Can this be an effective voltage stabilisation for cars?

[Hattee]

Serious designs to improve voltage quality in automobile inevitably have to focus on the cyclical surge in power demand particularly from ignition. Such surge is barely met by most alternator-battery designs at rapid rpm changes and as battery ages. Any effective stabilisation of voltage cyclical transcient will certainly benefit the engine at idling and acceleration, often improves FC and its overall cleanliness.

 

For ignition transcient from 850rpm-3600rpm acceleration in 4-cyclinder induction,

Cyclical trancient stabilisation has to be effective up to 120 sparks per sec for 4-stroke

= 120 Hz (typical elect capacitor rated ripple frequency)

= 8.4ms approx

 

For design of voltage stabiliser, recovery at every cycle for the stabiliser must not take longer than the RC time-constant. This recovery is necessary for the capacitor to be charged up before it can be effective to stabilise the voltage in the next cycle.

 

60,000uF -10% +75% rated at 105deg C

Design assumes C=60,000uF*

 

0.008ohm ESR rated at 105deg C

Design assumes ESR=0.01 ohm

 

Resistance of 1m single-core cable (better than soldered/crimpled)

Design estimates Rcable=0.10 ohm

 

Assume 1.5V volt-drop (momentarily unregulated) at 50A (600W)

Estimated alternator/battery internal resistance Rsource=1.5/50

=0.03 ohm

 

With Rtotal=0.01+0.10+0.03=0.14ohm

RC Time-constant=0.14 ohm x 0.06F

= 0.0084s

= 8.4ms approx

 

CAPACITANCE.............ALLOWABLE CHARGING RESISTANCE

120,000uF**.............0.069ohm

60,000uF*................0.138ohm

30,000uF***.............0.278ohm

10,000uF***.............0.833ohm

 

* capacitance with longest time-constant for possible effective voltage stabilisation based on the above assumptions.

 

 

SOME CONTRAINTS IN DESIGN OF VOLTAGE STABILISATION FOR AUTOMOBILE

 

1. **TOO LARGE CAPACITANCE Large capacitance will not satisfy the RC time-constant from the worst-case cable plus alternator/battery resistance eg 120,000uF would require very low 0.069ohm charging circuit resistance not easily attained without very thick wire, low resistance connecting contact, bigger alternator and battery. Once the time-constant exceeds the required period of cyclical transcient, the capacitor will not have enough time to recover the needed energy to stabilise voltage.

 

2. ***TOO SMALL CAPACITNACE Smaller capacitance has larger ESR and less than the minimum 20A ripple handling capability. Hence, it may not be effective enough in voltage stabilisation although it has shorter RC time-constant.

 

3. HIGHER RPM CONSIDERATION At higher rpm, the ignition transcient is shorter. It requires even shorter RC time-constant, hence, smaller capacitor and lower circuit resistance. Lower ripple current and lower circuit resistance becomes design constraints (however, typical street acceleration seldom exceeds 3600rpm).

 

4. EXPENSIVE LOW ESR 105 deg C low ESR capacitor of greater than 25,000uF are expensive (60,000uF can cost SGD50-100). The usual 100%-500% profit margin will prohibit some designers to use such capacitor eg.

http://www.rssingapore.com/cgi-bin/bv/rsww...=sgie&Nr=avl:sg

 

5. HEAT IN ENGINE BAY Furthermore, the high temperature from the engine bay is never suitable to house electrolytic capacitor. A capacitor may be rated at 125 deg C. Its ripple current handling capability is only a fraction of its rating at elevated temperature. In addition, increase leakage current is detrimental to voltage stabilisation. Worst will be the shortening of useful life when capacitor is subjected to prolonged heat close to its max temperature. Proper thermal insulation is essential to ensure voltage stabiliser is not just useful for the first 1000hrs (12 month).

 

6. TOO LONG CABLE Routing of capacitor to the cooler cabin is not recommended because of the longer cable which introduces substantial resistance. Otherwise the larger RC time-constant or use of lower capacitance will not be effective for voltage stabilisation.

 

Then, is it necessary for a good voltage stabiliser to cost $90-$900?

[Diesel]

Some VS are "invented" at homes, slapped with a cool label & sold for over a hundred bucks...

[Wishsing]

uhmm.. another "Myth" busted?? haha. we should have a thread on "Snake Oils"

[Dermocyma]

Finally we have a scientific way to explain clearly what voltage stabilizer is all about. Please share with us what are your findings and more research.

 

"is it necessary for a good voltage stabiliser to cost $90-$900?"

 

my answer, as i experiment out of curiosity using 2 brands of VS on cars lower than 1.6L 4I 55Ah battery and 3.0L V6 100Ah battery, weeks on, only the former can 'feel' the placebo effect but not on the 3.0L vehicle. these placebo effect are those indicated in advertisement. having said the above, it is observed both vehicles subsequently behaves with the same placebo effect after the VS are removed from vehicle. It seems, from a layman perspective, both vehicle onboard ECU seems to have adapted to whatever the VS provides and dont require them anymore. Can you or anyone validate this claim.

 

Also, one of my concern all along is the temperature in engine bay and its effects on the normal operation of VS. I read on commercial (non military spec) electrolytics are bad for high temp operation and melts on overheating. What you highlighted could also explain the reason why some of the VS gave instant graftication on overall vehicle performance but somehow suddenly after several weeks, the improvement 'disappear' or like what many VS veteran like myself say 'the butt got used to the enhancement liao'

 

It is definitely worthy to investigate more into this. I know for sure SPRING will be able to bring it to a higher level if there are concrete discovery on anyone part with regards to this VS idea.

[Zrun]

For 90% of car users out there, not needed.

 

You won't get noticeable increase in fuel mileage, and with the prevalence of scams, it is not worth it to venture into this.

 

Strict enthusiasts who wants the extra 1-2 hp can pay for this, but strict caution is needed. It is better to buy from well known makers that are well accepted by the global market. Forget about local, single snake oil product marketers.

Edited October 31, 2006 by Zrun

[Hattee]

Did replace a popular VS with a low-ESR 60,000uF using thick single-core cable. Acceleration is even smoother than this VS. Seems to notice acceleration can continue with no further down stepping of throttle from 2000rpm. Downside is the engine heated the capacitor to 60-80 deg C after 30 mins drive. Not too comfortable and now looking for a correct sized COTS thermal pack to house the capacitor.

 

Some may claim of preventing power loss to overchanging battery by some kind of voltage strapping. Personally, its effectiveness all boils down to the capacity of its capacitor and the circuit time-constant. Perhaps, it can be useful to some extend if the capacitor is large enough with adequately low ESR to keep and give enough charges in order to sustain the voltage for a certain load transient profile.

[Dermocyma]

That is a big-ass capacitor. how much and where to get a 60F unit? how many are required in parallel and is it necessary to be electrolytic? COTS boxes like those from SLT?

[Normal_aspirated]

no lah, it's 60,000 micro-farad.

works well on my mazzie 323 protege.

[Hattee]

I meant 0.06F. If you put a typical ICE 1-Farad to calculate RC time-constant, the capacitor probably can't even handle any load higher than 10Hz unless cable resistance plus ESR plus battery internal resistance is extremely low.

[Dermocyma]

may i ask how many of these 60000 uf capacitors do i need to experience what u said.

[Normal_aspirated]

6pcs of 10,000uF each.......all in parallel.

[Dermocyma]

i understand some VS combine electrolytic cap with ceramics and polymers. especially those strung up together using solders lead. any reason on that? doesnt naked exposed lead between capacitors create noise and harmonics?

[Normal_aspirated]

electrolytic caps do hv some inductance within itself, low value ceramic/polymer caps will help filter high frequencies if any......

[Dermocyma]

great thanks. i was thinking, how much would it cost you to build a superduper version of a VS with thick wire from Sim Lim Tower components.

[Hattee]

Maybe you can get a 60000uF from RS for $81:

 

http://www.rssingapore.com/cgi-bin/bv/rsww...=sgie&Nr=avl:sg

 

But dunno issit low ESR (equiv series resistance). Impedance and Inductancce not an issue with frequency below 200Hz. Problem now is Sim Lim Tower has less discrete components than 20 years ago. 60,000uF 35VDC 105 deg C hard to come by. Even harder if looking for low ESR of 0.004-0.008 ohm. Much easier to find 1 Farad.

 

Brought back mine from US. I do have some 2.5mm single core cable.

Edited November 7, 2006 by Hattee

[Dermocyma]

indeed very good observation. thanks for the link.

 

do u agree that when it comes to price vs efficiency matter, wouldnt it take a little compromise for the VS to be manufactured much easier? I have observed various VS and found the components used are general-purpose unit, can that be the reason why most VS create 'placebo effect' and nice butt dyno feel initially but as component 'weaken', our butt get used to the nice feeling. would like to hear your view on this.

 

If I am not wrong, those 1F cap are used for audio equipment?

[Hattee]

You are right, capacitor used in most off-the-shelf VS are alot smaller and unlikely the low ESR type. Not a fault of the producers cos it's very competitive and most of them needs 200%-500% profit from producer, retailer to buyer. Perhaps, anything bigger than 0.12F unlikely will not work very well as VS without radically thick cable, large alternator and battery.

 

Few producers will seriously consider the potential deteriorated VS performance and its capacitor life at elevated temperature. Most electrolytic capacitors suffer from reduced ripple hamdling capability in the engine bay with eventual shorter life span if they are not adequately insulated. I found a thermopack and probably will fix up this weekend.

 

Just come across some interesting information about capacitor at http://www.cde.com/catalogs/AEappGUIDE.pdf .

Edited November 11, 2006 by Hattee

[Spikedoll]

meaning mostly cap with smaller size as in 1608 1.6mm x 0.8mmwith low capacitance temperature characteristics..low voltage Edc like 10v?..u know the pF ?