Hi, everyone. Was wondering if I could ask for some suggestions on an couple of issues.

I’m a senior Electrical Engineer student and am working on a team capstone project where we need to use solar power to recharge a set of batteries.
Our little contraption design, a box carrier with a shoulder strap, uses about 3W of power at 6V (that is full power consumption, but on average it will be much less than 1W): it's got a PSOC 4 microcontroller, a LCD display, maybe a little 400mW fan, and two 1.2W 12V miniature valves (we'll use a boost converter to step up from 6V). As of right now, we want to use a 6V 1mAh NiMH battery pack (as opposed to a LiPo battery).

The whole reason our team decided on NiMH batteries was because we read that they were safer and easier to handle and can be recharged more often, including when dealing with solar charging. Would you say that we could use LiPo batteries just as well? I ask just because we've been unable to find a definitely good charge controller for NiMH batteries that fits the bill (I'm losing confidence that NiMH was a good choice at this point).

We've been checking these solar panels and charge controllers: 6W Solar Panel (perhaps we could even go with their 3.5W version?) & LiPo Charge Controller from Adafruit, and this other solar panel with charge controller (is ok for 6V 1Ah NiMH batteries?) from Eco-Worthy.

So, we're trying to figure out which type of battery is best suited, and best charge controller for the job as well. I could provide more info on our project if needed.

Any suggestion or comment is very much appreciated!

Thanks,

Edgar

 

Since you mentioned a concern for safety, my only suggestion is that you consider lithium iron phosphate batteries, (and run from lithium polymer). but I'd only use genuine A123 cells, and be really careful who you buy them, it's a counterfeited product. LifePo cells from other companies are not (as far as I know) the same as the nanophosphate chemistry used by A123. A123 batteries are the only ones I consider reliably fire safe if your charger or something else goes nuts and tries to overheat them. But they cost more, and they are heavier than fire-prone lithium polymer and other lithium types.

Check them out at www.a123systems.com to see if they have a cell you can use. I think they have a link somewhere to their only real outlets on the internet, so there's no need to risk getting fakes from the abundance of web resellers that may or may not be selling the real product.

 

Lithium is and has been the rage for long enough now for its liabilities to be known. That said, NiMH has its own advantages, and I like it, and have used it with success.You've got to know, or establish the limits and priorities. You may find SLA to still be a viable option for the characteristics of your load and charge/discharge cycle!

 

Unless critical weight/energy density is an issue I prefer NiMh myself.

They have far less charge control issues to deal with (why you cant find a good charge controller for them is because they don't really need one unless you're doing high current fast charging) plus they are not heat sensitive like lithium tends to be either which where I live most lithium battery based cordless tool stuff stops working when used outdoors in the winter due to cold.

 

Thank you all three for your replies - that's awesome!

@tcmtechwe're planning on purchasing a 3W or 6W solar panel (here), and if we were to use NiMH batteries, we'd like to use a 6V 1Ah package. In this situation, would you say that we could simply bypass the charge controller with no issues?

Here's an image from what I understood: