voltage drop in powerboost 1000c on o/p

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nayan_agg
 
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voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

HI,

i'm using powerboost 1000c to power up my pi3 with li-ion pack & through adapter.
when i checked o/p from powerboost 1000c it showed v= 5.13 which is normal. But when i connect my pi3 with it the voltage dropped to 4.5V which is unsual coz it makes my pi3 to reboot again & again.

Halp!

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adafruit_support_mike
 
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Re: voltage drop in powerboost 1000c on o/p

Post by adafruit_support_mike »

Do you have anything connected to the Pi3 that would also be powered from the PowerBoost?

The 1000C has a hard upper limit of 1.1A output current. Anything higher will kill the MCP73871 LiPo charger and make the board useless. A Pi3 can use up to 800mA by itself when all four cores are active, leaving only 300mA for anything else that might be connected.

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nayan_agg
 
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Re: voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

Hi mike,

Only official raspberry pi 7 inch display & ds18b20 temp. sensor probe is connected to pi 3.
i've also checked the current consume on start up was b/w 700mA to 1A.

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adafruit_support_mike
 
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Re: voltage drop in powerboost 1000c on o/p

Post by adafruit_support_mike »

A Pi3 with the 7" display crosses the PowerBoost 1000C's output limits. We've seen that happen before.

The system will work as long as the CPU load is fairly light, but at higher CPU loads the current consumption is higher than the 1000C can handle.

Digital systems tend to have choppy current requirements, and multimeters are slow. My guess is that the 1A level you've measured has fast peaks higher than 1.1A, and the 4.5v is an average between the highest and lowest peaks.

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nayan_agg
 
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Re: voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

Hi Mike,
Thanks for the reply!

powerboost 1000c has load sharing feature as i've 5.2V 2.5A adapter connected to powerboost 1000c and li-ion battery. still it is not giving full o/p.

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nayan_agg
 
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Re: voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

I again test it combining both pi3 & 7 inch display. it consumes b/w 900mA to 1A.

while booting pi3 alone it consumes 400mA. & only 7 inch display consumes 510mA. So, according to your powerboost 1000c description it says that 5.2V 1A+ o/p. while mine is only 1A. Then why voltage drop? kindely clarify!

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Re: voltage drop in powerboost 1000c on o/p

Post by adafruit_support_mike »

The specs of the wall supply don't really matter.

The MCP73871's internal load-sharing switch has an absolute upper limit of 1800mA, and the TPS61090's burst current requirements when charging the inductor pull the load-shared output voltage down to the LiPo voltage under all possible operating conditions. The limiting numbers are 1800mA @ 3.7v and 95% efficiency, and those cap the absolute maximum output at 1.1A @ 5v.

'Absolute maximum' doesn't mean 'everything will work normally up to that level and then stop'. It means 'that's as far as you can push the hardware without destroying it'. That much current generates heat, and both the MCP73871 and the MCP61090 have thermal protection circuits that throttle the current back when the chip temperature approaches 100C. If your assembly limits airflow across the chips, they won't be able to dump heat fast enough to operate at their absolute limit.

Also, as I mentioned above, if you're measuring the RasPi and display current at 1A, there are peaks higher than 1A that are too fast for your meter to measure. If you have access to an oscilloscope, probe the Vs pin with the timebase set to about 10us per division. In normal operation the TPS61090 switches at about 40kHz, so that's where you'll see the spikes and dips that limit the PowerBoost's performance.

Bottom line, many people have built projects using a Pi3, the 7" display, and a PowerBoost 1000C, and all of them have seen the system act flaky. it's a known issue with that combination of parts.

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nayan_agg
 
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Re: voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

Hi mike,
I supplied 5V seprately to pi 3 & display from PB 1000c and it worked now the voltage drop is not happening. But know the issue again arises is that when I connect power adapter of 5.25V 2A to PB 1000c for charging the o/p voltage again drops. kindly suggest!

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Re: voltage drop in powerboost 1000c on o/p

Post by adafruit_support_mike »

The only suggestion I have is to stop trying to power a Pi3 and 7" display from a PowerBoost 1000C.

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svorkoetter
 
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Re: voltage drop in powerboost 1000c on o/p

Post by svorkoetter »

FWIW, I'm having zero issues powering a Pi 3, 7" display, RTC, and USB audio, from a PB 1000C and 6200mAh LiPoly, either plugged in or not.

With the Pi idle and the display brightness at 212, current consumption is 0.86A.

With the Pi playing a YouTube video and the display brightness at 42 (about 50% perceptual brightness), current consumption is 0.55A.

As I mentioned to the OP when he posted on my blog, the wires from the battery to the PB 1000C need to be short and/or thick, and the wall adapter, when used, needs to be able to supply a solid 5V at 2A.

I would be curious to know the measured PB 1000C _input_ voltage from the wall adapter when the output is dropping to 4.5V. I suspect that the adapter voltage is dropping under the dual load of powering the Pi/display and charging the battery, since it's working fine for the OP when the adapter is _not_ connected.

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Re: voltage drop in powerboost 1000c on o/p

Post by adafruit_support_mike »

As you've shown, it's possible to make that combination of parts work, but only if you're careful to keep the current load well within the PowerBoost 1000C's limits.

The same hardware can easily overpower a PowerBoost 1000C, and we've seen too many people kill a board that way to recommend it as a general solution.

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nayan_agg
 
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Re: voltage drop in powerboost 1000c on o/p

Post by nayan_agg »

90% of my issues with PB 1000c is over. Thanks to Stefan!

The only issue left is that when connected to wall adapter the o/p volts drops which is probably due to poor wall adapter which I'm replacing with better one.

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Re: voltage drop in powerboost 1000c on o/p

Post by svorkoetter »

I guess in general, it would be best to use a separate PB 1000c (used as a boost converter only, not a charger) to power the screen. Would the two PB 1000c's interact badly in any way?

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