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Hi Folks

 

Anyone got any ideas how to create a clean 12v supply on a car.

 

I now have several electronic devices on the car that really need a clean 12V supply, and I know that Dynamos and Voltage Regulators and Alternator supplies are variable at best and spikey at worst. I also discovered a month or two back that even things like simple timing strobes that plug into HT leads (rather than use an inductive clamp) can actually send very high voltage spikes back down their power supply cable to the battery.

 

So I'd like to create a clean 12v supply point, that I can enable when turning on ignition, but that is isolated from the voltage the battery sees, but ideally shares a common negative earth of the chassis/bodyshell.

 

So what I think I want is a small 12v to 12v transformer that I can switch on via a relay, and reconnect the negative of the output back to chassis ground. No large current requirements, think absolute max I require is 10 amps.

 

Would this work? any brighter ideas?

 

Alan

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The best solution would be a regulated switched mode power supply

Input voltage range - say 10 - 18V DC, Output voltage 12V DC

Such things are available, but could be pricy.

 

A cheaper option would be a low dropout voltage regulator which would need an input voltage minimum of 12.5V to give a sable output of 12V.

The price of these depends on how much current you wish to draw through it.

 

Have a look here: http://cpc.farnell.com/powerpax/3pwrb1209s-r2/dc-converter-3w-12v-in-9v-out/dp/PW03717?st=12vdc

http://uk.farnell.com/multicomp/mw201/converter-dc-to-dc-in-car-var/dp/1217060

 

Bob

 

 

Bob.

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You could do what you suggest Alan, using a dc-dc converter something like this:

https://www.amazon.co.uk/4-5-30V-1-30V-Converter-Power-Supply/dp/B00HV4EPG8/ref=sr_1_45?ie=UTF8&qid=1516538386&sr=8-45&keywords=12v+dc-dc+converter

It runs at a high frequency (300kHz) so the transformer is small and usually the ground is already common at the input and the output (but that will depend on the actual one chosen).

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Its amazing how cheap these sort of things are now - I've bought a few similar boards for various projects and they all seem to be well made and work just fine.

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Spot on

Cheaper here though if you only order one...and this supplier probably pays UK tax.

 

http://www.ebay.co.uk/itm/DC-to-DC-4-5-30V-to-1-30V-12A-Buck-Converter-Step-Down-LED-Car-Power-Supply-/192348986121?clk_rvr_id=1421104067542&rmvSB=true

 

Peter W

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Wow Guys, less than an hour to solution!

 

So excusing my electrical ignorance, it looks like the device that Peter posted, I hook up to to the cars 12v supply via a switched relay, and probably an inline 10 amp fuse, take the output supply (and presumably twiddle the little screw on the blue adjuster to set the output to 12v?)

 

Couple of quick questions it says

Overtemperature protection: Yes (overtemperature automatically switches off the output)

Input polarity protection: None (please install diode at input connector)

 

I'm assuming I don't have to worry about polarity protection if I get my +/- correct?

 

As its rated for 12 amps and the max I think I will ever draw is 10 amps and not continuous, do I have to worry about overtemp? only asking as I don't want a dead car on a hot day? Ensure I mount somewhere with air flow, think about a bigger heat sink?

 

Alan

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Alan

You will be tuning your vitesse between runs with a laptop if you carry on like this ?!?!?

???? + ???? = ????

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Wow Guys, less than an hour to solution!

 

So excusing my electrical ignorance, it looks like the device that Peter posted, I hook up to to the cars 12v supply via a switched relay, and probably an inline 10 amp fuse, take the output supply (and presumably twiddle the little screw on the blue adjuster to set the output to 12v?)

 

Yes thats right but if you are going to draw 10 amps use a bigger fuse to allow for the unit efficiency and to give a bit of margin. 15A should be fine.

 

Couple of quick questions it says

Overtemperature protection: Yes (overtemperature automatically switches off the output)

Input polarity protection: None (please install diode at input connector)

 

I'm assuming I don't have to worry about polarity protection if I get my +/- correct?

 

You DO have to get it right but if you do the diode is not necessary.

 

As its rated for 12 amps and the max I think I will ever draw is 10 amps and not continuous, do I have to worry about overtemp? only asking as I don't want a dead car on a hot day? Ensure I mount somewhere with air flow, think about a bigger heat sink?

 

The unit is quite efficient - they say 'up to 95%' but assume in the region of 80% at worst - so at full whack the heatsink may be dissipating up to 20 Watts. Enough to get hot in still air so it needs reasonable ventilation. When you enclose it, you need to ensure maximum air-flow so some sort of wire mesh or expanded metal cover would be good. It shouldn't be necessary to use a bigger heatsink but there's nothing to stop you doing that. Just check first that the heatsinks are not 'live'. ( They shouidn't be but you never know....)

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You will be tuning your vitesse between runs with a laptop if you carry on like this ?!?!?

 

Hoping for simple Street/Strip dash switch ;)

 

 

Wow Guys, less than an hour to solution!

 

Yes thats right but if you are going to draw 10 amps use a bigger fuse to allow for the unit efficiency and to give a bit of margin. 15A should be fine.

 

You DO have to get it right but if you do the diode is not necessary.

 

The unit is quite efficient - they say 'up to 95%' but assume in the region of 80% at worst - so at full whack the heatsink may be dissipating up to 20 Watts. Enough to get hot in still air so it needs reasonable ventilation. When you enclose it, you need to ensure maximum air-flow so some sort of wire mesh or expanded metal cover would be good. It shouldn't be necessary to use a bigger heatsink but there's nothing to stop you doing that. Just check first that the heatsinks are not 'live'. ( They shouidn't be but you never know....)

 

 

Thank's Rob that amount of solid input has probably paid for my TR Membership this year! I'd buy you a Pint but they have shut the Bar! :angry:

 

Alan

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As I said above John - its going to dissipate up to about 20 watts when supplying full current. The final temperature reached will depend on the air circulation around the heatsink but its possible they would be uncomfortable to touch for long under that condition.

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How hot will it get?

 

 

I suspect just for MJ ;) hardly at all, but I also want to drive the Innovate Datalogger that in turn supplies two wideband sensors which may well take 6-8 amps peak load. Also realised that I can use this as a clean supply for the little 12-5v converter I use to power TPS and MAP sensor.

 

Ah but you have made me think that I must go back and look at MJ wiring and decide if I need/want/have to feed EDIS or Coil Pack from same supply as the MJ, or if they only need to share common earth.

 

Alan

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Hello Alan

I ran Megajolt on Spitty for 5 years on a Lucas alternator with no problems!

I have run Microsquirt for 1 year admittedly on a Denso alternator(more output need for fuel pump) again with no problems!

I just assumed that the units have some sort of electrical filters built in as they are sold all over the world for people to fit on older car etc and people would have all sorts of trouble if not!

 

Plus surely all electronics are 5 volt so the power must be transformed in the units? and cleaned I assume?

 

Roger

 

ps not saying it would not help but more wiring if not needed and more bits to give trouble(cheap Chinese bits?)

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Hi Roger

 

Well I'm still running on a dynamo working on if it ain't broke don't fix it, (and I very rarely use lights) which I know can be spikier than alternators. However one of the reasons for a clean 12v supply is the Innovate kit, which on some of the logs is showing symptoms of spiky voltage, hanging the MJ off it is just extra caution.

 

When I said wow earlier in thread about quick answer to question, I have a double wow today, ordered item yesterday afternoon (Sunday) on eBay arrived by courier 11 am. this morning! £10.50 with Free Delivery! These Chinese are getting dam slick, or can they read minds? or have the Chinese government hacked the TR Register Forum?

 

Alan

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Hi Roger

 

Well I'm still running on a dynamo working on if it ain't broke don't fix it, (and I very rarely use lights) which I know can be spikier than alternators. However one of the reasons for a clean 12v supply is the Innovate kit, which on some of the logs is showing symptoms of spiky voltage, hanging the MJ off it is just extra caution.

 

When I said wow earlier in thread about quick answer to question, I have a double wow today, ordered item yesterday afternoon (Sunday) on eBay arrived by courier 11 am. this morning! £10.50 with Free Delivery! These Chinese are getting dam slick, or can they read minds? or have the Chinese government hacked the TR Register Forum?

 

Alan

 

Hello Alan

I do not think you can do a 12v and 5v off the same unit!

I may be wrong but I thought you need a higher voltage input than output not sure how much at a guess 1 volt!(I only run 24 v to 12 volt in our house)

I would feed the egr,s direct via double pole relay of say 20 amp

Roger

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I may be wrong but I thought you need a higher voltage input than output not sure how much at a guess 1 volt!(I only run 24 v to 12 volt in our house)

 

No Roger - with a buck-boost converter you can get more volts out than you put in, though of course the current is lower. (watts in = watts out plus losses) I think Alan is probably intending to use standard 12v to 5v converters from his 'clean' 12volt supply. Not really necessary of course as he could set the output of the dc-dc converter to 5v, but would need to wire up the equipment to run off that direct. Perhaps its easier to leave things as standard.

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No Roger - with a buck-boost converter you can get more volts out than you put in, though of course the current is lower. (watts in = watts out plus losses) I think Alan is probably intending to use standard 12v to 5v converters from his 'clean' 12volt supply. Not really necessary of course as he could set the output of the dc-dc converter to 5v, but would need to wire up the equipment to run off that direct. Perhaps its easier to leave things as standard.

Hello

Ok but that one say step down converter? Are there different types?

 

Roger

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Yes there are different types - this one is a buck converter but they quote input 4- 30v and output 1-30v so it should work if the spec is to be believed. As Alan is intending to use 12v (plus a bit ) in and 12v out that should be Ok .

Edited by RobH
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I think Alan is probably intending to use standard 12v to 5v converters from his 'clean' 12volt supply. Not really necessary of course as he could set the output of the dc-dc converter to 5v

 

Yes I already run some devices of a 12v to 5v converter, so my plan was get a clean 12v supply for the bits that need 12v and take a feed to the 12-5 converter from that as well, should be able to make a neat supply block and reduce the spaghetti a bit. I have always tried with the wiring to leave the standard loom intact in case at some point someone wanted to revert to plain vanilla.

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If my memory is correct.......a buck converter cannot raise the output voltage above the input.

 

However thats not a problem here if 12v is actually desired, as the electrical system will be operating above 12.0 v with the engine running.

 

My only concern is how much ‘margin’ the converter needs to operate, ie how close to the input voltage can it maintain the output voltage?

 

Steve

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Agreed that is of concern Steve but the published figures above do not state what the margin is. Since this unit is stated to give a maximum 30v output and the maximum input is 30v also, there would appear to be no margin required at least at that voltage if it is to be believed.

 

Problem is that there don't seem to be any equivalent buck-boost modules with the required current rating. You would have to use two and split the load between them. A purely boost module won't do because the margin works the other way so the output would be above the car voltage.

 

 

Alan - please note that I have found some data on the heat sinks of a similar-sized unit which states that additional heat sinking or fan cooling will be required if the modules are run at max output.

Edited by RobH
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