigger supply will take care of this issue instead of having to use three separate power supplies.

I'll do the test here shortly and post my results
Hi,

You are welcome and thank you too.

It will be very interesting to see what you can get to work with the tests you intend to perform. See if you can get something working at lower currents. I am very interested to hear what results you get.
 
Top