It didn't explode....... YET (aka niges amp)

[jkeny]

Yea, I have to play devil's advocate but your scheme will work fine running outputting lowish continuous current
A year proves it is working fine - what are you powering with it

[jrling]

I have started trying the concept with powering my audio PC (see signature). Low power CPU with DC power input. I run it at 12.5V on the guess that the CPU runs on 12V and may be therefore DC-DC conversion on the mobo for the CPU will be minimised if it is fed near 12v to start. I left it at 12.5V to allow for voltage loss in cable connectors etc along the way. Obv RAM and drives have DC-DC conversion down.

So that's 5 Supercaps in series running at their designed 2.5V fed by 4 A123 26650s running at 12.5V - 3.1V on each, which again is well within the spec voltage.

The PC draws 12W either at idle or when playing WTFPlay on Linux so that's 1A current draw, which is pretty minimal load for the PSU.

Compared with running the PC on the Maplin XM21X, the SuperCap/LiFePO4 PSU gave a very noticeable SQ benefit. Probably the best investment of time to build it I have made to date.

[nige2000]

Which super caps are u using johnathon?

[jrling]

Maxwell 350F 'D'cells
as here https://www.digikey.co.uk/product-detai ... ND/3079280

The pins give you possibility to hold them in place but relatively easy to solder without chance of damage from mega heat soldering iron.

The full account is here - Friday 6 July 6:01pm
viewtopic.php?f=15&t=3618&p=87780#p87780

[jkeny]

Very nice, jr - those 350F Maxwells are nice & what I use.
Nobody local bit on my supercap PS tour offer - ah well, I'll just have to tour it across the water

[nige2000]

Maxwell 350F 'D'cells
as here https://www.digikey.co.uk/product-detai ... ND/3079280

The pins give you possibility to hold them in place but relatively easy to solder without chance of damage from mega heat soldering iron.

The full account is here - Friday 6 July 6:01pm
viewtopic.php?f=15&t=3618&p=87780#p87780

got some supercaps yesterday in series charging shows imbalance, can you measure the voltage of the individual caps in your pack to satisfy my curiosity

[jkeny]

Oh, one thing occurred to me that could be another gotcha in this charging scenario - if the caps start off with different levels of charge (voltage) before starting charging then the resistor may not balance properly - allowing the cap with a head start to stay ahead & overcharge by the end of charge.

I believe that active balancing is the answer but I haven't seen many solutions that can balance higher current levels - I'm looking into a solution myself although the TL431 & Mosfet/transistor schematic posted earlier could do it once components are scaled up for higher currents.

Even in active charging there are a number of approaches
- continuously balance the charge between caps while the caps are being charged
- don't do this but rather stop a cap from charging once it has reached a set voltage
- use an isolated regulator for each cap

[jrling]

Maxwell 350F 'D'cells
as here https://www.digikey.co.uk/product-detai ... ND/3079280

The pins give you possibility to hold them in place but relatively easy to solder without chance of damage from mega heat soldering iron.

The full account is here - Friday 6 July 6:01pm
viewtopic.php?f=15&t=3618&p=87780#p87780

got some supercaps yesterday in series charging shows imbalance, can you measure the voltage of the individual caps in your pack to satisfy my curiosity

They all measure within 0.01V from each other. Have done for months with continuous float charging from A123 26650s and Maplin XM20X left on permanently.

Two questions -

• Have you soldered any passive balancing resistors between them as shown in my pix? If not, you will get imbalance.

• Did you use a high power resistor between the charger and the Supercaps to start with? I used a 100 ohm wirewound as I had one. After a while charging slows to a crawl and then I take it out of the charging circuit and it rapidly finishes getting to target voltage.

[nige2000]

Maxwell 350F 'D'cells
as here https://www.digikey.co.uk/product-detai ... ND/3079280

The pins give you possibility to hold them in place but relatively easy to solder without chance of damage from mega heat soldering iron.

The full account is here - Friday 6 July 6:01pm
viewtopic.php?f=15&t=3618&p=87780#p87780

got some supercaps yesterday in series charging shows imbalance, can you measure the voltage of the individual caps in your pack to satisfy my curiosity

They all measure within 0.01V from each other. Have done for months with continuous float charging from A123 26650s and Maplin XM20X left on permanently.

Two questions -

• Have you soldered any passive balancing resistors between them as shown in my pix? If not, you will get imbalance.

i did with 62ohm

• Did you use a high power resistor between the charger and the Supercaps to start with? I used a 100 ohm wirewound as I had one. After a while charging slows to a crawl and then I take it out of the charging circuit and it rapidly finishes getting to target voltage.

i didnt i charged at 5 amp one cell went to 2.4 the other to 2.6v which evened out over night, these caps are salvaged nesscaps i have, might need more testing to ensure there working correctly