Do I need a bigger battery?

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twelchptm
 
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Do I need a bigger battery?

Post by twelchptm »

I posted the findings of my latest project yesterday ( viewtopic.php?f=50&t=59906 ). I started putting my Pi-UPS w/ ISM to the real test yesterday, I started with a full battery and left the whole setup RPi and all on for 8 hours, then pulled the power and let the UPS do its thing. The pi shutdown and the UPS shut off the output power everything is good so far. When I got in this morning, I plugged it back in and everything started up perfect but around 11AM the battery went low and the pi shutdown. This revealed a critical flaw in my project, if the LB condition is not discovered right away the battery continues to drain until it can no longer support the ISM circuit and the Pi and the powerboost begin turning off and on erratically.
I am currently using a 2500mah LIPO battery (item #328) I think, but would like verification, if i upgrade to the 4400mah battery (item #354) the battery should last longer. I know this may not solve my problem entirly but if it will help i will do it.

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

Yes. All else being equal, the 4400mAh battery should give you about 75% longer run-time.

twelchptm
 
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Re: Do I need a bigger battery?

Post by twelchptm »

Okay, I am just learning about batteries and from what I have read on here about batteries I came up with this...

I plugged in my charger doctor at the wall, When I plug the battery and the ISM I built into the power boost, the charger doctor reports a draw of .43 A . When I plug everything in without the ISM it reports a draw of .4A . when the pi is shutdown and the enable on the PB is pulled to ground I don;t know how much extra is being pulled from the battery but the .03A that my ISM draws compared to the 2500 mah capacity of the battery means it should be able to run (theoretically) for 8,333 hours.

if my understanding is correct when the powerboost is plugged into the wall, power goes to whatever is plugged into it and the remaing power goes to the battery. my charger doctor reports that my RPi is drawing .4 amps, if the power boost has a charge rate of 500 mah i am recharging my battery for 8 hours at a rate of .1 ah and the ISM draws for 16 hours at .03 ah, I am replacing double what i am actually using. am i missing something? the battery i have should be fine right?

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

if the power boost has a charge rate of 500 mah i am recharging my battery for 8 hours at a rate of .1 ah and the ISM draws for 16 hours at .03 ah, I am replacing double what i am actually using. am i missing something?
mAh is a capacity, not a rate. And none of those power conversions is 100% efficient. The charger has a max charge rate of 500mA, but charge efficiency for LiPo cells is typically in the 80% ballpark, so for every 500mAh you put in, you will get about 400mAh out.. Then on the discharge side, you are boosting 3.7v to 5v, so there is a 25% hit there. Plus another percentage loss in the boost efficiency.

twelchptm
 
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Re: Do I need a bigger battery?

Post by twelchptm »

i think i understand, wold it be possible using the information i provided for you to recomend a battery for me? Or should I just go all out and get the 6600mah Lithium ion (#353)?

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

It sounds to me like you need both a larger battery and possibly a higher charge rate. If you are charging at 500mA for 8 hours at 80% efficiency, you would need at least a 3200mAh battery to hold the charge.

If you are still only breaking even with your discharge rate, you should consider increasing the charge rate. Most of our chargers can be programmed for up to a 1000mA charge rate by adding a resistor. The charger tutorial should have the details on what resistor size you need.

twelchptm
 
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Re: Do I need a bigger battery?

Post by twelchptm »

I how to increase the charge rate for the microlipo charger but not for the PowerBoost 500 Charger I am using, but from what i just read you are correct with a higher charge rate and bigger battery this won't work....

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

Unfortunately, the PowerBoost500C charge rate is not adjustable.

twelchptm
 
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Re: Do I need a bigger battery?

Post by twelchptm »

I have been digging through your forums while I await your response and think I may have figured something out. In one forum response it was mentioned that the charger item#390 has a load sharing circuit, and in another that the PowerBoost does not. So where the powerboost is charging only with what is left after powering the device, the 390 will power the device and charge the battery seperatly.
After this and a few other things I read I am thinking the PB 500 C may not be right for this project but if I seperate things a little using a 390 or charger #259 to run my battery and a powerboost basic to boost the output from the charger I can make it work.

questions - does the charger #259 have a load sharing circuit? are the #390 and/or #259 capable or switching from wall power to battery power as seamlessly as the PowerBoost 500 C? does adafruit have any plans for a PowerBoost that implements a load sharing circuit?

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

The #390 is the only charger we have with a true load-sharing circuit. The rest just wire the load in parallel with the battery. Many people have had luck with the #390 and a boost converter on the output.

I don't know of any PowerBoosts with load-sharing in the works at this time.

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Re: Do I need a bigger battery?

Post by twelchptm »

thats what i thought but wanted to be certain, the 390 with a PB on the output and then I can monitor the 390 with my ISM. I still think I should go a little bigger on the battery although it seems as though boosting the charge rate on the 390 and using my 2500mah batterie might cut it.

Now just throwing it out there.... a PowerBoost 1000 Charger w/ load sharing and intelligent shutdown output (so it will not only signal your device to shutdown but also turn its own input off and on) is something I would definatly pay for. Unless I figure it out first.....

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adafruit_support_bill
 
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Re: Do I need a bigger battery?

Post by adafruit_support_bill »

Thanks for the suggestion. I'll forward that to the design team.

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