trailor alarm wiring

hi, I have an alarm system on board a trailor that is powered by an on-board battery. I have it installed and working fine but I have not tapped into the exterior lights yet. I need to know how to determine what size diode I should use and where to locate it in relation to the fuse (before or after) I dont know for sure if its actually needed in this case but I dont want to run into problems when the trailor wiring is plugged into the tow vehicle (seperate 12vdc source) does anyone know what kind of problematic issues I might have when they are connected (tow vehicle and trailor) and each has its own alarm system and power source? both alarm systems are the same type. autopage RF425lcd thanks

I could really use some experienced input on this so Im bumping it back to the first page. thanks again

I am assuming you are OR-ing the lights? (ie, on for alarm or from light switch). You therefore need a diode in EACH feed (to stop either feed feeding the other). The diode should be rated to carry the lamp current - eg, (total Watts)/12 - eg 2x3W = 6W/12V = 0.5A => IN4004 1A (400V) diode; 2x21W = 42/12 = 3.5A => a 5A diode. Fuses should be places as close as possible to sources (battery) before any devices/components.

hi oldspark, yes, for alarm flash parking/running lights so its best to place them at each alarm control units light flash output wire I assume. now, to determine the amperage..I have alot of lights because when the trailor is connecter to the tow vehicle all the running lights from both must be accounted for since in that case either alram will flash all the running lights on both tow and trailor I think. is it OK to use a 5a diode in a circut that only has 1a current, let me rephase that.. will 5a diodes work for all currents under 5a? in otherwords, are the larger diodes OK for the smaller currents but not the opposite? Thanks oldspark, once again you have come through for me here. I really apreciate it. now I try harder to find more difficult questions ;-)

two12 wrote: now I try harder to find more difficult questions ;-)

I didn't see that it was you (I just answer; but rarely read!). People wonder why - with friends like you - I find enemies unchallenging! You are quire correct.... 5A handles 1A etc. (Generally the same for any "simple" component. But not always - eg a 100A transistor may have troubles modulating/controlling a 1mA current.) Make sure your outputs handle the total currents. If currents get too high, you could have the output(s) control relays. Wiring depends on the batteries - if the trailer battery is always there, it could power the lights - ie, diodes from car & trailer controllers thru their diodes to a trailer mounted relay (switching trailer battery +12V to trailer lights). And (normally) parallel batteries should be avoided, but it's ok when charging. (You have probably seen my other posts regarding a charge-lamp controlled relay to connect the main alternator/battery to auxiliary batteries (much like some Fuel-Pump control circuits), else an overvoltage switch to do the same (eg - above 13.5V). As to difficult questions - I usually find few are difficult. Many are difficult to understand (ie, lack specifics), and many are difficult to explain (concisely!). The difficulty is writing so that people understand. The impossibility is making idiots try to understand! (As a colleague recently pointed out, I too have many replies that pose questions or "please explains" to previous posters that have no subsequent replies. They reckoned too many to account for mere forgetfulness or trivialities.)

oldspark wrote: Wiring depends on the batteries - if the trailer battery is always there, it could power the lights - ie, diodes from car & trailer controllers thru their diodes to a trailer mounted relay (switching trailer battery +12V to trailer lights).

hmmmm

oldspark wrote: And (normally) parallel batteries should be avoided, but it's ok when charging. (You have probably seen my other posts regarding a charge-lamp controlled relay to connect the main alternator/battery to auxiliary batteries (much like some Fuel-Pump control circuits), else an overvoltage switch to do the same (eg - above 13.5V).

I am trying to avoid any parallel issues here. I'll definately look into your other posts if they fit this topic. also regarding 12vdc parallel and isolation, currently Im trying to determin which of these two products are on the up and up regarding split-charging. mabey you can help if you dont mind some reading. it is an intresting subject. first the more simple one here: http://www.powerstream.com/battery-isolator.htm then a much more complex unit here: http://www.smartgauge.co.uk/smartbank.html this Co. has quite alot of info but without a proper background in this field I cant determin if it is snake oil or not. from one of their other pages: Split Charge Diodes are dated and do not work properly! http://www.smartgauge.co.uk/diodes.html also "I have heard that relay based split charge systems suffer from a serious problem with a dangerously high initial current surge measured in hundreds of amps"http://www.smartgauge.co.uk/nosurge2.html if you have some time for the reads, I'd love to hear what you make of all this.

oldspark wrote: As to difficult questions - I usually find few are difficult. Many are difficult to understand (ie, lack specifics), and many are difficult to explain (concisely!). The difficulty is writing so that people understand. The impossibility is making idiots try to understand! (As a colleague recently pointed out, I too have many replies that pose questions or "please explains" to previous posters that have no subsequent replies. They reckoned too many to account for mere forgetfulness or trivialities.)

HAhaha! just you wait Man.. Im still just getting warmed up! think I've found one expert here at least so that helps.. after the multiple 12vdc source quiz well move on to soloar powered senarios. I hope your good for it..

Ok - here we go..... Split charge systems - IMO = snake oil (as you put it). Reasons - to charge one before the other - bullsh! (Else, why?) To divide the charge - again, why? If the split charge is settable to suit a battery - eg, to current limit to an AGM/VRLA, or a small battery - then fine, but I have yet to see that featured. Hence the simplicity of a cheap relay (I use a 60A relay to connect my 2nd 55AH CCA 475A battery; the alternator is 70A - 100A (depending on procrastination and testing). An important issue is to fuse "both ends" - ie the +12V terminal of each battery or their interconnection. As to split charge diodes - see adding a second battery - page 2 for a split diode system. Although the next page shows a high/low voltage sensor, the simpler circuit I refer to is similar to: (the above (modified) diagram wit thanks to my poor victimised colleague.) The advantage of that system is its simple and (probably) cheaper relay, total isolation of the batteries when not charging but without the diode voltage losses and other complications of the split diode system. (And why Schottky diodes? Just any power diode surely?) A disadvantage is the need for a charge-lamp circuit that can drive a relay. But most alternators will. Older vehicles with electric fuel pumps often use the charge lamp circuit (only) to control the fuel pump relay. In such vehicles, the fuel-pump relay could power the Aux battery's relay. Otherwise an over-voltage sensor/switch that controls the relay is required. Now for solar panels.... You want to know that solar panels DO NOT contain any energy storage (aka batteries)? You want to know that it IS well & truly feasible to provide tracking to GAIN power (more than 3 degrees off-normal is usually 5% or more energy loss; soon rising to over 20% above 5 degrees etc)? You want to know the difference between a panel's "rated" output and its most likely "real" output? You want a regulator that's similar to my ~$20 kit (for 150W or 300W, maybe more)? You want to know why it is (generally) a joke using solar power in a gasoline powered car? Bring it on Baby. Bring it on!

oldspark wrote: Ok - here we go..... Split charge systems - IMO = snake oil (as you put it). Reasons - to charge one before the other - bullsh! (Else, why?) To divide the charge - again, why? If the split charge is settable to suit a battery - eg, to current limit to an AGM/VRLA, or a small battery - then fine, but I have yet to see that featured.

I think that is what the smartbank unit (second link in my previous post) does but I need to read about it again thats one reason I mentioned it. let me know whenever you have had time to scope it out. I may have to read it a few times before I get it. then there is also the morningstar sunsaver duo, its a solar charge controller specifically for use in dual isolated battery systems. a new controller and unique design, so far its the only one of its kind. it is programable and it may also work with other charging inputs instead of PV (solar panels) but by design it is a solar charge controller and therfore its expensive. I have a couple of these along with a regular controler

oldspark wrote: Hence the simplicity of a cheap relay (I use a 60A relay to connect my 2nd 55AH CCA 475A battery; the alternator is 70A - 100A (depending on procrastination and testing).

I like simplicity! but before I get way off topic.. please tell me how you (oldspark & other experts) would wire up this sytem: two autopage RF425LCD systems, one onboard the tow vehicle, one onboard the trailor. both have their own isolated power source. the issue is when they are linked by the parking/running light wirring while attached. I need them both to function as normal and independently of each other. how would the12volt experts do it?

oldspark wrote: Bring it on Baby. Bring it on!

Thats what Im talkin' bout right there! the12volt.. mabey this is the right place? or is oldspark the only expert here up for a real challange HAHaha! no worries oldspark.. Ive got lots to "bring on" here! Im starting with the relatively simple stuff. one thing at a time though because Ive got to absorb it before I can test it. Im not the12volt expert but with enough help it wont take me long. thanks

BTW my local radioshack didnt have 5a diodes in stock, is there a chance local autoparts houses stock these? if not, wheres a good place to obtain them in bulk online? thanks again.

Just an interim reply. You could try 2x3A diodes in parallel, though if one opens circuit, the other will fry (above 3A). Then again, the voltage drop will halve... (just kidding! They are NOT resistors!!) Else use 1A diodes with relays....? I probably won't look into those charge splitters until someone can explain WHY they are required. Battery (cell) equalisers no problems. But "parallel string" charge splitters? Why? (Except in the obvious cases where charge time is insufficient to recoup the main battery, but how many systems charge for a few minutes only? And if recharge power is that short, adding an extra power drain is not helping.) But more later.... (Off to choose a 10" lappy or netbook for someone. Urgghhh! And I was going to simplify someone's diode & relay switching for LEDs.) Keep coming. You keep cumming, and I might start too. (Enuff!!)