Boost LiPo up to 12V, or boost solar up to 12V? - Page 1
Forum section: electronics / projects

author: mrburnzie
author_rank: Regular Contributor
timestamp: June 30, 2019, 12:23:35 pm
content: Hello!I'm having a small issue regarding the 12V rail on my project.I have two options:- boost the 3.7V lipo (1S pack) battery up to 12V- boost the solar panel (5V) up to 12V (or 12.6V) to charge the 3S packThe 12V is used to power a motor.Most booster IC's are inefficient for 3.7V->12V conversion and don't allow a lot of current to flow.Boosting the solar panel is a good option, until I need a balancing circuit for the 3S pack.What do you recommend?

author: MosherIV
author_rank: Super Contributor
timestamp: June 30, 2019, 01:52:33 pm
content: QuoteCompletely inaccurate!Most modern boost converters are over 90% efficient.What you mean is that they do not produce the current you want.They are limited by power (P= V × I)If you tripple the voltage, you reduce the available current by 3.It is highly likey that the motor needs more power than the solar panel can deliver.The battery maybe able to deliver the power but as you realised you are going to need a boost converter capable of the current output.

author: mrburnzie
author_rank: Regular Contributor
timestamp: June 30, 2019, 02:08:28 pm
content: Okay, thanks for the clarification.Do you have any cost-effective booster IC you could recommend?

author: SiliconWizard
author_rank: Super Contributor
timestamp: June 30, 2019, 02:09:07 pm
content: How much power does the motor require (average/max)? This will help selecting the solution. Another question is: how much time would be acceptable for a full recharge of the battery?

author: mrburnzie
author_rank: Regular Contributor
timestamp: June 30, 2019, 02:11:22 pm
content: Average 1.2A, max 2A. The recharging role is just to keep the device alive. I'm looking into solutions to make everything as efficient as possible to keep the device up and running for a long time (1-2 years) on batteries (of course the solar panel is charging the batteries)

author: MarkR42
author_rank: Regular Contributor
timestamp: July 07, 2019, 09:30:31 pm
content: I use various modules described as "MT3608" boost converter to step up the voltage from a 2S lipo pack to >12V. These can be found on the usual outlets for a very low price. MT3608 is the control chip for the boost converter, the actual circuit has a few passives and a (very important) diode too.These are ok for >1 amp or so for a short period, it seems (at least, when boosting from ~7v to ~14v) (they are rated at 2A under some conditions)But they're mass produced and probably not well tested, they likely don't have good control over their BOM substitution etc, so I wouldn't be surprised if one batch work fine, and the next lot catch fire as soon as they're turned on.You could also roll your own board using the MT3608 chip and your own sourced diodes / caps / inductor which I assume would be more reliable (I haven't done this myself though).If you roll your own circuit to boost it, then you can connect the enable pin to an output on the microcontroller so you only boost the voltage when you want to run the motor, I suppose that will increase efficiency. I haven't measured the quiescent current of these modules.

author: ogden
author_rank: Super Contributor
timestamp: July 07, 2019, 09:49:02 pm
content: If motor can live with unregulated voltage coming from 3S LiPo cells, I would definitely drive it directly from battery pack and use boost (or buck) MPPT charger for solar panel.

author: Cosmic Osmo
author_rank: Newbie
timestamp: July 09, 2019, 03:12:53 pm
content: Are you really trying to run 1.2 A average @ 12v continuously 24/7? That is 346 Wh/day, and for reliability you want battery capacity for at least 72 hours, which is 1038 Wh. A 1S LiPo would need a capacity of ~280 Ah to deliver that. I don't think single cells even come that big, which means you're putting a bunch of them in parallel. Why not put them in series? You're going to need at least 200 watts of solar panels to keep this thing running, and such systems come at 12v nominal, if not more.