# Hub Dynamo to 5v phone charger. Need advice on this project.

#### multifrag

Joined Sep 27, 2017
4
My goal is to make an efficient phone charger for long distance cycling. Last year I had a rough version of it which worked for the most part. I was wondering If I could make it better.

I tried to make it efficient by using buck converter and voltage doubler.
Have Over Voltage protection by using TVS diode and Thermal switch.
SMD components to minimize the footprint.

First problem I have is the Voltage doubler doesn't work. I must have understood it wrong. I've only tested the circuit on DC voltage, but the difference between input and output is ~ -1.5V.

Second is power delivery. I had power supply set up for up to 1A, but I couldn't get no higher than 0.5A. I might have messed up with resistor traces for iphone to detect the 1A current. Instead the iphone was only taking 0.1A. Android phone was taking 0.5A. Still not desired 1A.

Third is Buck converter. Even though I was only pulling 2.5W from MP2370 it got toasty(80C) From other reviews they could achieve 10W before going over 90C. Not sure if it is faulty buck converter or something else.

I would love to get some advice on the pcb design. Thank you very much in advance.

#### Attachments

• 41.7 KB Views: 4
• 289.3 KB Views: 2

#### Alec_t

Joined Sep 17, 2013
12,744
Welcome to AAC!
The voltage doubler does 'work', in the sense that with no load the voltage across the two capacitors would total roughly double the AC peak voltage (less diode losses). However, you would need much higher capacitor values to sustain that voltage if you want to draw any significant current.

#### multifrag

Joined Sep 27, 2017
4
Welcome to AAC!
The voltage doubler does 'work', in the sense that with no load the voltage across the two capacitors would total roughly double the AC peak voltage (less diode losses). However, you would need much higher capacitor values to sustain that voltage if you want to draw any significant current.
I was afraid of that. What capacitance do you reckon I would need? I might forget about the size and just go with functionality. The dynamo will produce ~5W of power.

#### Alec_t

Joined Sep 17, 2013
12,744
Here's a simulation using 1000uF caps. The dynamo is assumed to put out 5VAC peak at 20Hz. The output V(load) is shown for the situation where the load resistance is initially 10k then drops to 10Ω at the 0.5 sec point. You can see that even 1000uF is way too low to keep the voltage up around 9V.

Last edited:

#### multifrag

Joined Sep 27, 2017
4
Here's a simulation using 1000uF caps. The dynamo is assumed to put out 5VAC peak at 20Hz. The output V(load) is shown for the situation where the load resistance is initially 10k then drops to 10Ω at the 0.5 sec point. You can see that even 1000uF is way too low to keep the voltage up around 9V.
View attachment 137569
Thank you very much. The reason I was going for the voltage doubler is to start charging at lower speeds. Normally the dynamo kicks in the charge at around 15Km/h and with voltage doubler I was hoping I could lower it. Should I just scrap it?

What do you think Over voltage protection and smoothing the AC Voltage? Dynamo generates Voltage equal to bikes speed. I've noticed that going down hill I could easily be generating 50-60V AC.

#### Lyonspride

Joined Jan 6, 2014
137
Second is power delivery. I had power supply set up for up to 1A, but I couldn't get no higher than 0.5A. I might have messed up with resistor traces for iphone to detect the 1A current. Instead the iphone was only taking 0.1A. Android phone was taking 0.5A. Still not desired 1A.
Have you shorted together the data lines yet? Phones use this to detect USB charging versus AC charging....... USB locks to 500mA maximum.

I found the best way to get absolute max charging current is make your own charging cable using 0.5mm 2 core cable (because I have a 30m reel of it) and short the data lines at the connector end.
You can get USB connectors for next to nothing, I think I bought 50 of each for spare change.

#### multifrag

Joined Sep 27, 2017
4
Have you shorted together the data lines yet? Phones use this to detect USB charging versus AC charging....... USB locks to 500mA maximum.
I found the best way to get absolute max charging current is make your own charging cable using 0.5mm 2 core cable and short the data lines at the connector end.
I've made data lines read out 2V and 2.7V which is an apple 1A standard.

#### Lyonspride

Joined Jan 6, 2014
137
I've made data lines read out 2V and 2.7V which is an apple 1A standard.
That's the reason I won't buy Apple tbh, the lengths they go to in order to make it painful when not paying \$50 for a special approved USB lead.
My GF had a cable for connecting a camera to her iPad, but after an IOS update it no longer works, stating it's not a genuine Apple product.

I would say there is more to it that simply having the right voltage there, possibly even some data coms between the phone and charger, like an authentication key. I did read something about the data line voltages for Apple, seems you need high precision resistors to get the right values.

What I suggest will work with the Android phone, but I don't touch anything Apple

Last edited:

#### wayneh

Joined Sep 9, 2010
17,167
What I suggest will work with the Android phone...
Not all of them. Other manufacturers do the same as Apple. Well, not the same, just similar.