Digital adjustable small power supply for car and home

[jancelot]

I need a power supply to offer regulated voltage output, in the range 3V/12V to use in the car or house. The input would be 5 volts from smartphone wall chargers or 12 volts from car cigarette lighter. It should have a knob and digital display to increase/decrease voltage in steps of 0.1 volts say. Amperage is not needed very high because it's intended to charge several smartphones, lamps, cordless drills, and general electronics.

This is because 5 or 12 volts for inputs are easy to get, but I need several voltages for different devices: 3.7v, 5v,  5.7v, 9v, etc. Of course, I can use each device's own charger, but heck, I need to carry a dozen of them for both car and wall. It's a pain in the ass.



I've tried already to buy commercial power supplies, but low voltage ones don't offer the exact voltage I need and the laptop chargers don't offer low voltages, usually only 12 to 24 volts.

Do you know of any commercial available power supply that may offer similar functionality?

[jeroen79]

Do you want to DIY? What is your skill level?

A cheap and simple solution is to get a Chinese buck/boost converter, panelmeter, binding posts and 10 turn potentiometer and put them in a box.

[Audioguru]

AC to DC power supplies with various output voltages are available but cause damage because frequently the wrong output voltage is selected.
Please learn the English word, "REGULATED".

[jancelot]

AC to DC power supplies with various output voltages are available but cause damage because frequently the wrong output voltage is selected.

Ok I think I'll be able to handle that, but the problem is if the regulated power supply generates transient spikes at the moment of connecting/slightly changing voltage, what about that?

[bitseeker]

Ok I think I'll be able to handle that, but the problem is if the regulated power supply generates transient spikes at the moment of connecting/slightly changing voltage, what about that?

Then it's a pretty poor power supply that you probably don't want to continue using. If you must use it, you could try adding a capacitor to the output to suppress transients. It'll have to be large enough for the anomalies that are generated, but not so large as to cause other potential problems. Unless you consider experiments of this nature as part of the project, you'd be better off replacing it with a better quality power supply.

[jancelot]

Ok I think I'm looking for something too much professional, which will take me a lot of time to develop and I don't have, so will search for something commercial similar to what I need.


This is the laptop car & wall charger that I have:
100w Multifunctional laptop AC DC power adapter car charger for laptop/Mobile Phone/Notebook with USB Power supply 15connector
It has fixed output voltages of 12V/15V/16V/18V/19V/20V/22V/24V. Also has an additional USB 5V female output.
For input allows 12VDC from car and 110-240VAC from wall.
Has a lot of different adapters for several laptops, but testes with my Sony and doesn't connect as good as the original charger, if you move it slightly will disconnect randomly.
It's good that also offers the same 12V output when connecting to the car, other chargers start at 15v.






Another car buck converters are the PowerStream PST-DC292 and PST-DC284. Also called RSS-PM-PST-DC292. Allows an input range of 6VDC to 33VDC and fixed output values of 1.5V, 3V, 4.5V, 6V, 7.5V, 9V, 12V. Non-isolated, common ground, spikes on the positive side are eliminated. Additional accessories are sold separately.
A similar one: http://www.maplin.co.uk/p/12v-3a-universal-dc-power-supply-with-6-power-tips-a92jh



Set of 48 connectors for laptops


Another possibility is this:
DC-DC Step Down Power Supply Adjustable Module With LCD Display With Housing Case
It's great because is quite small and comes already assembled and with a case.
It has up/down buttons so there are increases/decreases of 60mV.
The only downside is that is buck (step down) converter only, so the maximum output voltage is about 1.1v less than input, so for a car that has 12v it would be 10.9v.

[bitseeker]

Car voltage is around 13-13.8V at rest. With the engine running (i.e., alternator operating), it's 14+. So, the buck converter should be fine unless you plan to operate from the car battery for a long time with the engine off. Of course, running down your car battery has other negative effects.

[jancelot]

Ok I think I'll be able to handle that, but the problem is if the regulated power supply generates transient spikes at the moment of connecting/slightly changing voltage, what about that?

Then it's a pretty poor power supply that you probably don't want to continue using. If you must use it, you could try adding a capacitor to the output to suppress transients. It'll have to be large enough for the anomalies that are generated, but not so large as to cause other potential problems. Unless you consider experiments of this nature as part of the project, you'd be better off replacing it with a better quality power supply.

I've noticed that the spikes happen when using a power supply with discrete values and a switch to select the desired one among them. It generates spikes when changing from one selection to another, like the first two on the Reply #6. For example, when changing from 19v->20v generates a transient spike of 26.91v. I've asked the supplier and they recommend to disconnect the load before moving the selector of the output voltage.

[bitseeker]

Yes, they'll recommend that because its design is such that it can't change voltage safely. Before using it, I would verify that it doesn't spike at turn-on, too. This may not be a fair comparison, but a properly designed lab power supply can be switched on at full output voltage without a significant overshoot, if any at all.

Of course, it all depends on the what the load can tolerate. The overshoot may or may not be an issue.

[jancelot]

Car voltage is around 13-13.8V at rest. With the engine running (i.e., alternator operating), it's 14+. So, the buck converter should be fine unless you plan to operate from the car battery for a long time with the engine off. Of course, running down your car battery has other negative effects.

My car with the engine running has a voltage of 14.8v (because of the alternator) as read by the OBD2 sensor. While powered off, the voltage is 12.6v with small load, like sidelights on.

[Codebird]

My car with the engine running has a voltage of 14.8v (because of the alternator) as read by the OBD2 sensor. While powered off, the voltage is 12.6v with small load, like sidelights on.

Can power can be pretty nasty - it'll drop to under 10V when turning the starter, and can experience surges when load is suddenly reduced as the alternator regulator takes a moment to compensate.

Make sure your supply can handle at least 25V input, to give yourself some margin.

[jancelot]

Can power can be pretty nasty - it'll drop to under 10V when turning the starter, and can experience surges when load is suddenly reduced as the alternator regulator takes a moment to compensate.

Make sure your supply can handle at least 25V input, to give yourself some margin.

Vans and trucks use 24v batteries, so I guess the surges can be even higher.

[jancelot]

Here are two examples of mini adjustable power supplies at instructables:

* Mini adjustable power supply (first model by newtonn2). Video link here.

* DIY Small Bench Power Supply (newer with more accurate control of the voltage and current). Video link here.