Powering an arduino and two servos using solar panel

Thread Starter

jquinton

Joined Oct 30, 2018
4
Hi

For my project I have to power an arduino and two servos using small solar panels (max around 111x90mm). It can be more than one panel but it has to fit on to a small area. My initial idea was to have a 5V DC-DC booster module to help produce a more consistent voltage and prevent backward voltage/current flow from the batteries, but I have come across a MPPT solar charger and I think that would do a better job to the booster module. The solar charger requires a liPo battery with charge greater than 450mAh and minimum of 6V. (A 3.5W solar panel is way too large!)

components with my project:
Arduino nano 5V
2x JX PDI-6221MG with Operating Speed (4.8V- 6V)
LiPo rechargable batteries
Solar panel


The problem I am having is finding a small enough solar panel which will at the very least meet the charging modules requirements. I can have more than one panel but I cant see another way around without compensating on either the voltage or current requirement.
I also haven't bought anything yet but I'm trying to gather my options- all suggestions are welcome. As you can probably tell - I'm new to electronics so if you can explain things as simply as possible it will help!
If you have anyother ideas please share!
 

wayneh

Joined Sep 9, 2010
16,286
Your panel is not a problem. Not for being too big, anyway. I’m not sure why you think it might be.

You don’t need MPPT for such a small project because the extra efficiency will never pay off the extra (small) cost. But, if that particular charger has other features you like, there’s nothing wrong with it.

Just make sure each item in the chain can handle the inputs it will see and produce the output you want. Check the power consumption of your servos. If they run very often, your battery will run down and the panel may not keep up.
 
Last edited:

Thread Starter

jquinton

Joined Oct 30, 2018
4
When I was looking at the specs for panels I noticed as the power rating increased the panel dimensions increased..this is why I kept on mentioning the size because I couldn’t find one with the right specs in various sizes.

I understand that I will be using the minimum in terms of energy capacity for the solar charger - which I am paying for - but I'm not aware of other charging/boosting modules that are quite like it. If I am cutting down costs, what do you recommend? The DC-DC 5V step up charger instead?

I don’t know the power consumption for the servos because I haven’t bought them yet to test it on a multimeter so I dont know the value for my load (that I am making) but I have the specs of the servos which I don't think will help?

Brand:JX
Item: PDI-6221MG 20KG Large Torque Digital Standard Servo
Dead band: 2μs
Working frequency: 1520μs / 330hz
Operating Speed (4.8V): 0.18 sec/60°
Operating Speed (6V): 0.16 sec/60°
Stall Torque (4.8V): 17.25 kg.cm (239.55oz/in)
Stall Torque (6V): 20.32 kg-cm (281.89 oz/in)
Dimensions: 40.5X20.2X38mm /1.59 X0.80X49 in
Weight: 62 g (2.18oz)
Connector Wire Length: JR 265 mm (10.43in)
Bearing: 2BB
Usage: For RC Models
 
Last edited by a moderator:

wayneh

Joined Sep 9, 2010
16,286
Well it’s crucial to understand the demands of the load as that dictates everything else. Will these servos be intermittent or continuously running?

It looks like the current draw when operating could easily be 2A or more. You’re little solar panel would be a waste of time.
 
Last edited:

Thread Starter

jquinton

Joined Oct 30, 2018
4
The servos will be intermittent and spontaneously run. Do you recommend I search for a different type of charging module where I'm getting more in terms of price range?

So if I my load equated to 2A, for example, are you saying I would have to be looking at a minimum of 7.4W (~10W) solar panel If I had 3.7V LiPo battery?

Also in the datasheet of the MPPT solar charger it says that it can be programmed to output up to 2A. Would I need to find a module that can output a higher Amp range just incase the load does require a higher A?
 

wayneh

Joined Sep 9, 2010
16,286
The servos will be intermittent and spontaneously run. Do you recommend I search for a different type of charging module where I'm getting more in terms of price range?

So if I my load equated to 2A, for example, are you saying I would have to be looking at a minimum of 7.4W (~10W) solar panel If I had 3.7V LiPo battery?
Since they will run intermittently, it's more complicated than that. One way to view the situation is to start with the acceptable probability of inadequate power. This might happen after 3 cloudy weeks in January, for instance. The batteries are deeply discharged and freezing cold on top of that. The panel might have snow on it. If it's mission-critical for your device to still have power in that worst-case scenario, you obviously need a much larger panel than a scenario where you only expect the thing to run on mostly sunny days, and it's OK if it goes dead every night and occasionally on cloudy days.

The first chore is still to estimate the daily power consumption. Any estimate is better than no estimate. Then you need to consider what your panel can really produce, on average, per day. This depends on the sunshine levels where you live, whether the panel tracks the sun or not and a bunch of related factors. There are online tools that you can use to estimate all this. They won't be perfect but far better than nothing.

Also in the datasheet of the MPPT solar charger it says that it can be programmed to output up to 2A. Would I need to find a module that can output a higher Amp range just incase the load does require a higher A?
It might be OK, if you've determined that charging the battery at 2A is acceptable. If your analysis above shows you really need to allow for higher current at peak sunlight, then 2A is obviously not enough. The servos might draw quite a bit more than 2A at the instant they start up (or get stalled by reaching the end of their travel?), but that's what the battery is for.

Whatever panel capacity seems reasonable for your project, consider doubling it. That makes up for "optimistic" specs from the manufacturer, for less-than full illumination, dirt on the panel, panel aging, and so on.
 

Thread Starter

jquinton

Joined Oct 30, 2018
4
The first chore is still to estimate the daily power consumption. Any estimate is better than no estimate. Then you need to consider what your panel can really produce, on average, per day. This depends on the sunshine levels where you live, whether the panel tracks the sun or not and a bunch of related factors. There are online tools that you can use to estimate all this. They won't be perfect but far better than nothing.
Its a good base line to think of the daily consumption. I think a good estimate for daily use is up to 3-5 hours a day. It will not be used for that long but I think its a safe average measurement.The device also will not have any loads added to it.
I've researched how to calculate daily power consumption but they all start off with knowing the Watts of the device. I don't know how much Watts I will require because current isn't stated in the datasheet for my servos. Not sure how else I could calculate daily consumption from the servo spec above.
However, I've seen a pretty expensive servo which has a no-load current drain of 400-500mA that has slightly lower specs than the one above so I think a 2A charger programmable up to 2A should be more than enough. That would mean I'd need a at least a 2W solar panel for a 4.8V input (do I double this because I'm using 2 servos or will the solar charger "boost" it?)

(Side note: the device is just a prototype/concept where I'm trying to focus on powering the device and having it perform the functions thats in the objectives. It will not be used for large periods throuoghout the day but only really for project use. Then it is shown to perform the desired functions, more focus will be drawn to incorporating it in real life daily use in future developments but overall, the aim is for it to be used in sunnier climates.)
 
Top