Thanks for all your help @AlbertHall. You're an absolute star. I was soooo wrong with my initial "creation" !!!

I think I will go ahead and simply implement the setup you detailed in post #2. I have most of the bits anyway already. For R6, how do I go about making a 2Ω 110w resistor. Do I get a few and put them in parallel with each other or is there a particular one which you know of ?

[EDIT] I found a 100w 2Ω resistor on eBay (from China) so I've bought that - only 0.99p

The capacitors should be in parallel with the lamp not in series.
You will need balancing resistors across each capacitor to equalise the voltage as the capacitances will not be exactly equal.
You will probably also need a resistor to limit the charging current when you switch on, else it may blow the fuse.
It should look something like this:
View attachment 113968

Hi @AlbertHall

I have built the circuit now exactly as you have specified but twice in a row, it's blown the 5 Amp fuse. The circuit I'm using was originally the feed for the Car Radio.

What can I do ? Any suggestions greatly appreciated. R6 from your diagram is a 100w 1 Ohm resistor. I just notice now that I should have bought a 100w 2 Ohm Resistor. Could that be my problem ?

 

From your post #7, the fuse rating was 10A. Even with a 2Ω resistor the initial current will be 6A but not for very long so the fuse might survive.
You could either make R6 2.4Ω which will keep the peak current below 5A or try a slow blow fuse as the current peak is fairly short.

 

I've a 7.5A fuse so I'll try that now instead

Hi again @AlbertHall

I have a problem. Although it's actually working, the 5.6 Ohm resistors are basically heating up and burning, within about 2 minutes of turning on the power. I constructed everything exactly as you had it in your diagram.

Do I need to change the resistors or are my SuperCapacitors too large ?

 

The 5.6Ω resistors dissipate over 0.6W so they should be at least 1W rated.

 

Thanks @AlbertHall

How can I tell from the ones I have as to what rating they are ? They are Cream coloured, with the bands Green, Blue, Gold and then another Gold. They were supposedly 2W. The resistor centre is 1cm long

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Those resistors will get hot, but they do look like 2W so they should be fine - they certainly don't look burnt.

 

I pulled the plug on the source before they blew up. I was getting a smell from them.

Would a higher rating one (of the same value) be better ? I see 10w and 15w wire wound ceramic ones listed online

 

I can't see just how you've got that wired but a couple of things worry me.
The capacitors should be identical - you seem to have two different sizes.
You have two diodes, but there should be only one.
And this bit is my fault - the diodes don't look big enough. They have to be able to handle the load current so should be at least 3A for 25w load or 6A for 50W load.

 

Thanks @AlbertHall

Since Maplins only stock 2 x SuperCaps of one size at any time, I never got the chance to get 6 x 50uF and had bought 2 x 25 and 2 x 50 at one stage. I could go and change the 2 smaller ones now for 2 x 50uF ones.

I added the second diode to stop voltage feeding back to the source supply. I'll see about getting bigger ones so.

 

They have got to be the same capacitance or you risk blowing them up due to excess voltage.

 

They have got to be the same capacitance or you risk blowing them up due to excess voltage.

What wattage of Ceramic Resistors would you suggest ? Or are Ceramics the way to go ?

 

The resistors should be fine - sort the diode and the capacitors.

 

Hi

Why not try this simple & cheap circuit



To increase/decrease the time, increase/decrease the value of the capacitor or the 1M resistor.

Good Luck!

 

The resistors should be fine - sort the diode and the capacitors.

With the two smaller capacitors replaced and the larger diodes swapped too, everything is now installed into an enclosure and installed in the car, and it's working absolutely perfectly. Every time I turn off the ignition, it bridges the gap perfectly between the ignition off and the timer relay kicking in.

As you warned, the resistors do indeed get hot, but they are not absolutely burning up as before. I actually cut up the terminals strip allowing the caps to rest side by side in a long line.

Many thanks again @AlbertHall I'd never have got to this point without your kind asistance

Hey @AlbertHall , I'm back with a new but related problem, and I would be very grateful for your guidance and assistance.

I have bought a new PC for my car which, although it uses the same car charger to power it, must be requiring a higher ampage. The last was a Lenovo M53 now replaced by the more powerful M93. The mains transformer has an output of 3.25a @ 20v.

The issue I have with the new PC is that when I start the car, it momentarily drops the power. The last PC was fine so I just need to beef up the potential for slightly more power. Do I need bigger capacitors, resistor or diode - I'm clueless :-(. Just to remind you, the circuit is purely to hold the car 12v solid during fluctuations.

 

You would have to buy new capacitors and probably change the resistors too.
I think you would be well advised to use the circuit in post #35.

 

Many thanks for the speedy reply

What size of capacitor and resistor would you suggest - something which will cover things well and truely ?

Hi

Why not try this simple & cheap circuit

View attachment 115984

To increase/decrease the time, increase/decrease the value of the capacitor or the 1M resistor.

Good Luck!

Hi there,

Many thanks for this. What wattage should the resistors be ? Will this work for a heavy load ? And to increase the time, what values should the capacitor or resistor be increased to ?

 

You would have to buy new capacitors and probably change the resistors too.
I think you would be well advised to use the circuit in post #35.

Hi again @AlbertHall,

In a previous post you suggested that I needed to increase the size of my Diodes since the first ones I got were way too small. At the time, I then bought P600A Diodes / Rectifiers but with my new PC now using up to 8A @ 12v, would P1000A now do the job ?

 

It's a 10A diode so should be OK, but there's not much margin. 15A plus rated diodes would be more reliable.