Fake 2 Farad capacitors - more audiofoolery ?

[Fraser]

Whilst investigating the design of Capacitor Discharge battery tag welders, I stumbled upon a chap who had discovered the truth behind some of the "Crapacitors" commonly found in Audiofool car Hi-Fi installations.

Take a look towards the middle and bottom of the page. It makes interesting reading and viewing !

A small capacitor with some black pitch and part of a brick to add weight !

http://www.turtlesarehere.com/html/cd_welder.html

The author of the page opened two different brands of multi-Farad capacitor and they were both fraudulent in capacity claims.


Watch out, watch out, there's a Crapacitor about 

Fraser

[nukie]

If you are looking for one that works, look for those used Maxwell 2600farad 2.5v caps on eBay. They were used in hybrid bus. I have a batch they have very low esr suitable for series connection to increase voltage for suitable welding thickness. I think they are swiss made but I need to check the labels again.

[saturation]

Alas, one has to be careful buying expensive components off eBay because of the risk of counterfeit, particularly supercaps as they are expensive per piece.  Many eBay prices aren't that much better than a legitimate dealer like Mouser.

[nukie]

I'm suggesting the used ones, new units cost higher.

[Psi]

If you are looking for one that works, look for those used Maxwell 2600farad 2.5v caps on eBay. They were used in hybrid bus. I have a batch they have very low esr suitable for series connection to increase voltage for suitable welding thickness. I think they are swiss made but I need to check the labels again.

yeah, those maxwell caps are awesome.

I have 6 of them mounted in my car instead of a car battery at the moment.

[george graves]

yeah, those maxwell caps are awesome.

I have 6 of them mounted in my car instead of a car battery at the moment.

That I would like to see!

[smashedProton]

Psi, do tell!  What led you to want to install the caps?  Was it the terrible cca of lead acid, the environmental impact, or the crook battery salesmen?  How long can your car weight without your caps self discharging?  What do you do to charge them without blowing the ass out of your alternator?

[Psi]

Psi, do tell!  What led you to want to install the caps?

Car batteries in NZ are mostly made locally (unless you go for an expensive import brand battery).
Basically the local batteries are shit and designed to fail.
They last at most 3 years, and sometimes only 2, where as proper car batteries lasts 6-8 years.

I just got sick of having to replace my battery every 2-3 years so in went the six supercaps instead. They should last forever, more or less.
You just have to watch you don't run them flat by using accessories with the engine off, since the capacity is much less.
The engine sounds awesome when cranking, because the ESR is so low the voltage doesn't drop much under load. So the power going into the starter motor is higher and it turns over much faster.

Oh, and it stresses the charging system a little. The alternator tries to put all the energy removed during cranking back into the capacitor bank in a matter of seconds so it has a tendency to stall just after starting unless you give it a little gas.
I plan to fix that sometimes, maybe using a timed relay that adds some ESR for the alternator feed.
I also plan to add some 2.4V zeners in parallel to each capacitor, just to help balance the charge and make sure it doesn't overcharge one cap.
But so far that hasn't been a problem.

That I would like to see!

Fair enough, here's a pic

[smashedProton]

Sex on a stick 

[amspire]

I also plan to add some 2.4V zeners in parallel to each capacitor, just to help balance the charge and make sure it doesn't overcharge one cap.
But so far that hasn't been a problem.

The alternator can put out a lot of current and so if a zener starts conducting, it will have to be really heavy duty on a big heatsink.

A better approach would be to have a mosfet switch on each cap connected to a 1ohm 5w power resistor. It can then take its time equalizing the charge - it doesn't have to be done quickly.

[Psi]

I also plan to add some 2.4V zeners in parallel to each capacitor, just to help balance the charge and make sure it doesn't overcharge one cap.
But so far that hasn't been a problem.

The alternator can put out a lot of current and so if a zener starts conducting, it will have to be really heavy duty on a big heatsink.

A better approach would be to have a mosfet switch on each cap connected to a 1ohm 5w power resistor. It can then take its time equalizing the charge - it doesn't have to be done quickly.

All it needs to do is allow some of the energy to bypass any capacitor which is approaching full charged.
That way the voltage on other capacitors will rise faster that its voltage and the system will automatically find equilibrium.

I'll probably use a zener and resistor to limit current to zener Imax
I may run into the problem of zeners conducting below breakdown and draining the capacitors, so yeah, a mosfet maybe required.

[firewalker]

Go for mosfet and a voltage monitor (an opamp comparator). Or design a "smart thingy" to monitor voltages in an LCD inside the car, with low voltage alarm etc.

Alexander.

[amyk]

How long can you let the car sit without needing to charge the caps again?

The biggest drawback with supercaps is their high leakage relative to conventional batteries.

[Psi]

How long can you let the car sit without needing to charge the caps again?

The biggest drawback with supercaps is their high leakage relative to conventional batteries.

Actually, leakage is not an issue at all. People seem to expect supercaps to run flat quickly with zero load but that's not what i've found at all.

I ran a test to check this before starting the project. I charged up all caps to full voltage (2.5V) and left them for a few weeks.
Extrapolating the results the leakage was such that they wont have any problem staying above 80% charge for at least 2 months.
Keep in mind though, that the leakage reduces as they discharge so the leakage will never run them dead flat.

I charged up all 9 caps for the leakage test but only put 6 in the car. The other 3 have been sitting around since then.
So I just went now and checked them. They're at 2.13V  2.08V  2.01V
So they lost ~0.4V in about 6 months since they were charged.
Assuming in the car a full charge of 14.2V from the alternator, after 6 months with no load you'd expect about 11.8V

What IS an issue however, is the current draw from the car alarm, ECU memory refresh and cd/radio memory.
Because of those loads the car only lasts about 4-5 days of sitting around before the caps will fall below whats needed to start the engine.

I've not got around to actually measuring or fixing this issue because i already have a 14V DC charger in the garage which i setup a few years back so my carPC can run continuously while I program and test apps for it from inside the house.
I mounted a charge socket and LAN socket on the car so I've been keeping that charging socket plugged in so it hasn't been an issue.

I either have to reduce the cars standby current draw or install a cutoff relay to auto disconnect the dash power feed when the capacitor array falls below say 10V.

[nukie]

I can't believe it you replaced your lead acid with those boostcap. The caps are quite heavy but the battery is even heavier it probably help a bit with handling but most advantage is winter morning starts. These super caps are unlike your typical goldcaps, they store energy and they do it properly with very little leakage. I charged up two in series, a few weeks later I dropped a flat head screw driver and shorted the terminals, and the tip got eaten off in a flash! This taught me to discharge them right after playing.

Hats off to you being brave with these caps for engine start.

[Psi]

I can't believe it you replaced your lead acid with those boostcap. The caps are quite heavy but the battery is even heavier it probably help a bit with handling but most advantage is winter morning starts. These super caps are unlike your typical goldcaps, they store energy and they do it properly with very little leakage. Hats off to you being brave with these caps for engine start.

I remember when i did the swap i picked up the lead acid and the super cap array to check weight.
I couldn't tell any difference between the two so they're around the same weight.

Its quite common to have a lead acid coupled with a super cap array on really large trucks to help with cranking current on diesel engines in cold weather when the oil is so cold its thick as tar.

[nukie]

Can you install dashboard solar panels to help with the 'idle' current draw? Assuming there's sun where you park?

[Psi]

Can you install dashboard solar panels to help with the 'idle' current draw? Assuming there's sun where you park?

There's no sun in the garage obviously but yeah, that would help when parked in the open.
Currently i'm not sure how much current is being drawn and where exactly its going so reducing it maybe quite simple.

[tom66]

You could probably have use small backup lead acid, e.g. an alarm backup battery, and charge it through a small resistor trickling off the main cap bank, as the supply for the accessories. If you put a diode in series with the output and tied it to the point where the accessories connect, it would power the radio, clock, alarm etc. whilst not draining the main battery. I guess the main power comes through the accessory power relay(s) anyway. I don't know how much power they use, but I'd imagine under a few hundred mA in standby.

[Psi]

yeah, adding a battery is an option but i would prefer to just use capacitors for awesomeness.