Supercapacitors anyone?

[pootler]

pootler,
1. Are you using a Schottky diode?
2. The ammeter can add significant resistance. Try repeating the test without the ammeter, just monitor the voltage.
3. Make sure you have good solid connections.

a) Your video shows an immediate voltage drop from 5v to 4.15v. That suggests a standard silicon diode (not Schottky) and/or relatively high ammeter resistance. Even 1 ohm resistance is too high for this low-headroom circuit.
b) I am further troubled by the additional drop to 3.24v in roughly 3 seconds. That sounds like the caps are not really a total of 8 farads, more like under 3 farads.

Let us know what happens.
Frank

O.K

Shottky - Yes - see pic

2 x 5.5V 4 farad supercaps wired in parallel - yes - see pic You can ( just about) see the 5.5V 4 F on the side of the cap.

I do have a feeling that the voltage drop is less sudden if multimeter is not in circuit for reading current, however it still wouldn't explain the fact is doesn't work in the car?

If its important, i will do a vid of just voltage.

Many Thanks

pootler

 

[pootler]

O.K

Shottky - Yes - see pic

2 x 5.5V 4 farad supercaps wired in parallel - yes - see pic You can ( just about) see the 5.5V 4 F on the side of the cap.

I do have a feeling that the voltage drop is less sudden if multimeter is not in circuit for reading current, however it still wouldn't explain the fact is doesn't work in the car?

If its important, i will do a vid of just voltage.

Many Thanks

pootler

O.k

Checking just voltage - drops to 3.7 within a second similar to the video.

I don't quite understand - If I put the meter on the capacitors output, voltage also drops fast.

Does that mean they are crappy caps? - i didn't exactly spend a lot on them from ebay.

Cheers
pootler`

 

[Bluejets]

http://www.talkingelectronics.com/p... A Capacitor Works/How A Capacitor Works.html

 

[Frankchie]

pootler,
It sounds like your caps are sub-par, but let's backup for a moment.

I know you measured the current and the worst measurement said the current dropped from .45a to .4a after about 2 seconds. That current drop doesn't sound bad enough to cause the hub to fail, however your meter is probably not capturing the instantaneous drop that is probably more severe. That tells me that we only need to bridge a very small time gap when the instantaneous drops occur and a normal electrolytic cap might do the job.

Try bridging the 5v power to the hub with a common 1000uf or greater electrolytic cap. Don't use any resistors or diodes and don't use the super caps.

If that doesn't work, alternatively like Harald Kapp's idea, put that 1000+uf cap on the input to the hub fed through a diode from the existing hub battery supply. See attached sketch.

 

[Frankchie]

pootler,
I did some more calculations and I think a cap of at-least 10,000uf is probably needed. And using the 12v side probably has a greater chance of success. It all depends on the duration of the probable short dropouts that your meter has not detected. The internal resistance of standard electrolytic caps should prevent excessive charging current from causing problems. Don't use super caps.

Frank,
P.S. A while back you thought that a different accessory feed was more stable. Did you consider trying that feed and did that solve your problem?

 

[pootler]

pootler,
I did some more calculations and I think a cap of at-least 10,000uf is probably needed. And using the 12v side probably has a greater chance of success. It all depends on the duration of the probable short dropouts that your meter has not detected. The internal resistance of standard electrolytic caps should prevent excessive charging current from causing problems. Don't use super caps.

Frank,
P.S. A while back you thought that a different accessory feed was more stable. Did you consider trying that feed and did that solve your problem?

 

[pootler]

Hi Frank,

thanks for the reply,

I will look into what you are suggesting tomorrow ( different time zones )

Cheers

pootler

 

[pootler]

Slightly depressing update

So, tried the suggestions using the 10,00uF caps.
Sadly, didn't work at all
Tried 20,000 cap - also no luck.
Giving up on that.
Which is a bit fortuitous, because my windows car tablet has died.
Might look at android as there is much more development for car head units there.

Testing times
Thank you everyone for all your help.
Will update , if I get something working soon

Pootler

 

[Frankchie]

Pootler,
Sorry to hear that it didn't work. I have one more suggestion that may work. That is a simple lithium battery power bank, like those for charging phones. I believe some of them can act as a UPS for USB operation. I pretty sure not all power banks will transfer power seamlessly so you may want to research further. I have a power bank and it seems seamless judging from visual observation. Although visual observation is not a very scientific test of seamless power transfer.

Sounds like a great solution if you get the right power bank.

Good luck,
Frank

 

[dave9]

Someone has surely mentioned it already, but why don't you just tap into a circuit that is not switched off while the vehicle is cranking, or wire directly to the battery with a fuse added there if you're willing to suffer constant parasitic drain by leaving the 5V adapter plugged in, rather than a circuit only live in accessory or run state?

Modern automobiles have circuits that stay live and don't resort to supercaps, at least many don't.

 

[Martaine2005]

wire directly to the battery with a fuse added

Yeah, in post #16.
KISS

Martin

 

[pootler]

Someone has surely mentioned it already, but why don't you just tap into a circuit that is not switched off while the vehicle is cranking, or wire directly to the battery with a fuse added there if you're willing to suffer constant parasitic drain by leaving the 5V adapter plugged in, rather than a circuit only live in accessory or run state?

Modern automobiles have circuits that stay live and don't resort to supercaps, at least many don't.

 

[pootler]

Hi Dave9,

Thanks for the reply.

Yes you could - and then you have to have an external switch, so - as you say - the usb doesn't drain the battery if left for a few days.
I don't want another switch to have to turn on/off, and more importantly, neither does my other half . She will not remember to use it.
So I need to have a solid feed that is there during cranking , but is on the accessory circuit, so will go off when ignition is off.
The only feeds in my fusebox that do that are the accessory feeds, but they suffer serious voltage drop during cranking.

Anyway, as said, this is all on the back burner now that my tablet is broken.

Cheers - keep safe

pootler

 

[pootler]

Pootler,
Sorry to hear that it didn't work. I have one more suggestion that may work. That is a simple lithium battery power bank, like those for charging phones. I believe some of them can act as a UPS for USB operation. I pretty sure not all power banks will transfer power seamlessly so you may want to research further. I have a power bank and it seems seamless judging from visual observation. Although visual observation is not a very scientific test of seamless power transfer.

Sounds like a great solution if you get the right power bank.

Good luck,
Frank

 

[pootler]

Cheers frank - will have a look