I've built a battery powered guitar amplifier using the 12v amp stage from a 1960's portable transistor radio. I powering the amp using a power bank and an adjustable usb DC-DC buck booster set to put out 12v.
It works when I use one power bank - PowerAdd 15000mah - it has two 2.4a outputs.
Unfortunately, the PowerAdd is too big to fit inside the amp enclosure, and I want to use another one I have knocking around - a Cygnett 5000mah - which has two outputs it claims are also 2.4a each. When I plug the buck booster in its LED readout reads 18v but when I engage the amp circuit the booster makes a clicking noise and its LED readout shows an error.
If I set the buck booster to 9v and plug in the amp, it works and then, strangely, if I adjust the voltage on the booster I can get it up to 18v with no error.
I'm fairly certain that the load of the amp is too great - or the immediate appearance of the load is too great - and the Cygnett cannot put out enough current and switches itself off. Is there some way I can get the Cygnett to play nicely with the buck booster? Some sort of buffer in between? Or just find another power bank?
It works when I use one power bank - PowerAdd 15000mah - it has two 2.4a outputs.
Unfortunately, the PowerAdd is too big to fit inside the amp enclosure, and I want to use another one I have knocking around - a Cygnett 5000mah - which has two outputs it claims are also 2.4a each. When I plug the buck booster in its LED readout reads 18v but when I engage the amp circuit the booster makes a clicking noise and its LED readout shows an error.
If I set the buck booster to 9v and plug in the amp, it works and then, strangely, if I adjust the voltage on the booster I can get it up to 18v with no error.
I'm fairly certain that the load of the amp is too great - or the immediate appearance of the load is too great - and the Cygnett cannot put out enough current and switches itself off. Is there some way I can get the Cygnett to play nicely with the buck booster? Some sort of buffer in between? Or just find another power bank?
Your report indicates that it is the switch-on load that is too high for the smaller powerbank. Most amps have a (much) higher current consumption at switch-on with all the capacitors and whatnot needing to be charged up.
Apparently the small powerbank cannot handle the start-up surge but it can handle the continuous draw. What you did by switching on at a lower voltage and then turning it up is giving it a slow start.
Unless you can use this 'slow start' you probably need to find a powerbank that can handle the inrush.
Jan
Apparently the small powerbank cannot handle the start-up surge but it can handle the continuous draw. What you did by switching on at a lower voltage and then turning it up is giving it a slow start.
Unless you can use this 'slow start' you probably need to find a powerbank that can handle the inrush.
Jan
How old is the Cygnett?
PS: All these power banks will have some form of current protection.... to prevent you from turning them into an incendiary device.
PS: All these power banks will have some form of current protection.... to prevent you from turning them into an incendiary device.
Thanks, Jan. That sounds about right. Is there an electronic component I can add in between the buck booster and the amp that will soften the bump...some sort of capacitor? (I'm quite new to electronics)
It was gifted to me by a friend so I'm not sure. Not more than 3 years old I'd guess.
Find another power bank that will physically fit
It's more than likely it's the overcurrent protection kicking in, unless the cells are in bad shape.
It'll be awkward. You can add a small resistor of say 5 ohms in series with the power line, then switch on the amp, then short out the resistor. Not user friendly. You'd probably want to find a slightly more powerful powerbank.
Would be nice if you could just try some out; my gut feeling is that a modern, about 8Ah one would do and might be small enough for you.
If you could make the boost/buck make come on slowly, like in a second or so, that would most probably also work, but I don't know if that is at all possible with what you have.
Jan
I wonder if there's some sort of on/off potentiometer that I can feed the 18v into and outputs 0v to 18v across its range...?
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You're of course describing what is in many large transformered products, an inrush current limiting control system.
You can automate the procedure (just like the products described) by adding a 555 timer to short the resistor out via a relay - or a separate RC circuit, so every power up the resistor is in-line, and the 555 is started (or the RC cap charging is started) , after a preset time, the relay kicks in and stays on for the duration of use.
You might have to jiggle the values to suit the load., you could even stage a couple of relays with different value resistors to ramp it up in stages.
messing about a bit , cos the ideal way is just buy a different power pack
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How many watts is the amp?
How long does it need to play?
That will tell you battery capacity.
Start from there.
How long does it need to play?
That will tell you battery capacity.
Start from there.
That is a bit of a complicated fix for me and a buying a different power bank is probably the best solution. However, searching inrush current limiting has led me to NTC Thermistors, could one of those work? They provide the resistance described but once they heat up everything passes through. I've found some calculators online but I'm afraid the various parameters they ask to input are way beyond me.
I had a similar issue powering a motor from a laptop power brick.
The motor drew around 400mA. The power brick was rated at 3.5A.
At start up the motor DC resistance suggested an instantaneous 10A was possible so the brick shut down.
The solution was a CC/CV regulator board. The Constant Current function acted as current limiter, set at 3A it didn't slow the motor start up speed in any discernible way but prevented the power brick shut down.
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=202605338573&_sacat=0
If you set the voltage regulation higher than the output of your buck convertor then it will pass the full voltage and only limit the current.
The motor drew around 400mA. The power brick was rated at 3.5A.
At start up the motor DC resistance suggested an instantaneous 10A was possible so the brick shut down.
The solution was a CC/CV regulator board. The Constant Current function acted as current limiter, set at 3A it didn't slow the motor start up speed in any discernible way but prevented the power brick shut down.
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=202605338573&_sacat=0
If you set the voltage regulation higher than the output of your buck convertor then it will pass the full voltage and only limit the current.
Without more specs and doing some checks with a acope etc, you're gonna have to experiment with different thermistors.
Ideally you'd still have the relay to completely take the thermistor out of crcuit once you're out of the startup/inrush phase... but if not you need to choose a thermistoer that's capable of thre steady state current (which isn't really steady state on this product anyway , so just go for a max.)
I'd suggest start with a 5R, 10R or 22R (at room temp) to start with at an appropriate current rating.
Be aware they will/can get hot in normal operation, depending on the circuit they're feeding
Well, this sounds like the perfect fix. (I'm really invested in the Cygnett power bank because, not only does it fit perfectly in the enclosure I've also hacked its on/off switch so that it's controlled by another switch)
I only need one so I might get this one which ships from the UK. Is it effectively the same thing?
So, I'd adjust the output voltage to stay the same, adjust the max current output to be 2.4a (same as the stated power bank output), but what does the third trimpot adjust?
My only worry is that is might create EMI that will affect the amp. My current buck booster is silent but I had one from aliexpress that created a terrific squeal - tried shielding it, hot gluing the inductor but is wouldn't shut up. I guess the CC CV is cheap enough to experiment.
Thanks. I suspect - and I think you might have been alluding to this - that the amp's fluctuating draw of voltage/current will not give the thermistor a stable enough flow to remove itself from the circuit and it will constantly be cooling off/heating up and will probably have an affect on the sound.
Adjust voltage (CV) to max - screw pot as far as it will go, it will not limit voltage.
Adjust current CC to 2.4A as you said. Just connect a DMM on 10A range across the output to set. CC means it will pass the adjusted current into a dead short. It won't fry.
The centre pot, 'full turn lamps, current regulation', ignore. It's trickle current adjustment if using the board as a battery charger. Even the suppliers say not to adjust (when they give any instructions at all).
I bought a CC CV module but no luck, I'm afraid.
I tried it positioned POWER BANK>CC CV>BUCK BOOST>AMP - when the amp was engaged the power bank stayed awake BUT when I played guitar through the amp the volume fluctuated rapidly like a tremolo effect. I think the amp was drawing more power and caused the current limiter to kick in. The voltage on the buck booster also fluctuated. When the guitar strings stopped ringing everything went back to normal but any playing of the guitar caused it to happen again. Tried adjusting up the CC trimpot but it kept happening.
I tried it positioned POWER BANK>BUCK BOOST>CC CV>AMP - the power bank went to sleep even before the amp was engaged, seemingly the CC CV caused it. Tried adjusting the CC up and down but it didn't help. Also the CC CV made some audible squealing when I tested it with the multimeter.
I'm going to try swapping the PCB multi-turn trimpot that adjusts the voltage on the buck booster for a single turn potentiometer installed on the enclosure and dial it up as part of the switching on process. All I need to do is figure out how to make the new pot stop at 18v without being able to see the buck booster LED read-out hidden inside the enclosure.
I tried it positioned POWER BANK>CC CV>BUCK BOOST>AMP - when the amp was engaged the power bank stayed awake BUT when I played guitar through the amp the volume fluctuated rapidly like a tremolo effect. I think the amp was drawing more power and caused the current limiter to kick in. The voltage on the buck booster also fluctuated. When the guitar strings stopped ringing everything went back to normal but any playing of the guitar caused it to happen again. Tried adjusting up the CC trimpot but it kept happening.
I tried it positioned POWER BANK>BUCK BOOST>CC CV>AMP - the power bank went to sleep even before the amp was engaged, seemingly the CC CV caused it. Tried adjusting the CC up and down but it didn't help. Also the CC CV made some audible squealing when I tested it with the multimeter.
I'm going to try swapping the PCB multi-turn trimpot that adjusts the voltage on the buck booster for a single turn potentiometer installed on the enclosure and dial it up as part of the switching on process. All I need to do is figure out how to make the new pot stop at 18v without being able to see the buck booster LED read-out hidden inside the enclosure.
You do realise that stepping up the voltage reduces the available current pro-rata?
2.4A @ 5V = 0.6A @ 18V (assuming close to 100% efficiency).
Reduce the boost voltage until it works.
POWER BANK>CC CV>BUCK BOOST>AMP is the one I'd go for.
2.4A @ 5V = 0.6A @ 18V (assuming close to 100% efficiency).
Reduce the boost voltage until it works.
POWER BANK>CC CV>BUCK BOOST>AMP is the one I'd go for.
First I hooked it up after the buck booster (set to 18v) and I put the probes of the DMM (set to 10a) across the +ve and -ve outputs.
Then I hooked it between the booster and the power bank and got the fluctuating sound coming out of the amp. I keep playing guitar and kept turning the screw down on the trimpot but the fluctuation remained.
I'll try it again and see what happens.