# USB powerbank with pure 5V output

#### new6ton

Gold Member
I guess USB powerbank have switching power supply for the 5V output? I need a pure 5V power bank that doesn't use switching power supply but just pure output like the 3.7v lithium battery in cell phone. And why doesn't lithium battery doesn't produce 5 volt dc output?

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#### davenn

Gold Member
And why doesn't lithium battery doesn't produce 5 volt dc output?
because of the chemistry

I need a pure 5V power bank that doesn't use switching power supply
use a linear regulator ... a little lossy in comparison to a switching (buck converter) regulator
but at least it smooth

So, why do you need a very smooth supply ?
maybe it doesnt need to be as smooth as you imagine ?

Dave

#### Torbert

For temporary (3 hour) low power (.06 w) output I used lithium ion (3.7v) in series with an alkaline (1.5v) battery for a five volt application. No recharging, or high power draw. I could have used a nickel hydroxide (1.2v) rechargeable but needed the full five volts. Mix and match is a very limited system for output power but can provide quite a variety of voltages.
Another project used a 13.8 volt DC power source, a full wave rectifier with a capacitor array minimizing ripples in voltage. This would output 400w of stable DC power. Inputting the proper resistance put the voltage anywhere from 0 to 13.8 volts.

Intended use makes all the difference in requirements.

#### davenn

Gold Member
For temporary (3 hour) low power (.06 w) output I used lithium ion (3.7v) in series with an alkaline (1.5v) battery for a five volt application.
I guess you have never heard of the "rule" about not mixing battery tupes ( chemistries) and voltages ?
It seriously is a bad idea

#### anorlunda

Mentor
I need a pure 5V power bank that doesn't use switching power supply but just pure output
Why is that? I'm just curious.

#### eq1

Gold Member
So, why do you need a very smooth supply ?
maybe it doesnt need to be as smooth as you imagine ?
And just as important, over what frequency range?

In 2019 it's possible to get cheap supplies that switch at many MHz with lots of closed-loop gain into the 100s of KHz.

#### new6ton

Gold Member
Why is that? I'm just curious.
It's to power a very expensive laboratory equipment, a spectrometer so I can bring it outside with a laptop. The spectrometer says 5V, 1A at the back.

Currently, It's power via Meanwell adaptor (see picture):

I want very pure 5v output so it won't ruin the circuit inside. I heard ordinary USB powerbank has switching power supply, and not good as it's pure? Pure means like output from 3.7v lithium battery like used in cellphone, without any switching noises, etc.

#### berkeman

Mentor
It's to power a very expensive laboratory equipment, a spectrometer so I can bring it outside with a laptop. The spectrometer says 5V, 1A at the back.
I want very pure 5v output so it won't ruin the noise performance of the circuit inside.

The professional EE approach to these types of applications (as suggested already in this thread by @davenn ) is to use a higher battery source voltage (like 12V) with a DC-DC buck converter to make an intermediate voltage that a linear LDO then smooths out. I've used this topology for 80dB radio modems, for example.

#### new6ton

Gold Member

The professional EE approach to these types of applications (as suggested already in this thread by @davenn ) is to use a higher battery source voltage (like 12V) with a DC-DC buck converter to make an intermediate voltage that a linear LDO then smooths out. I've used this topology for 80dB radio modems, for example.
I don't want to build anything. I just want to buy a readily available one. Any product one can suggest that outputs the most purest DC 5v ever? I don't want to build or use nontested ones because I don't want the voltage to suddenly rise to DC 10 volts or so and ruin the $16,000 spectrometer. #### berkeman Mentor I don't want to build or use nontested ones because I don't want the voltage to suddenly rise to DC 10 volts or so and ruin the$16,000 spectrometer.
So your are worried about overvoltage faults, not ripple voltage on the outputs? Lordy...

#### new6ton

Gold Member
So your are worried about overvoltage faults, not ripple voltage on the outputs? Lordy...
I'm just worried of anything that can ruin the circuit inside. I don't know what is the circuit inside but it's mostly the CCD and programmable microcontroller. Can't ripple voltage damage them?

#### berkeman

Mentor
Buy a standard power supply product. Better yet, buy the standard power supply that the vendor sells for that instrument. What in the world is the problem here?

#### new6ton

Gold Member
Buy a standard power supply product. Better yet, buy the standard power supply that the vendor sells for that instrument. What in the world is the problem here?
The standard power supply is the AC adaptor. Remember I need the battery pack to carry it outside with my laptop into wine shops to scan the purity of their wines or contaminants. The manufacturer doesn't have battery pack.

#### berkeman

Mentor
Ah, thank you. I understand better now. Can you post a picture and a link to the datasheet for the standard AC-DC power supply that the manufacturer supplies for this product? That will help us to point you to a compatible battery-powered supply.

#### new6ton

Gold Member
Ah, thank you. I understand better now. Can you post a picture and a link to the datasheet for the standard AC-DC power supply that the manufacturer supplies for this product? That will help us to point you to a compatible battery-powered supply.

I did. The AC adaptor for it is:

I asked. They don't have any battery pack and don't know how to suggest any.

#### Baluncore

Can't ripple voltage damage them?
That is a general power input. The instrument will have it's own internal supply regulation and protection. External noise +/- 0.25V, on the DC 5V supply will be unimportant.

When you are fearful of the unknown, find out what is going on. Read the specifications on the power input requirements.

Why will you not identify the make and model of the spectrometer?

#### new6ton

Gold Member
That is a general power input. The instrument will have it's own internal supply regulation and protection. External noise +/- 0.25V, on the DC 5V supply will be unimportant.

When you are fearful of the unknown, find out what is going on. Read the specifications on the power input requirements.

Why will you not identify the make and model of the spectrometer?
The model is this exactly. http://enspectr.com/portfolio/enspectr-r532/

#### berkeman

Mentor
Ah, sorry, yes you did already post this. Since it's an AC-DC converter brick, it will have ripple on its output, so that shouldn't be an issue with your battery powered solution.

I would just use a medium-size 12V battery with an off-the-shelf 12V to 5V DC-DC converter circuit. 4A is a pretty high output current, so it may take some searching to find a good converter module.

How long do you need this instrument to run off of a battery supply?

#### new6ton

Gold Member
Ah, sorry, yes you did already post this. Since it's an AC-DC converter brick, it will have ripple on its output, so that shouldn't be an issue with your battery powered solution.

I would just use a medium-size 12V battery with an off-the-shelf 12V to 5V DC-DC converter circuit. 4A is a pretty high output current, so it may take some searching to find a good converter module.

How long do you need this instrument to run off of a battery supply?
It's 1A only, the back of the spectrometer has this label:

I want to run the battery pack less than 1 hour only.

#### new6ton

Gold Member
Ah, sorry, yes you did already post this. Since it's an AC-DC converter brick, it will have ripple on its output, so that shouldn't be an issue with your battery powered solution.

I would just use a medium-size 12V battery with an off-the-shelf 12V to 5V DC-DC converter circuit. 4A is a pretty high output current, so it may take some searching to find a good converter module.
It's risky to use 12V to 5V DC-DC converter circuit. What if the converter get broken in the future. Then the entire 12V will get into the unit and ruin it. It's too risky to ship a $16,000 unit around the world. I want a battery pack that doesn't use any converter but just pure 5V but worry free. How long do you need this instrument to run off of a battery supply? See photo and answer in last message. #### berkeman Mentor So a 12V, 1Ahr battery source would give you plenty of margin. What have you found for 12V input, 5V output DC-DC converter modules? If you use a simple 12V lead acid deep-discharge battery (like I do for my HAM radio setups), you can use a simple/cheap car battery charger to recharge the battery source... #### new6ton Gold Member So a 12V, 1Ahr battery source would give you plenty of margin. What have you found for 12V input, 5V output DC-DC converter modules? If you use a simple 12V lead acid deep-discharge battery (like I do for my HAM radio setups), you can use a simple/cheap car battery charger to recharge the battery source... View attachment 251432 See my last message. It's risky to use 12V to 5V DC-DC converter circuit. What if the converter get broken in the future. Then the entire 12V will get into the unit and ruin it. It's too risky to ship a$16,000 unit around the world. I want a battery pack that doesn't use any converter but just pure 5V but worry free.

And the 12v is too bulky.

The following is another product by another company that uses the same unit but made it portable. Did you see their battery pack? It's compact and small size. What could it be?

Remember since I didn't buy these specific products. They won't tell me what kind of battery or circuit for it. Its portable unit is \$3000 more expensive.

#### rbelli1

Gold Member
Meanwell also sells switching converters meant for low voltage input that have a 5V output. If you can trust the very expensive device to the Meanwell AC power adapter you should be able to trust it to their other converters.

Meanwell DDR

BoB

#### new6ton

Gold Member
Meanwell also sells switching converters meant for low voltage input that have a 5V output. If you can trust the very expensive device to the Meanwell AC power adapter you should be able to trust it to their other converters.

Meanwell DDR

BoB
The problem is together with the 12V battery. It's bulky. I just need something like this:

Could it be just small AA rechargeable batteries? What combinations can produce 5V? Maybe 3 pieces of 1.5v AA small batteries or 4 pieces? Remember I think each is only 1.2V?

#### rbelli1

Gold Member
Get an 8 way AA battery holder and use 8 lithium batteries with the DDR switching power supply. If the device actually draws 1A continuously you should get 2 or so hours out of them. Alkaline will be half or less life if they work at all.

The other option is to take the cover off the device and examine the internal power supply to see what is the acceptable range of input voltages.

You could also get a usb to whatever plug your equipment is cable and use that. The pictured adapter is 2.1x5.5.

For Example

BoB

Edit: you may have to choose a charging port on the computer for it to allow 1A to be drawn from it. Most new laptops will have all of the port with this capability. Look for a + next to the usb port.