LED lights

[Gibbo]

This is actually getting quite funny.........

 

I feel that you are determined to repeatedly point out that there is no perfect solution - something I have totally agreed with. The lack of a perfect solution is however no reason not to implement a compromise solution which has adequate effectiveness. Engineering is all about compromise and setting the right compromise in this case (ie effectiveness vs cost) seems to me to point at the Transzorb solution.

 

All I can say is when I first started in the field of transients on vehicles and DC systems I would have said the same. In fact I did say the same. I soon learnt when everything blew up after a few months, failed testing and type approval and caused us lots of expense with warranty claims. I made it my business to go and learn about the problem (a problem which many people either don't even realise exists or believe is a lot simpler to crack than it is) and not make any assumptions. I'll further add that you will eventually come round to agree with me. Of that I have absolutely no doubt. Unless you simply never learn.

 

Regarding the energy spec on the datasheet, sorry I did not read your post properly but I feel that since the exact spec of the transient is not known, getting too far into calculations is not necessary

 

But the calculations do prove the point that the ISFM rating, in conjunction with Vf at that current massively exceeds the small scale maximum energy rating for the junction so it goes bang due to current hogging. Almost immediately.

 

- one just specifies a diode with a surge current greater than the guestimated transient current, with a good safety margin, and hope for the best!

 

Well it would seem that's what some people do.

 

Now use your chosen diode with ISFM at 150 amps and try it. Considering that another manufacturer specs it at 75 amps. I guarantee that the two diodes are identical.

 

Zero K doesn't have to be achievable. It is irrelevant. That's why you'll notice, if you actually read it, my post said it was a theoretical current limit. Go back and read it. It hasn't been edited

 

And with that I completely give up. You've worn me out.

[Colin Smith]

“And with that I completely give up. You've worn me out.”

 

Me too……..Whilst I fully appreciate that the experts on here have raised and discussed the various issues with trying to deal with “spikes” and the potential for them to destroy LED lights, It has left me with the impression that there either isn’t a bomb-proof solution or at best only a theoretical one.

 

Just as a reminder the OP asked “do the more knowledgeable think this circuit (unique voltage suppression circuit on the LED light) is worthwhile or just not necessary” and I was after either confirmation as per the OP’s post or if there was something that could be plugged it to the circuit or attached to the potential source of the ‘spike’ to protect the LED’s. I must admit that whilst the ensuing debate about diodes and the like is possibly riveting for those who know and understand the subject, mere mortals such as myself try to understand but just don’t have the background knowledge, experience of expertise in the field to make sense of it all.

 

We all have our own areas of expertise mine is building race engines – I can build an engine that will compete with the best in the world but I can’t make it work without the magic black box and the correct ‘mapping’. For that I take it to a bloke who has a dyno, computers and doesn’t get out much, give it to him and a week or two later he gives it back to me with an invoice and a fantastic power curve.

 

That’s why we ask the questions - in the hope of enlightenment and that someone may say….you need one of these, get it from here and fit it like this. Alas, in this case that seems impossible.

 

I talked to a techy at a major manufacturer of pumps who also distributes high-end LED lights. The combination is fitted on sailing boats and super-yachts. They report no problems (or rampant warranty claims on the lights) and that their pumps have “a degree of protection” whatever that means. The LED lights they distribute are 8-30V DC and as far as I can tell are no different to stuff you can get from various suppliers and on eBay.

 

So, my solution is: I have quality pumps wired directly back to the DC link box next to the batteries via a dedicated switch panel. All the lights are on separate circuits via their own fuse board which is in turn wired directly back to the DC Link box. The other end of my solution is to reduce the cost of the LED lamps to the extent that if I do end up blowing some up, it won’t hurt too much financially. I can now purchase 8-30V DC LED G4 lamps for around $4 each and possibly less in future. This weekend, I will be fitting a couple of dozen, will switch them on, fire up the engine, flush the macerator toilet, run the shower pump, switch both the bilge pumps on and off, repeat several times and see what happens. If anyone is interested, I’ll report back!

 

In closing, I’d like to thank everyone who has posed on this thread. Your knowledge of electronics is staggering and I hope that what may be ‘simplistic’ questions from the likes of me won’t put you off from proffering a solution in future!

 

Colin

[WotEver]

This weekend, I will be fitting a couple of dozen, will switch them on, fire up the engine, flush the macerator toilet, run the shower pump, switch both the bilge pumps on and off, repeat several times and see what happens. If anyone is interested, I’ll report back!

Hi Colin - please do

 

As you said, a direct answer to the OP's question isn't simple because he asked "are the 'protected' ones worth the extra money?". No simple answer to that (see the thread about pet insurance).

 

Will they last longer? Probably.

 

Are they worth the difference? Probably. But possibly not.

 

Tony

[nicknorman]

Just as a reminder the OP asked “do the more knowledgeable think this circuit (unique voltage suppression circuit on the LED light) is worthwhile or just not necessary” and I was after either confirmation as per the OP’s post or if there was something that could be plugged it to the circuit or attached to the potential source of the ‘spike’ to protect the LED’s.

Its not unreasonable for you to want a black and white answer, trouble is there are so many unknown factors, including the way the circuits are wired, what devices are present to create transients, and the tolerance of the LEDs which varies with manufacturer and model. The type of damage transients can do to a semiconductor can be slow and accumulative, therefore I am not sure that your proposal to switch everthing on and off will prove much. If the LEDs blow, you have big problem!

 

Whilst there is no practical perfect solution to removing transients, their magnitude can be significantly reduced by using unidirectional transient suppression diodes (Traszorb, Transil etc being the manufacturers names for such things). Therefore I would suggest that you fit such a device to each circuit, at the first light in the cluster if there are several. Its wired across the supply and it must be fitted the correct way round. Cut the leads down so they are as short as possible (ie the device is as close to the wiring as possible. Be aware that with this solution, if you reverse connect the supply you will effectively create a short circuit which will blow the fuse and may blow the diode. The cost of these devices is in the order of 25p each, you can get them from Radiospares amongst other sources. I would choose a device with a standoff voltage of at least 16v (you would need to check the max voltage any charging system you have could attain, then add a margin).

 

If reverse polarity protection is important to you, go for Gibbo's solution but the component count goes up to 3 and you would really need some sort of component board (veroboard etc) to create a satisfactory installation.

 

If you wanted to conduct some research, how about fitting a diode to half of the circuits and not to the other half, then see if there is any difference in the life of the bulbs?

Edited May 22, 2010 by nicknorman

[nb Innisfree]

In closing, I’d like to thank everyone who has posed on this thread. Your knowledge of electronics is staggering and I hope that what may be ‘simplistic’ questions from the likes of me won’t put you off from proffering a solution in future!

 

Colin

 

[Colin Smith]

In closing, I’d like to thank everyone who has posed on this thread. Your knowledge of electronics is staggering and I hope that what may be ‘simplistic’ questions from the likes of me won’t put you off from proffering a solution in future!

 

 

Ooops..........I meant to type "posted" ......

 

Colin

[Colin Smith]

Its not unreasonable for you to want a black and white answer, trouble is there are so many unknown factors, including the way the circuits are wired, what devices are present to create transients, and the tolerance of the LEDs which varies with manufacturer and model. The type of damage transients can do to a semiconductor can be slow and accumulative, therefore I am not sure that your proposal to switch everthing on and off will prove much. If the LEDs blow, you have big problem!

 

Whilst there is no practical perfect solution to removing transients, their magnitude can be significantly reduced by using unidirectional transient suppression diodes (Traszorb, Transil etc being the manufacturers names for such things). Therefore I would suggest that you fit such a device to each circuit, at the first light in the cluster if there are several. Its wired across the supply and it must be fitted the correct way round. Cut the leads down so they are as short as possible (ie the device is as close to the wiring as possible. Be aware that with this solution, if you reverse connect the supply you will effectively create a short circuit which will blow the fuse and may blow the diode. The cost of these devices is in the order of 25p each, you can get them from Radiospares amongst other sources. I would choose a device with a standoff voltage of at least 16v (you would need to check the max voltage any charging system you have could attain, then add a margin).

 

If reverse polarity protection is important to you, go for Gibbo's solution but the component count goes up to 3 and you would really need some sort of component board (veroboard etc) to create a satisfactory installation.

 

If you wanted to conduct some research, how about fitting a diode to half of the circuits and not to the other half, then see if there is any difference in the life of the bulbs?

 

Hi Nick,

 

Thank you....that does help!! From your comments I understand that the damage could be accumulative so my switch-flicking may not reveal anything for months or years!! Using a transient suppression diode would reduce the potential risk. I’m going back to my supplier to see if they could include such a device and the effect that has on the price.

 

Failing that, I can use a soldering iron and your explanation of what/where to fit I understand – thank you.

 

Given that there is no immediate indication of LED’s being damaged (blowing up!) it’s going to be some time before I’ll know the reality – I will try different things but I may well be posting back in several months/years with my results and conclusions!! I guess that the thing to do would be to get the cost down to an acceptable level and add in some basic ‘protection’. I think getting the cost down as I have makes the ‘risk’ more acceptable and if they last more than a year or so, then it may be that they just become another consumable item.

 

Colin

[nicknorman]

Failing that, I can use a soldering iron and your explanation of what/where to fit I understand – thank you.

I kind of imagined you could fit them across a chocolate block connector near the light fitting, ie no soldering required!

[Gibbo]

Mr Nick

 

This isn't really related to boats because usually all the loads are connected to a different battery than the starter motor but I was working on something closely related earlier today for single battery installations.....

 

Work out what happens to the battery voltage in the case of a stuck/stalled starter motor.

 

I was rather shocked initially.

[Nickhlx]

Mr Nick

 

This isn't really related to boats because usually all the loads are connected to a different battery than the starter motor but I was working on something closely related earlier today for single battery installations.....

 

Work out what happens to the battery voltage in the case of a stuck/stalled starter motor.

 

I was rather shocked initially.

 

.... sounds "interesting" - any more details you can divulge ( in case others can learn from it) ?

 

Nick ( another one)

[nicknorman]

Mr Nick

 

This isn't really related to boats because usually all the loads are connected to a different battery than the starter motor but I was working on something closely related earlier today for single battery installations.....

 

Work out what happens to the battery voltage in the case of a stuck/stalled starter motor.

 

Stalled starter motor = no back emf = very high current drain, probably >1000A depending on wiring etc therefore depending on battery internal resistance, voltage will drop significantly. That bit I suspect is easy, what would be more interesting is what happens when you release the starter button. Or worse, when the starter solenoid starts cycling due to low voltage. Lots of energy stored in starter motor's magnetic field has to go somewhere, and of course its dissipated through the system as some pretty massive transients. But if its as simple as that you probably wouldn't have bothered posting, so tell us more...

 

I was rather shocked initially.

 

Didn't anyone mention its best not to put your fingers on the terminals with a live system?

Edited May 23, 2010 by nicknorman

[Gibbo]

Stalled starter motor = no back emf = very high current drain, probably >1000A depending on wiring etc therefore depending on battery internal resistance, voltage will drop significantly. That bit I suspect is easy, what would be more interesting is what happens when you release the starter button. Or worse, when the starter solenoid starts cycling due to low voltage. Lots of energy stored in starter motor's magnetic field has to go somewhere, and of course its dissipated through the system as some pretty massive transients. But if its as simple as that you probably wouldn't have bothered posting, so tell us more...

 

You're on the right lines.

 

When a runnning starter motor is switched off the resultant voltage spike (if any - usually there won't actually be any from the motor itself) will be positive.

 

But what about a stuck motor?

[nicknorman]

You're on the right lines.

 

When a runnning starter motor is switched off the resultant voltage spike (if any - usually there won't actually be any from the motor itself) will be positive.

 

But what about a stuck motor?

Tricky to answer precisely without knowing the exact topography (and even if I did, extensive modelling would be required which is beyond me!). The stalled armature becomes just a big inductor, so when current is interrupted the winding generates an emf so as to try to preserve the current. (assuming -ve ground system) the grounded end will go more -ve and the disconneced solenoid end will go more +ve, so with arcing on the solenoid contacts I would expect to see +ve spike, with -ve spike on the ground line. However it could all be complicated by the field windings (unless its a permanent magnet motor), the inductance of the solenoid (though pretty small energy store compared to the motor), the fact that the motor will kick back mechanically, and even possibly effects due to the magnetic saturation of the armature core.

 

So I think you will have to put us out of our misery and tell us what you saw!

[Gibbo]

Tricky to answer precisely without knowing the exact topography (and even if I did, extensive modelling would be required which is beyond me!). The stalled armature becomes just a big inductor, so when current is interrupted the winding generates an emf so as to try to preserve the current. (assuming -ve ground system) the grounded end will go more -ve and the disconneced solenoid end will go more +ve,

 

Exactly the wrong way round.

 

In order for the current to continue, the polarity on the motor terminals must reverse. The motor is now a source of EMF not a load connected to a source of EMF so internally the current is the other way round compared to the polarity of the terminals.

 

This is, of course, obvious and is the way any inductor operates but I'd never previously considered a motor as being stalled and therefore just an inductor.

 

This reverse source of EMF has the current capability behind it of equal magnitude to the stalled current.

 

I now realise why so many idiot diodes blow for no apparent reason on large vehicles

[nicknorman]

Exactly the wrong way round.

You are exactly right! Serves me right for replying after a quick one down t'pub on a sunny Sunday lunchtime! Back to reading "Inductors for Dummies" for me!

 

However

This reverse source of EMF has the current capability behind it of equal magnitude to the stalled current.

is not necessarily true. The "current capability" comes from the collapsing magnetic field, but iron-based cores (eg in the armature body) have limited capability for creating magnetic field - above a certain current, the core will saturate ie there is no increase in magnetic field for an increase in current. Therefore any current in excess of the saturation current will not be stored as energy, therefore any transient created will be no(t significantly) bigger than a max value. Whether the core of a starter motor goes into saturation when stalled I don't know, but I would have thought that the designers would only give it enough iron to not reach saturation during normal use - if it doesn't go into saturation when stalled its over-engineered and unnecessarily heavy and costly.

This is perhaps a good thing since if the core did not saturate, the transients would be worse!

 

Moral: Fit bigger idiot diodes, something has to absorb the energy!

 

As you will see from my profile, I am now a pilot and its standard aviation practice to switch on avionics etc only after engine start, esp on piston engined aircraft. You can get away with leaving the avionics on for many times, but if you do eventually something will fail prematurely (ie the damage tends to accumulate slowly) and that is with kit designed for the rigours of aircraft (you think a stalled starter motor is bad, try being struck by lightning!)

Edited May 23, 2010 by nicknorman

[Gibbo]

However

 

is not necessarily true. The "current capability" comes from the collapsing magnetic field, but iron-based cores (eg in the armature body) have limited capability for creating magnetic field - above a certain current, the core will saturate ie there is no increase in magnetic field for an increase in current. Therefore any current in excess of the saturation current will not be stored as energy, therefore any transient created will be no(t significantly) bigger than a max value. Whether the core of a starter motor goes into saturation when stalled I don't know, but I would have thought that the designers would only give it enough iron to not reach saturation during normal use - if it doesn't go into saturation when stalled its over-engineered and unnecessarily heavy and costly.

This is perhaps a good thing since if the core did not saturate, the transients would be worse!

 

I had to ponder this one long and hard.

 

These motors are either series wound, or compound wound and therefore, when the motor is stalled, it is effectively an air gapped inductor. Air gapped iinductors are specifically used because A. they don't get anywhere near saturation for the same current and B. they can store ridiculous amounts of energy because it's stored in the air gap which is somewhat difficult to saturate. Adding an air gap is the most common way of increasing the storage capacity of a given core in a flyback transformer. It is also the most common method used to reduce saturation of the magnetics. This fact doesn't affect normal running of the motor because when it's running as motor it is no longer an air gapped inductor.

 

I believe, therefore, that the back EMF current capability will indeed be the same as the stalled current. But I'm not 100% certain.

 

Moral: Fit bigger idiot diodes, something has to absorb the energy!

 

A bank of these might stand a chance...

 

 

As you will see from my profile, I am now a pilot and its standard aviation practice to switch on avionics etc only after engine start, esp on piston engined aircraft. You can get away with leaving the avionics on for many times, but if you do eventually something will fail prematurely (ie the damage tends to accumulate slowly) and that is with kit designed for the rigours of aircraft (you think a stalled starter motor is bad, try being struck by lightning!)

 

I really wonder whether that is the result of some hard leaned lessons some time in the past?

[nicknorman]

I am no expert on electromagentism nor starter motors, but I offer this: The point of an air gap in an inductor is to reduce the magnetic field strength in the core for a given current. This, as we mentioned, is to prevent saturation. But that is useful only in a transformer etc. In an electromagnet, surely there is no point in having a mechanism to reduce the magnetism and/or require a larger current to achieve the same magnetism - in an electromagnet you would normally want as much magnetism for as little current as possible. The only way to increase the max possible magnetic field strength for a given topology is to use a more advanced core material.

 

But the question is really: Is the overall effect of a field coil and armature coil in close proximity that they become one inductor with an airgap, or is it just two inductors without air gaps in close proximity to each other. Since the field directions are opposite, does the field from one help to reduce the field in the other? (thereby reducing the stored energy?). I dunno!

 

However it would not be hard to try - eg lock a starter motor, feed it gradually increasing AC voltage (so that the inductance is the limiting factor for current) and monitor the current - if the voltage to current relationship starts to show rapidly rising current for not much increase in voltage, the cores are saturating.

 

If that test can't be done, (due to lack of suitable power source) the overall inductance of the motor could be determined by measuring the voltage: current relationship at known frequency (no need for lots of power). The resistance of the windings could be measured with a meter and that allowed for if the impedance at the test frequency was not far away from the resistance. Knowing the resistance and the overall inductance, the stored energy in the motor could be calculated, and of course its this energy that is released back into the system when the stalled motor is turned off (assuming no saturation). Its a project for you on a rainy day!

[nicknorman]

Had a chat with someone from Bedazzled at Crick last weekend - they fit a parallel transient suppressor diode and a self-resetting thermal fuse to their led lights. The former has been discussed at length on this thread(!) whilst the latter it seems is to protect from a faulty light drawing excessive current that might be within the fuse rating for the entire lighting circuit, but nevertheless sufficient to cause overheating or worse when it all goes into one light.

 

These devices are connected in series and are normally low resistance (1/2 ohm or so), they go very high resistance when the threshold current is exceeded, resetting themselves to normal low resistance when they cool down after the fault is removed. Not sure how necessary they are (ie how likely a device failing short-circuit and overheating to perhaps cause a fire) but for around 50p each they are perhaps worth it for peace of mind.

 

Anyway the transient diode plus the fuse thing could be bought for £1 or so, so there should not be a great premium for the Bedazzled devices over other retailers, though they should get credit for thinking about it! Another reseller I spoke to said that he recommended use of a buck regulator to fix not only the problem of the higher voltage with engine running, but also that of the transients. Mmmmh!

 

As a general point, saw some some boats with fantastic led lights that were nearly indistinguishable from halogen, save for the lack of heat. They certainly have come a long way from the harsh cold white lights of a year or two ago!

[Gibbo]

Had a chat with someone from Bedazzled at Crick last weekend - they fit a parallel transient suppressor diode and a self-resetting thermal fuse to their led lights

 

Did you actually read post #1 in the thread?

 

I have recently bought several led lights from 2 suppliers ,one company supplies the lights with quote" there own unique voltage suppresion circuit " which consists of a 300ma self resetting fuse & a transient voltage suppressor wired across.....

 

[Nickhlx]

Well that's the major manufacturers in Japan out of business overnight then !!

( where can I buy the self-resetting 300mA fuses ?)

 

Nick

 

[Gibbo]

Google "polyfuse" (one of the common tradenames).

[Nickhlx]

Google "polyfuse" (one of the common tradenames).

 

 

I didn't think that a "polyfuse" could react fast enough or handle the voltages / currents involved, and were more suited to e.g. protecting small battery packs from abuse .....

 

Nick

[nicknorman]

Did you actually read post #1 in the thread?

 

Yes

Edited May 31, 2010 by nicknorman

[Gibbo]

I didn't think that a "polyfuse" could react fast enough or handle the voltages / currents involved, and were more suited to e.g. protecting small battery packs from abuse .....

 

Nick

 

They're faster than normal fuses. For voltage ratings you have to read the datasheets really carefully. Most are available at 30 to 40 volts.

[nicknorman]

I didn't think that a "polyfuse" could react fast enough or handle the voltages / currents involved, and were more suited to e.g. protecting small battery packs from abuse .....

 

Nick

 

They are quite slow - many seconds (depends on the excess current) but I think the general idea is to protect from a modest overcurrent that would not otherwise blow the circuit's fuse but could over time cause major localised overheating. If you have a circuit with a number of lamps, and rather than the power being evenly distributed between the lamps, a fault causes nearly all the available power to go to just one lamp, it could overheat dangerously. With each lamp being protected by the polyfuse, that device would trip before the heat became sufficient to cause a fire. Or that is the hope...

 

Edited to disagree with Gibbo - they are pretty slow since their thermal capacity is much higher than a thin bit of fuse wire. With a substantial over-current a fuse will melt within a second or so (depends on type) whereas the polyfuse will take maybe 10 to 20 seconds to heat up above the threshold temperature

Edited May 31, 2010 by nicknorman