led’s and car alarm

Yep - that looks ok. Include a quenching diode across the relay's coil/solenoid (85, 86) to prevent coil-generated spikes - hence protecting the alarm "input #3". Also known as spike suppression diode etc - it's just a "reverse biased" diode - say an IN4004 (400V 1A) diode or similar. (See info elsewhere - browse the excellent tuts here at 12volt.) I'm assuming input #3 can be used as an output. But the key issue is if it can only source or since 200mA. Hence your relay's coil must use under 200mA. Some relays state coil resistance but not current. Remember that V=IR so R=V/I, so 12V/200mA = 60 Ohm, or (say) 14.4V/200mA = 72 Ohm. (Normal ratings would be at 13.8V hence 13.8/0.2 = 69 Ohm.) In other words, your relay's coil should have a resistance of at least 72 Ohm. (Higher resistance means lower current, so <200mA means >~70Ohms.) Most common automotive relays are at least that should you should be ok. (I use JIDEC relays and they are ~68 Ohm or higher.) Other common relays (for electronic circuits) are usually 160-450 Ohms. So no problems - watch that coil current/resistance (ie, > ~70Ohm, or 12V at under 200mA). For the relay contact ratig, you are only using about 1 Amp. But 15A or 30A are the common and hence cheapest suitable relays. A mere SPST (on-off) will do, but an SPDT (chanegover contacts) is fine (just don't use 87a). The rest below is probably incidental.... The only other little bitty tiny incidental thing..... Does you diagram mean your are doing 4 LEDs without resistor per string? In that case I should point out the possibility of thermal runaway, but that is probably not a problem anyhow and it will only destroy the string it is in if it does occur. I get the impression that most "clever" people use (say) 4 LEDs in series without series resistors because it just ain't worth the hassle of the resistors, and it's 20% less soldering or strings etc, and they are prepared to replace the string(s) should problems ever occur. [I have 2 links somewhere - one points out that strings tend to be self stabilising because the other LEDs limit the current etc; the other shows how people will argue despite them having their electrical basics very wrong (Ohm's Law), and they never do a simple example/analysis of a string of LEDs (despite linking to complex data and info themselves).] If using resistors, I should still point out thermal runaway, and that for high-voltage strings (where the supply voltage is much higher than the series LEDs), only a constant-current element per string will prevent it, though a resistor does provide some stabilisation....

would I be safer to use resistors to make sure the LED's do not get an over voltage, I would prefer them to last a long time then having to replace them all the time.Viper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed

what resistor would you hook to each 4 led chain to keep it from damaging them?Viper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed

Probably no resistor for 4 LEDs. But what is the max voltage the string could see? And what is the max voltage or rather, current - each LED can tolerate?    You may have to decide yourself on the risk. I get the impression thermal runaway is generally not a problem for low voltage situations - ie, 15V etc. For a short overview of LED thermal runaway, see What's the deal with LEDs wired in series or parallel? What about "current hogging" and "thermal runaway"?. For more detail, see Avoiding thermal runaway when driving multiple LED strings To see how some beg to differ and then beg release - aka hang themselves wrt LED resistor & thermal runaway arguments - see mp3car's Changing cold cathode backlighting to LEDs (+auto brightness control) The best thing in the latter is the LED spec in post #59 - ie, the " nice LED" pdf link - that gives some nice Vf and current characteristics.

I think i will do what I did in my setup picture, 4 per series, and then parallel the series ones together, but I will add a 33ohm resistor just to help a bit if the voltage on the battery starts to go above 13v, do I put the resistors on the negative side of each series string, or the positive side going into each set of series?Viper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed

Hey, I was wondering, could I use this switch on the led's Switch Link, I want to hook up the door on switch to the led's and have this switch between them. So it would be a door switch and a auxilary output to the relay, same input on relay, and diodes on each auxilary and door wire to keep current from flowing back, and then this switch would go between the door and relay wires, and another switch between aux output and relay wires, that way I can make it so the door do not turn on the led's and the remote could make it so I could turn off the auxialy output from turning on led's?Viper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed

So you will use 2 20W or one 40W 33Ohm resistor? I suspect that has more effect as a heater than helping limit the voltage! [quick calcs- 39 leds in 9 strings of 20mA each = 180mA x 33R = 5.94 = 6 volt drop across the resistor, or 12V if for all 18 strings.... if 6V, 15v-6v = 9v/4 = 2.25V per LED if it were 33R per 20mA string = .66V across resistor => string V (presumably) is 4x3.3+.66 = 13.86V. if 30mA = 3.5V (from mp3LinkData) then Vs=4x3.5+.03x33 = 15V, so 15V via 33 Ohms in each string is LED current of 30mA; voltage increases 8%, resistor-V increases 33% as does LED-current, led-V increases 6%.] Yeah - need to compare to non-R version.... Resistors like switches can go anywhere - it doesn't matter. IE - you can switch +ve or ground. Within a string, a resistor can go anywhere - ie, -R-L1-L2-L3- or -L1-R-L2-L3- or L3-L1-L2-L4-R- If the alarm like the door-switch is grounding, you might be able to join them together to ground the relay solenoid (#85) with the other end {#86} to +12V. But then both are grounded together - ie, the alarm turns on door lights etc, so it needs some thought. What else is connected t the door switch etc? A switch between #86 & +12V can be master of switch. Another ground switch connected to #85 can be a manual on. There are lots of ways depending on how things are wires etc.

I am going to do series of 4, each led is 3.1 volts, so 13 volt car battery - 3.1*4 = .6 voltage left, then .6/.02, because of a 20ma draw, so it ends up 30ohms, so I got 33 ohm resistors, and will do sereis of 4 with a resistor on the positive side of each set, and will do a total of 72 leds with 18 parallel groupsViper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed

A 12V battery is rarely 13v. A normal range is from flat 11.6 to full 12.6 or 12.7. If higher, it's usually due to surface charge that they have after charging - typically up to about 13.6V. And not that your engine will be running whilst disarming the alarm etc, but the battery is usually from 13.8V to 14.4V - ie, the alternator voltage, where 14.4 is the typical maximum long-term battey charging voltage.    Some vehicles may charge at up to 16V just after cranking. Some batteries (Optima, Odyssey) may allow above 15V. I'm pointing this out in case you are not aware of normal voltage ranges. I would expect that a full battery that hasn't been charged for a while etc - eg, a rested vehicle with an alarm system after a few hours - would have a battery voltage of about 12.6V. (3x4.1 = 12.4V) Not that the resistor value will make much difference - it is not that critical - use 27 or 33 Ohm (not 30) - it is 0.02 volt difference per Ohm (20mA x 1R = 20mV).

I only did that as a voltage because it was a bit high, so to make sure the leds do not get overpowered, what is the lowest voltage a led can work without the power going out? cause if you get voltage drops from lets say a kicker 1500.1 amp pulling easily 100 amps, would that cause the leds to go out?Viper 5902 - Ordered

Kicker Dual CVX 15's - Installed

Kicker ZX 1500.1 Amp - Installed