3 vs 4 Post Contactors

[ctbecker]

I recently got a continuous duty contactor from B&C. It came with 4 posts. All the drawings I've seen show contactors having 2 line posts and a ground post. Could someone explain the difference and how the 4 post contactors are wired?

[Mike S]

They sell a couple of four post contactors------and this one doesnt come with directions, you have to get it from the web site.

http://www.bandcspecialty.com/S702Wire.jpg

Be careful, it is easy to kill the internal diode if you hook it up wrong.

BTDT

[gmcjetpilot]

Guys the picture above is for a starter relay (intermittent duty) not continuous duty contactor (ie master or Bat relay).


Master (Bat) Contactor: Besides the two BIG terminals which is common on all contactor's (relays), battery in & out, you have either one or two small terminals for the coil. If there's one small terminal, it's wired to the master switch to ground. A "catch diode" goes from the single small terminal to the large POS terminal on the contactor, battery side. The diode strip goes towards to large POS terminal. See three terminal pic below. The pos side of the coil is internally wired.

With the Four terminal version, the second small terminal gets and external "jumper" to the positive BIG terminal on the battery side of the relay with a wire (diode not needed). The diode now goes between the two small terminals, with the stripe end towards the positive side of the coil (the terminal with the jumper - see pic below). The difference between the one/two small terminal versions is the 4 terminal version has an external jumper to the pos side of the coil, the 3-terminal version is internally jumped.

Three post Master Contactor (continuous) CLICK


Four post Master Contactor (continuous) CLICK


Starter Contactor: Is similar in terminals to the master, in that they come in three or four post versions (one/two small terminals), but when you have the forth post, you just don't use it. There is no extra jumper. The small terminal labeled "S" is for starter switch. It is always used, and activation is with a POSITIVE momentary fused switch. The other side of the coil is grounded. The small 4th post you don't use is labeled "I" for ignition. On some cars this goes to the Ignition coil. In previous text some one says its for starter engaged light. It could be used for that. If you want a starter engaged light and don't have that 4th "I" terminal, you can go off the big terminal on the starter side. The 4th small terminal (if installed) is just internally tied together with the big output terminal when the relay is closed/activated. The "catch diode" is wired as shown above, from the "S" terminal to grounded, usually mount bracket bolt.

Here's a great gouge from our friends at Vertical Power that explains relays with pictures. By the way, ignore PAGE 5. That's probably your relay but you don't need all those diodes shown. Just one diode as shown above will work great. Picture on page 5 is for a cross-tie application, which justifies all the diodes I was told. http://www.verticalpower.com/docs/Contactor_Wiring.pdf

Side notes: Typically the master is all metal (silver finish) and starter is a dark composite plastic housing. Note in the one picture above, the master is mounted pointy/cap end up and the starter metal cap (terminals) down. (This avoids inadvertent activation from pos vertical G-force overcoming spring.) With the starter relay B&C sells, it does not matter (it mounted horizontally). However personally the horizontal mount starter relay B&C sells does not fit as nice as the ones Van's sells (see pic above). B&C's solenoids are not superior in quality or function to the ones Van sells; they just have different configurations. There all stout, simple, heavy duty industrial relays.

[az_gila]

Simpler pictures of the internal wiring options for the contactors are available from the Cole-Hersee web site...
The guys that make the parts...

http://www.colehersee.com/pdf/H-Relays.pdf

Note that while 4 post contactor can be wired for a starter as George says above, it can also be used with all for posts connected by an external connection between two posts.

We also classify them as continuous and intermittent, but they are all continuous duty (at 85 Amps) according to the data sheets. For the higher current starter application, the 200 Amp model is best, which is the 4 post 24143 model.

gil A

[gmcjetpilot]

Originally Posted by az_gila

Simpler pictures of the internal wiring options for the contactors are available from the Cole-Hersee web site...
The guys that make the parts...

http://www.colehersee.com/pdf/H-Relays.pdf

Note that while 4 post contactor can be wired for a starter as George says above, it can also be used with all for posts connected by an external connection between two posts.

We also classify them as continuous and intermittent, but they are all continuous duty (at 85 Amps) according to the data sheets. For the higher current starter application, the 200 Amp model is best, which is the 4 post 24143 model.

gil A

Great stuff as usual Gil. A few questions?

Did you notice the latching continuous contactor? That would save 0.75 amps over the standard contatactor, which takes current to stay on. Cost? Weight? What do folks think of using a latching master? It would save the current and not get hot. I see if your battery drained it would be latched on. Is that a problem? As soon as you jump the battery with a charger you could cycle (latch) back to off.

I noticed a lot of intermediate "duty times" with times like 10 secs on, 20 MINUTES OFF! Of course that's at max 750amps. Our starters draw a max of about 350 amps or less, but still it's a good heads up. Guys fighting a hard start (heat soaked, flooded what ever), need to let the contactor / starter cool between attempts. I think Sky-Tec has a 10sec on, 20 sec cool cycle a few times. After 6 attemps its 30 min cool. But the starter relay (on firewall) may be the limiting factor.

[w1curtis]

Originally Posted by gmcjetpilot

..
Did you notice the latching continuous contactor? That would save 0.75 amps over the standard contatactor, which takes current to stay on. Cost? Weight? What do folks think of using a latching master? It would save the current and not get hot. I see if your battery drained it would be latched on. Is that a problem? As soon as you jump the battery with a charger you could cycle (latch) back to off.....

George, I saw this and though about it's use also. Not specifically to save amps, just as an alternative. If your battery drained and it latch ON, then it would be OFF anyhow so no problem there. In addition to cost and the mentioned items, I'd also be interested in failure modes. One I can think of is a possible transient voltage "tripping" it OFF unintentionally.

[Rick S.]

I notice that these relays getting pretty hot during operation. I seen this referenced before as anywhere from warm to hot....I put mine in the"hot" catagory.

Any input regarding the heat generated by the relay while in operation? I have one to control my avionics master power.

[Steve Sampson]

George, and others, The 4th post on the starter contactor is quite useful if you are using the Skytec starter unit which has its own contactor. If you take the jumper off the Skytec, and connect the 4th post with its own circuit to the small terminal on the Skytec, and the power terminals together also, when you activate the starter contactor the 4th post causes the Skytec solenoid to move and the big terminal switches the power forward to the Skytec.. Still with me? If so you are probably wondering why bother. Now the good bit is coming.

When you open the starter contactor the voltage on the 4th post drops so the Skytec solenoid retracts. If you read RVator, in the past, there were cases of the engine firing, and before the solenoid retracts the alternator acting as a generator, current flowing through the link to the solenoid and it staying engaged. Ouch!

Now I have never experienced that, but you will find it reported as a problem by VANS in RVator.

Having got that far though you might start wondering (as I am) if you still want a starter contactor on the firewall since you have one on the starter unit. I am considering ditching the starter contactor and using a simple relay just to switch on the power to pull the solenoid in. The relay is because you have to switch 30 amps which is required initially to pull the solenoid. Once you have wired it this way, you might as well send the alternator power back down the starter cable also! Saves a bit more weight. I am still thinking about it, but would welcome comments....if you have followed this far.

Oh, and to make it safe I think I would put a 40amp ANL between the alternator and outer end of the starter cable, and a 300? amp ANL right by the master contactor where the power heads out to the starter. As I said, still thinking.

[gmcjetpilot]

Originally Posted by w1curtis

George, I saw this and though about it's use also. Not specifically to save amps, just as an alternative. If your battery drained and it latch ON, then it would be OFF anyhow so no problem there. In addition to cost and the mentioned items, I'd also be interested in failure modes. One I can think of is a possible transient voltage "tripping" it OFF unintentionally.

The big problem is its an odd ball. With a normal relay you have a ON and OFF switch. Switch on switch to on the relay is on or closed. Switch off, the relay opens or is off. If you lose power the relay goes to its normal OPEN or off fail safe position. You really don't know if its on or off by the switch. Relay position is determined if you have power or not. That means you need battery power to know the position and/or activate it.

The latching needs a momentary switch, normally open. Hit the button once it FLIPS and latches either open or closed. Hit the button again it FLIPS and latches the opposite of the previous open or closed position, like a click ball point pen. You can NOT use a normal SPST On/Off toggle switch with the latching relay. Leaving the coil "hot" burn it out in less than a minute or two. The coil is designed for momentary power only, to flip the relay closed or open. Once you flip the relay, you need to remove the power to the coil. That is ODD switch operation from what we are use to. Is it a problem?

If you lose power with it latched closed it will stay closed. Is that a problem? I don't know. It's just odd. It would work, but its the same weight, size as a #24115 Van sells for $17. Latching relays cost about double. Changing to a latching relay saves 0.60 to 0.75 amps. Is it worth it? To each his own. The latching relay might be a nice device to isolate a back-up buss?

Originally Posted by Steve Sampson

Having got that far though you might start wondering (as I am) if you still want a starter contactor on the firewall since you have one on the starter unit. I am considering ditching the starter contactor and using a simple relay just to switch on the power to pull the solenoid in. The relay is because you have to switch 30 amps which is required initially to pull the solenoid. Once you have wired it this way, you might as well send the alternator power back down the starter cable also! Saves a bit more weight. I am still thinking about it, but would welcome comments....if you have followed this far.

I think its a toss up. If you ditch the firewall starter relay you will need one of those BIG 35 amp starter buttons. I think they are cool but they are big and need a 5/8" dia hole.

Many do run the alternator down the starter. Personally I like a separate B-lead, run to a pull-able CB in the panel. The reason for that is I run a stock internally regulated alternator. Having the panel CB gives me some absolute control of disconnecting the alternator manually with the CB. Plane Power & B&C alternators can be shut down manually with the ALT switch, so access to the B-lead fuse/CB is not needed. Also I'm not totally comfortable with a HOT starter cable all the time. So per my other diagram, I would replace the big ANL fuse with a firewall relay. I still like the idea of getting rid of the big master relay however. I have a cool solid state relay for the job of providing power to the main buss.

Originally Posted by Rick S.

I notice that these relays getting pretty hot during operation. I seen this referenced before as anywhere from warm to hot....I put mine in the"hot" category. Any input regarding the heat generated by the relay while in operation? I have one to control my avionics master power.

Yep that is normal. That is why builders want to get rid of it; it seems like a waste of electricity. On the other hand, its less than 1 amp. It is somewhat a waste but its part of the business of holding down a big high current master contactor.

1 amp x 14.5 volts is 14 watts, and yes it GETS HOT. You can't hold it after a minute. Of course there are other HOT things under the cowl. The more AMP capacity a relay has, the stronger the coil needs to be to hold the contacts down. That's why you hear "CLACK" when you hit the master. Smaller relays can get away with less contact pressure and therefore smaller coils, which are lighter & take less current. Like everything there are trade-offs with "New Better Improved Ideas". The old ideas still work and have their trade-offs.