# 0.9v boost with Tp4056 for 6v Solar Panal?

Can I use it like this...

If so how can I limit my solar panel to only output 5v cause my booster can only handle up to 5v input.

• This should not be such a problem if the upconverter (booster) can handle 6 V, I mean that it will not be damaged by the 6 V. I have to know the type of chip it uses to be sure so include that in the question. The way most upconverters work is that with 6 V in also 6 V will come out, the circuit just cannot regulate the voltage anymore. However the TP4056 can handle up to 8V so 6 V will be fine, nothing will get damaged. Commented Jun 27, 2018 at 9:57
• A link to the booster board is needed. Commented Jun 27, 2018 at 10:02

I suspect that you will have some problems with this setup. Your solar panel may get up to 6+ volts under no load, but it doesn’t act like your typical voltage source holding to 6 volts and producing whatever current it can based on conditions. Under a load, the panel will produce LESS THAN 6 volts. You can look up an I-V curve of any solar panel to see how it works. So, depending on your load, your panel will output around 5 volts approximately, but that tp4056 tends to try to charge lithium batteries at 1000mA rate and when it tries to draw that high of a load from your panel that can only produce around 150mA at best conditions, funny things could happen.

It may just charge very slowly, or it may not charge at all, because when it tries to draw the large charge current, the voltage of the panel will drop, possibly below the 0.9 volt minimum and nothing happens. If the voltage doesn’t drop too low, then probable very very slow charging. Either way, the open circuit voltage of the panel of 6 volts, won’t happen when the panel is producing a current, so it is unlikely that too high a voltage will be your problem!

Good luck.

P.S. you have a 1 watt solar panel hooked to a dc-dc booster which might be 85% efficient, then the tp4056 bucks it down to the 3-4.2 volts that the battery needs, losing another 15% at least due to inefficiencies. So the max 1W panel can supply only 0.73 Watts to your battery under ideal conditions - a modern 18650 cylindrical lipo is easily 10 Watt-hours which means it would takes many days to charge a battery (given that you won’t get much more than 5-6 hours of perfect sun most days)

use a shunt regulator.

For a small panel (upto 250ma) a 2W 5,1V Zener Diode would work.

for a larger panel you'll probably want figure 19 from the TL431 data sheet use a heat-sink. perheps MJE2955 for the transistor.