Small system powering a GPS tracker

[leadfootlambert]

I do hope I am asking in the right thread, if not please forgive me.

Although I don't fully understand what is being said here, I think this may be the problem I am seeing. I am trying to power a GPS tracker in a device with no on board power and so purchased a 12 volts solar cell, Regulator and 'alarm type' sealed lead acid battery. Everything is working well under bench test over a number of weeks, apart from one thing - If I disconnect the solar cell (to simulate a couple of days without sun) the small battery eventually runs down, I assumed all I need do is reconnect it and after a few hours the tracker would start working again, but it does not because the Regulator is not charging the flat battery. Once I recharge the battery using a separate source, the Regulator eventually switches on and takes over charging.

I assumed it must be a duff Regulator and purchased a more expensive one with a inbuilt meter but this is doing the same thing. It is as if the panel does not have enough power (even in bright sunlight) to restart the stalled Regulator. If this is wrong please say and if it is right is there a calculation for the size of Solar cell to solve this problem please?

[sdold]

Hi Leadfootlambert, welcome to the forum. I moved this to its own topic. It might take a day or two for the admins to approve you for posting, but in the meantime I've approved this post and moved it to its own thread. It sounds like your battery doesn't have enough capacity to power the system through a couple of days of no sun. The charge controller may depend on the battery, not the panel, and if the battery is discharged too heavily it might not allow the controller to power back up when the sun is back. One thing to try is connecting the controller to the battery first, and then the panel.

Take a look here: https://www.solarpaneltalk.com/forum...s-why-tutorial

And here: https://www.solarpaneltalk.com/forum...battery-design

Steve

[Sunking]

First step is to know how many watt hours the GPS Tracker needs in a 24 hour period. I suspect not a lot, but the whole design depends on that. Once you have watt hours, you then select battery size to run five days, then select panel wattage and controller size.

However you do know to connect the battery before solar panels right?

Here is a reasonable example. GPS uses say 25 watt hours per day, and it runs off 12 volt battery.

Battery size = Daily Watt hours x 5 days / 12 volts. 25 wh x 5 / 12 volts = 10.41 AH round off to 10 AH is more than enough.

Battery will need a C/10 charge current and 1 amp is C/10 to a 10 AH battery. For such a small system you would not need a charge controller, just connect panel directly through a diode. Smallest PWM you can find is 5 amps if you want one. Or a 10-cent diode. Take your pick

Panel wattage all you would need 12 volt battery panel with a Imp of 1 amp or a 20 watt panel.

So find out how many watt hours the GPS uses in 24 hours. Real easy to do if DMM and a charge 12 volt battery. Just measure the current. Once you have that the formula is:

12 volts x Measure Current x 24 hours = Watt Hours.

Once you have that is super easy.

[leadfootlambert]

Thanks for the respons

The tracker has its own small battery and so to start with it draws around 0.180Amps but after the first couple of hours as the internal battery charges up, it drops down to a more or less constant 0.0280 Amps (apart from the brief moment where it sends a fix every 30 mins or so). The Battery is 12v 1,2Ah.

It just seems to me that if when the battery is connected to the Regulator first if it is flat no matter how much energy is being produced by the Solar Cell the Regulator will not start. If this is the case, is it manufactured like this or a fault ?

PS Below is a picture of what I have.

[leadfootlambert]

The system P1260671.JPG

[Kitsune]

My question is fairly similar to the OP.

What I would like to be able to do is have the ability to power a relatively low power netbook (33 watts) while in my car without tapping into the car's battery.
I have a 12 volt dc-dc power supply so should not need an inverter.- dc to dc transformers are generally more efficient.

I am thinking I probably want a 50 watt solar panel due to them never outputting their full wattage.
I probably also need a charge controller that produces 12 volts.
Would I want a small deep cycle battery? I realize that I would definitely need one if I am to use the netbook outside of peak sun times.

[Mike90250]

My question is fairly similar to the OP.

What I would like to be able to do is have the ability to power a relatively low power netbook (33 watts) while in my car without tapping into the car's battery.
I have a 12 volt dc-dc power supply so should not need an inverter.- dc to dc transformers are generally more efficient.

I am thinking I probably want a 50 watt solar panel due to them never outputting their full wattage.
I probably also need a charge controller that produces 12 volts.
Would I want a small deep cycle battery? I realize that I would definitely need one if I am to use the netbook outside of peak sun times.

Because of the electrical characteristic of a solar panel (no storage, current (not voltage) source, most DO-DC converters will not work with a small panel. If you had a 200w panel, that would have enough power to reliably run a small DC-DC

Behind window glass, tinted auto glass, or less than optimal sun angle, PV output will suffer greatly, so another reason to have to oversize the panel.

Why not use a panel to keep the car battery topped off, less complex, fewer parts