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# Need help on battery set up Answered

Hi All I am looking for a bit of help. I can't seem to find anyone to answer my question. We are working on an iot low power project that we plan to leave out in the field for up to 3 months at a time. We are using a Particle electron 3g module. It use 500ma per day when connected. It has two available power sources. 1 jst 3.7v port and 2 mini usb 5v - 12 v port. I am looking to make up a battery using lipo 18650 3.7v 2600amh components. Question 1. If I use the batteries in a 3s 13p set up I will have a 11.1v 38800mah battery, how long will battery last. ( I am getting the answer of 67 days from people but my question where dose the balance of the amp hours go as it is supplying power 11.1v and it only needs 5v to operate. How long will this take to charge and what is the quickest way to do this with out damaging the batteries. Question 2 Am I better using the 3.7v supply and stepping up the power on our mother board. If I do this I will build 39 of 3.7v 2600mah 18650 Lipos in parallel. How many days will this last for assuming that the step up module will work at 80% efficiency. How long will this take to charge and what is the quickest way to do this with out damaging the batteries. Sorry for such a long question but I can't get an answer. Peter

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I was having trouble understanding your power requirements, but you can
get 5 volt solar panels quite cheaply that will charge phone etc, If
you had a the right size panel on your device you leave it out in the
field indefinitely. It would also help if it gets cold as a battery
capacity can be decreased as the temperature drops.

How much energy does this gizmo want per day?

Does it want (3.7 V)*(500 mA*h)/day = 3.7*0.5*3600 = 6660 J/day ?

Does it want (5.0 V)*(500 mA*h)/day = 5.0*0.5*3600 = 9000 J/day ?

I do not at all follow what you are trying to say about how much power this device actually wants, particularly its voltage. Is it powered by a single Li-ion cell, and thus comfortable with battery voltage between 3.7 V, and some lower value, like 3.3, 3.0, 2.8?

Or is a device that wants 5.0 volts? And it has some sort of boost converter, that draws energy from a single Li-ion cell, at 2.8 to 3.7 volts, and converts that to a steady, continuous 5.0 volts?

Have you found these numbers based on measurements of voltage, current, and time, under realistic test conditions?

Or are these numbers based on numbers printed on the gizmo's name plate, or numbers found in its documentation, and estimates of the amount of time it will spend each day, phoning home, or sleeping, or gathering data on your enemies, or whatever it is that it does all day?

At the risk of me saying things that are obvious, I think the first case, i.e. measurements made under realistic test conditions, will give you numbers you can actually believe.

Hi Jack

Under test conditions it uses 500 ma at 5v per day. This includes sleeping, connecting, sending packets and power requires to turn on a notification led on the device.

We currently use a 5v 12000mah battery which is only lasting 3 weeks approx.

We need to use a larger battery and I am trying to figure out the best set up.

1 to use 39 x 3.7v 2600ma in parallel and step up (boast) the power to 5v on my mother board. My concerns for this type of set up is the time it could take to recharge the battery

2 to use 39 x 3.7v 2600ma batteries in a 3s13p set-up. This will give me an 11.1v is steeped down on the gizmo to 5v. My concerns is do i lose a huge amount of mah by 11.1v. But my understanding is that in this set-up it is quicker to charge.

Hope this makes sense

Peter

Hello Peter,

Regarding the thing you call, "5v 12000mah battery",

"We currently use a 5v 12000mah battery which is only lasting 3 weeks approx."

Am I correct in thinking that thing is not actually a battery? I mean, I am guessing it is one of those, so-called, "power bank", things, which is to say it is a battery (a network of cells), plus some power converter circuitry, a low voltage protection shutoff thingy, and maybe a charger too.

Have you ever pondered how this, "5v 12000mah battery", is storing its energy, and how it is converting its stored energy into a constant 5 volt output? How many cells do you suppose it has inside? Are its cells wired all in parallel, or with some in series?

Since the, "5v 12000mah battery" will power the gizmo for three weeks, presumably if it had 4 times this existing capacity, then it could power the gizmo for 12 weeks, or 3 months, which was the goal, right?

Regarding your question of how to wire 39 cells, either as 1s39p, or 3s13p, my intuition tells me that it would be simpler just to wire all 39 in parallel. Then use a boost converter to convert the voltage of 1 cell (approximately 3.7 V) to 5.0 V.

By the way, I am not quite picturing how it is that you recharge these cells.

Do you have them in cell holders, so that you can take the battery apart when you recharge it?

Or were you planning on permanently joining all of these individual cells together, like by welding little jumpers to all of them?

I mean if you had 39 cells all wired in parallel, I guess you would have to build a charger to charge them all in parallel, it would be kind of a big charging current to charge all these cells in parallel in a reasonable time.

I guess that is a recommendation. I mean, if you use cell holders, you will have a lot more freedom with regard to how you recharge the cells.

It would also give you some freedom in how you assemble the cells together. I mean you could try both arrangements: 1s39p with boost converter, and 3s13p with buck converter, to see which worked better.

Another thing I was going to mention is that you seem to keep writing mA (milliamperes), in place of mA*h (milliampere*hours), as if these were the same unit. They're not.

Although I guess it is not too confusing, if I can figure out which one you mean.

Jack