24V - 12V Converter Relay Switch (1 Viewer)

[CDN_Cruzer]

Can I use a Hella 87426 Relay to switch the power to my Converter? It is a ICT 30Amp model so it should only draw 15amps in 24V and the Relay says it can handle 20amps.

If I cannot use the hella relay what relay should I use? I do not want to use a switch as I know I will forget to switch it!

I have done some searches but can't find this info.

 

[eleblanc]

What ever relay you use don't hook it up so that it feeds the converter, instead feed the relay from the converter to feed accessories. In other words hook the relay after the converter and use ignition current from the fuse box to switch on and off the relay. So it allows you to have get current from relay when your ignition is at accessories or on position depending on how you hook it up.

If you know that the accessories you use will not draw more then 20 amp then use that 20 amp relay.

I personnaly would use a higher rated relay, like i did, a 50 amp Bosch relay. Search my name and Relay and you should find out about my setup.

 

[Ron R]

What ever relay you use don't hook it up so that it feeds the converter, instead feed the relay from the converter to feed accessories.

What is your reasoning behind this setup? This way the convertor will still draw from the batteries and there is nothing too feed to. In my opinion there is no need to have the convertor connected if there are no accessories needing juice.

This way the convertor will still draw some (100?-300?) mA from the batteries and drain them when not driven for prolonged time. Especially in wintertime, the batteries can get drained enough in 2-3 weeks so that starting is impossible.
I had that kind of setup (to feed my alarm and radio/player memory) and had lots of problems.

I think - no, I'm sure - it's better to put the relay in front of the convertor and have it switched by either "IGN" or "ACC".

If you know that the accessories you use will not draw more then 20 amp then use that 20 amp relay.

I personnaly would use a higher rated relay, like i did, a 50 amp Bosch relay. Search my name and Relay and you should find out about my setup.

If the convertor is rated for 30A/12V and you put the relay in front of it, your 20 A relay will do the job, but a higher rated would be better. This because the start-up current will be fairly high. Go for at least 30 A but as Eleblanc says, go for 50 A or so if you need redundancy. (or keep a 20 A spare)

 

[danhr]

Ron has a valid point.

I would suggest you use two relays rated 20amp (the one you have), in parallel to the battery. Thus 20+20=40. That is only if you cannot get a relays with higher ratings. Use qulaity wires (the ones that have low capacitance).

 

[CDN_Cruzer]

thanks for the help. I want this done right so I am going to try to find that 50Amp Bosch Relay.

Eric Where abouts did u find it?


I would perfer to put it in front of the converter as my truck sometimes sits in the cold for a week.

 

[eleblanc]

My reasoning is if you want more then one relay like my setup you wil need to install them after the converter. Since my converter has full time current it can feed radio memory. All the rest of the 12v accessories are hook to 2x Bosch relay connected after the converter. Giving me 2 sources of 12V, One when the ignition is at accessories and one when it is at the ignition on position. Putting relay before the converter would not allow you to do this.

For exemple i have my air locker solenoid hook to the accessories position, so when i stop the truck in the trail they don't disengage. And the pressure switch of the compressor is on the On position so that the compressor only runs when the truck is at on position thus running.


picture 106.jpg

 

[eleblanc]

thanks for the help. I want this done right so I am going to try to find that 50Amp Bosch Relay.

Eric Where abouts did u find it?


I would perfer to put it in front of the converter as my truck sometimes sits in the cold for a week.

I will look through my pictures for the bosch number and post back.

If you prefer in front then simply because the truck sits in the cold for weeks, simply use a 30 amp rated switch. When you park the truck close it.

You use a relay because you want to use a external power source to activate or desactivate load power coming out of the converter. Just like i did with ignition current.

Unless you wish the current going to the converter to be syncronize with ignition then you need a relay, otherwise get a simple switch properly rated. In my case i have a kill switch that closes the ground from the battery to the frame, thus shutting down any possible electrical power source (for winter storing)

 

[eleblanc]

Here is the relay i use.

 

[canadianmedic2]

I use the same one, it's a good little relay. A little on the pricey side, I think I paid around $50bucks.

 

[Freewheel]

I've got a 4 dollar 12v relay from a bulk electronic component store on my 20 amp samlex converter. I put it on there as an emergency measure when my rather expensive Bosch 24volt 30amp relay stopped working one week after I installed it.

It's been running my stereo and 120v inverter for a year now with no issues.

YMMV

 

[danhr]

From my experience, if you supply 24V directly to a converter, it will drain out battery within a week (when not used for a week). Use it lightly, it takes about 2months (like use it two times a week, few miles).

In anycase, be it any converter (so long as it is not a switching converter), it draws atleast 0.27amps. That is equaly to two 10watts 24V bulbs (I compared it to brake lights).

Again, I was guided by Ron over this and he has a solution.

 

[eleblanc]

I've been using my setup for a year and a half. I never add a issue, and can be 2-3 weeks in between time i use my truck.

I just did had dead battery, Truck is stored for winter and i had forgot to turn the kill switch off. But i have a 24V GPS tracking device (since this summer) using full time current, so i was expecting this to happen. The cool thing about the gps device is if the 24V current is getting low it sends me a SMS on the cell, so i go back and start it up...But i now have shut the kill switch.

I cannot explain to my self how a converter can draw current if the output is not connected to anything. I agree tho if it feed radio and other device pulling small amount of current, battery will go dead, how fast i have no idea. But a converter by himself pulling current? someone has to explain me this...

My truck is used ONLY for wheeling, so in the summer it is some time not used for 2-3 weeks and i never had issue and my converter is connected directly to the battery. Sometime and probably most of the time battery going dead are not even related to the converter but a evel tap in between batteries.

 

[danhr]

eleblanc:



It could be that you are using quality batteries. And perhaps, since my 4x4 alternator has a external cutout, it only charges to the required voltage when reved up.

I have been banging my head since long trying to find the cause of the drain. Eventually I traced it to the converter. The whole story is explained:

Battery, Alternator or its cutout? - IH8MUD.com Forum


The kill switch is a good idea but is good if you really do not want the truck for weeks.

And yes, even when there is no load, the draw remains in 0.2amp range. The reason being that a linear converter reduces 24 to 12 by dissipating heat (very inefficient). Now since say an IC like LM7812 (found in converters, if you hack one) has some quiescent current, which is low. BUT the transistor which boosts the current, located in front of LM7812 (generally speaking), is of higher rating and has a big quiescent current. While LM7812 might be rated 1amp of max load, a single transistor like 2N3055 is rated for 15amps max. And in a 6amp DC-DC 24-12 converter you will find 2 such transistors and one LM7812 (or its substitute). In a 10amp three transistor, 24amp seven transistor etc.

Be it 6amp, 10amp, 15amp 24amp (I have them all), idle draw (without any load) is above 0.2amps. Tested and verified by me. All of these converters were linear. If you have a switching converter, the story is different then.

Well, these are my views and I could be wrong.

 

[eleblanc]

eleblanc:



It could be that you are using quality batteries. And perhaps, since my 4x4 alternator has a external cutout, it only charges to the required voltage when reved up.

I have been banging my head since long trying to find the cause of the drain. Eventually I traced it to the converter. The whole story is explained:

Battery, Alternator or its cutout? - IH8MUD.com Forum


The kill switch is a good idea but is good if you really do not want the truck for weeks.

And yes, even when there is no load, the draw remains in 0.2amp range. The reason being that a linear converter reduces 24 to 12 by dissipating heat (very inefficient). Now since say an IC like LM7812 (found in converters, if you hack one) has some quiescent current, which is low. BUT the transistor which boosts the current, located in front of LM7812 (generally speaking), is of higher rating and has a big quiescent current. While LM7812 might be rated 1amp of max load, a single transistor like 2N3055 is rated for 15amps max. And in a 6amp DC-DC 24-12 converter you will find 2 such transistors and one LM7812 (or its substitute). In a 10amp three transistor, 24amp seven transistor etc.

Be it 6amp, 10amp, 15amp 24amp (I have them all), idle draw (without any load) is above 0.2amps. Tested and verified by me. All of these converters were linear. If you have a switching converter, the story is different then.

Well, these are my views and I could be wrong.

I have a ICT converter, since you are bringing this up i'll have to go check if it does draw current at the output. I expect it will since my radio is hooked on it.