# Smoothing a charging current for a phone?

Discussion in 'Power Electronics' started by tomadom, Nov 24, 2018.

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Jan 18, 2013
I raised a similar question some time ago about charging a phone with a solar charger or had cranked charger.
I later found that there are a number of USB Data line configurations for charging smartphones which vary depending on which region the phone was made.

To combat all these possibilities I ended up finding the below website explaining how to build a charging line bridge to get around the different charging configuration problems presented by various phones. Link below.
http://obddiag.net/usb-power.html

However, after building this, the phone still struggles to charge so I'm not thinking that the current just isn't stable enough.
I have been using a hand cranked generator and a solar panel to charge the phone and struggle to get a 1% rise in power.

How do I stabilize the current coming from my various chargers (solar and hand cranked)? I seem to remember someone mentioning bridging the + and - lines with a capacitor but surely there's more to this than that. What does a controller do? Is that what I need to get this to work?

Thanks. I'm a little stuck on this.

2. ### kellys_eye

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Jun 25, 2010
Since your supply source will vary between being 'too low' and being 'too high' you need a device called a buck-boost converter that delivers a stable output regardless of the input - providing you meet the minimum and maximum criteria the chosen module states.

3. ### Alec_t

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Jul 7, 2015
Assuming a phone battery capacity of ~3.3Ah at a voltage of 3.7V, full charge requires >12Wh of energy. If you can sustain, say, 3W output from a hand-cranked generator it will take over 4 hours to charge the phone, so it's not surprising it's a struggle. The buck-boost converter is a good idea, but sadly won't reduce the effort required. A bigger solar panel would help.

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Jan 18, 2013
buck-boost converter, this seems to be exactly what I need then. I agree that it will take a while to charge the phone with allot of effort. But it can be the difference between having no power at all and having power on the run if I need it.

Thanks for the help.

I don't suppose any of you could tell me if this item would work. My Solar panel outputs 5v and claims 7W output. The hand cranked generator will output anything from 3v to 28v 2-3 amps. Ebay and aliexpress have plenty of this kind of thing so I'm a little inundated. I'll have to connect a USB cable to this as well.
https://www.ebay.com.au/itm/LM2596-...b4c2c23e0:m:m6ZpUCmL6XNF8jprPO5DlaA:rk:3:pf:0

Last edited: Nov 24, 2018
5. ### kellys_eye

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Jun 25, 2010
Solar panel outputs are always, always stated as the 'best possible under the sunniest conditions' and rarely represent what you get in the real world. If you take HALF those stated values you'll be lucky to get them.....

The hand cranked output will be more realistic in terms of stated output but only by virtue of what you're prepared to put into it in the form of effort. Cranking for a few minutes seems possible but for long enough to charge (fully) a phone........

For either system, the length of time taken to charge the phone will depend on the power output from whatever system being used. Having a spare battery connected to a permanently mounted (and aimed) solar panel will potentially give you a power source when you need it (weather permitting) and I'd be more inclined to use the generator on a bike arrangement than a hand cranked version.

What situation will you be requiring the power in? Are there no possible alternatives to solar/hand cranking?

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Jan 18, 2013
No power points in the bush

Last edited: Nov 25, 2018
7. ### kellys_eye

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Jun 25, 2010
Not for me to question your use but personally I'd use the phone once a day to 'check in' otherwise keep it off unless for an emergency. With a spare battery (fully charged) you could go for a week(s?) without recharging.

Either way, given the 'bush' location I'd be looking at a bigger/better solar panel. Given they are 'flat' you should be able to pack a few into a small space - series connected to give a higher output and a buck converter to drop it to the required charging level.

8. ### Alec_t

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Jul 7, 2015
Probably no phone coverage either .

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Jan 18, 2013
Unfortunately I don't have the space.. I'm trying to get a basic mechanism of charging a phone to work. That's it.

It doesn't have to be great.

I posted a link for a buck boost converter above and was hoping someone who knows something about this could take a look and tell me if this is the right kind of thing I need. Trying to smooth the output current from a charger.

10. ### kellys_eye

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Jun 25, 2010
As per @Alec_t in post #3 you need 12Whr of energy. A 1W solar panel could do this in 12 hours or a 3W panel in 4 hours.

How long do you want it to take?

There are many 'geeky' solutions on the market such as this:

https://www.ebay.co.uk/itm/E0E3-15C...hash=item3fb1e3cffc:m:mnesRwuJQhIhYfksH191R6Q

which quotes 5V @1A output but I'd take that with a pinch of salt. But even if it was half that you're looking at a 6 hour charge period. Just hope it's as good as they state and you'll be done in 2-1/2!!

Use the search words "solar panel power bank usb" in eBay and have a look at 4,000-odd examples of similar stuff.

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Jan 18, 2013
Has anyone managed to look at the buck boost converter I posted. This being an electronics forum I'm wondering if anyone knows if these will do the job?

12. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Even a buck-boost converter may do you little good.

Unless you can generate sufficient power for the phone to use, it may not charge at all. Worse, the load may pull the output of the generator (solar or otherwise) down so that it actually can't provide power.

You are FAR better off using these various sources of energy to charge a battery (it need not be large) and use the battery to charge the phone. This will allow you to (say) charge the battery over a period of a day in order to provide enough power to charge the phone for an hour.

In that case you need an MPPT charger for the battery so that you most efficiently use the energy from your crank or your solar panel or whatever to charge the battery and then have an efficient charger that will run from the battery. If you could remove the battery from the phone you could cut out the middleman, but there's risks in that.

13. ### Alec_t

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Jul 7, 2015
I've never used one of those, but it looks promising. Whether or not it performs as advertised is another matter, but at only AU\$1 surely it's worth a gamble?

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Jan 18, 2013
Thank you for replying to my question. I agree too!

15. ### kellys_eye

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Jun 25, 2010
No comment on my post re the solar recharger link? (post #10)?

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Jan 18, 2013
Hi Kelly. Thanks for the reply.
I've been through every option there is for solar and hand generated power. I will have cell phone coverage but not all the time (as a poster mentioned above)

Solar and hand cranking is slow and tedious but it can get you out of a spot of trouble. That's the idea.
As far as the items you posted, those small solar chargers take way too long. I have a larger fold out 3 panel solar panel which works fine for charging a battery as you mention.

The whole point of this post was to work out how to smooth the currently going directly to the phone. Modern phones allow an uneven current feed into their charging usb port, but allot of these chinese phones (like mine) don't allow that so easily. That's why I have looked at smoothing the current so I can charge directly to the phone. I want to do this on the run because it simply saves time. I'll probably end up buying a phone with a larger battery too (Blackview BV9500, which has a 10,000 mah battery). To charge a battery and then the phone adds more time and I'm more than happy to charge the phone when it's switched off.

Directly to the battery does work though.

There are allot of products on the market for sure but most of the solar ones are terrible. They're all over quoted in terms of their power rating and a portion of those Chinese made things have pieces of plastic inserted to look like solar panels. I know this from experience.

I wanted orientate this thread for solving the charging directly to the phone problem and smoothing the current is the answer. There's an interesting link on my original post about USB Data line configurations for charging, which I've built and tried. Smoothing the current is the only thing I haven't tried.

Thanks for the input and suggestions.

17. ### BobK

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Jan 5, 2010
Phones expect a constant voltage of 4.5 to 5V to charge.

The only way to smooth the current is to accumulate the energy somewhere else before charging, like in another battery, which you have rejected. A supercapacitor would be the other option. Charge it until its voltage reaches 5V, then let it charge the phone until it falls to 4.5V. You could make this switching automatic. And size the supercapacitor so that it is able to charge the phone for some minimum time, like maybe 5 minutes.

Bob

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Jan 18, 2013
I'm going with the battery option after all, though when this buck booster arrives I'll hopefully get some results with that. I agree that the power needs to be stored somewhere and released at a constant rate (which is why a battery is good). In the end I'll probably just end up using a small power bank to get this to work constantly.

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Jan 18, 2013
I just thought I would add something. At this stage, I've come to the conclusion that it's just not reliable to charge the phone directly using one of these USB phone solar charges. The battery first is the only option as several of you have suggested.

I experimented with a battery pack ( usb power bank) and completely flattened it before I started. In the morning when the sun was bright I set the battery up to be charged by the solar panel, and then connected a usb lead from the power bank to the phone. It worked very well in the morning on this particular day, I had 10% extra in my phone in no time at all.

I used the flat power bank to see if it acted as an appropriate buffer for charging the phone. But when I tried it in the afternoon when the sun was still bright, but not as bright as it was in the morning, there just wasn't enough current cumming from the solar panels to charge the phone via the battery. Again I tried the afternoon charging with a flat power bank. I tried this with both a Goal Zero solar panel and another chines made panel I bought. The results were the same.

If there was some charge in the power bank it probably would have charged up the phone fine, but as soon as the power bank was drained this charging would stop unless I could get a high enough current from the solar panels to feed the phone via the power bank.

I'm not sure if even a buck boost converter would help here or not but I think that if it does, it would because it would never feed the phone or the battery an unstable current and the phone would readily accept in charging input as required.. Unfortunately, when the output from the panel dropped to 3.5 volts this may not even work, but I don't know this yet. . This is why I now think, as several of you have suggested, that charging a power bank is really the only option for me when travelling. That is, unless I carry an impractically large solar panel in my luggage.

Does anyone know if a buck-boost converter will help here?
Thanks

20. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Have I mentioned an MPPT charger yet? And you need to charge the battery directly. Charging a power bank via the USB charging port has the same inherent problems as directly charging the phone.

Something like this or this.