TP4056 voltage adjust hack ? lipo charger  - Page 1
Forum section: electronics / projects

author: user1235423643
author_rank: Regular Contributor
timestamp: October 12, 2016, 02:16:10 pm
content: is it possible to modify one of these to have a different voltage output? 5v or 3v etc (like adding a pot or change res.)as it can have the constant current adjustedthankshttps://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdfhttp://lygte-info.dk/review/Review%20Charger%20TP4056%20UK.html

author: bktemp
author_rank: Super Contributor
timestamp: October 12, 2016, 02:30:32 pm
content: The output voltage is set intenally, only the current is adjustable.Why do you want to adjust the output voltage of a lipo charger?

author: user1235423643
author_rank: Regular Contributor
timestamp: October 12, 2016, 04:29:15 pm
content: i want to change the voltage few many reasons. one would be to fine tune or compensate for a diode drop in a project

author: Siwastaja
author_rank: Super Contributor
timestamp: October 12, 2016, 05:38:40 pm
content: Quote from: user1235423643 on October 12, 2016, 04:29:15 pmNot going to end well.

author: Audioguru
author_rank: Super Contributor
timestamp: October 13, 2016, 02:01:06 am
content: Quote from: user1235423643 on October 12, 2016, 04:29:15 pmA diode voltage drop changes when its current changes and when its temperature changes. So you do not want a diode in series between a lithium rechargeable battery and its charger circuit.

author: user1235423643
author_rank: Regular Contributor
timestamp: October 13, 2016, 10:34:27 am
content: dont bother commenting on this post if you have nothing worth saying.Quote from: Siwastaja on October 12, 2016, 05:38:40 pm

author: user1235423643
author_rank: Regular Contributor
timestamp: October 13, 2016, 10:35:17 am
content: thanks but would like to know if the voltage can be tweeked regardless,Quote from: Audioguru on October 13, 2016, 02:01:06 am

author: Skimask
author_rank: Super Contributor
timestamp: October 14, 2016, 12:59:59 am
content: You are, in fact, numb from the neck up, correct?

author: Buriedcode
author_rank: Super Contributor
timestamp: October 14, 2016, 01:13:20 am
content: I see no way of changing the peak voltage output, as the 'bat' pin is for both supplying current to the battery, and as a feedback node for its voltage. It is designed this way for good reason - the peak voltage of a lithium battery must be limited to prevent battery damage, overcharging, which can result in gassing/fire/fireworks.Having a separate pin to measure voltage and hoping the designer will connect it to the battery, or worse, have a lower voltage feedback (like 1.25V) and using a resistor divider not only adds an necessary pin, but also risks poor designs making batteries go pop - and then blaming the semiconductor manufacturer.You could use a bipolar power supply, say +/- 2.5V so you get 4.2-2.5 = 1.7V out, but its a lot of hassle for being able to adjust the voltage on a battery charger. Its specifically designed for lithium chemistries, if you have a different application, use something else.Also, as others have noted - if you have to compensate for a 'diode drop' you're putting a diode in the wrong place. There should never be a diode between the charger and battery *unless* there is a separate 'Vbatt' feedback pin that has a direct connection to the batteries anode. If you're working out how to have a power input both power your load, and charge the battery at the same time, there are various ways of doing this, but non involve a diode between the charger and battery.