Amphibious HEMTT

[WaterH]

So yesterday I installed a relay before the starter and it starts every time. I also installed a second 75 amp relay on the AC fans. (One for each fan) and it appears to work fine. The 75 amp is overkill for one fan but I had them As aposed to buying two smaller relays or one higher relay. We’ll see how it works.

In other news, the wiper motor is working fine now. The problem with them not parking maybe because they go to fast when the window is wet. I know they won’t park if I remove the arms. The drag of the arms makes them go slow enough to allow the park system engage. Not really sure how to fix this. I guess I could just let them run till they dry enough and shut off.

I also ordered some new thermostats for my rad fans. But I still think I will wire one to a dash switch. This kind of sucks because I only have extra switches available in my upper console. I would prefer this switch in the lower one. So I may have to move something else up.

 

[Bebop]

I’m not going to say I completely understand that, but assuming it is correct, are you suggesting that wiring it like an aircraft results in more danger to relays? I don’t quite get that.

I would wire your fans to individual relays, trigger them from an ignition switch (and a series temp switch if you want) so that you can turn them off before you disconnect the battery.

I would also not run your electrical system off of the alternator only, but that's just my opinion.

You have a land vehicle, not an aircraft.

I'm not super familiar with the wiper motor issues, so I'll let you figure that one out.

 

[WaterH]

I would wire your fans to individual relays, trigger them from an ignition switch (and a series temp switch if you want) so that you can turn them off before you disconnect the battery.

I would also not run your electrical system off of the alternator only, but that's just my opinion.

You have a land vehicle, not an aircraft.

I'm not super familiar with the wiper motor issues, so I'll let you figure that one out.

So you are saying that it hurts a relay to cut all power before “unlatching” the relay? Not saying your wrong, just I’ve never heard of this. In a standard car, when you shut off the ignition key, you cut all power.

Maybe you don’t understand what I have. It’s basically the same as a standard ignition except that I turn the first click with a separate switch. Then I start the truck with the key.

You do not run the electrical system off the alternator unless you have an emergency. I always shut the truck down before I shut the battery switch off.

 

[Bebop]

So you are saying that it hurts a relay to cut all power before “unlatching” the relay? Not saying your wrong, just I’ve never heard of this.

Yes, very much so given that with your wiring, the power side of a fan is back feeding in your trigger after you cut it off.

In a standard car, when you shut off the ignition key, you cut all power.

No you don't, you just cut the trigger side, not the power side, which is the big difference here with your setup.

Maybe you don’t understand what I have. It’s basically the same as a standard ignition except that I turn the first click with a separate switch. Then I start the truck with the key.

The problem is not during start up but shut down.
How do you shut it down ?

You do not run the electrical system off the alternator unless you have an emergency. I always shut the truck down before I shut the battery switch off.

10-4. I still wouldn't advise it. Ground path seems iffy.

 

[WaterH]

Yes, very much so given that with your wiring, the power side of a fan is back feeding in your trigger after you cut it off.

I could be wrong, but I have a real hard time believing this. There is no contact between the trigger and the line that it connects. When I shut off the power To the trigger, how would the trigger know if there’s power on the line or not? So whether the power is lost on the trigger first or the line first, I can’t see any issue. Do you have any reference that explains this?

Quite honestly, you are one of the people on this site I have a great respect for, but I think you got this wrong. Im happy to be proved otherwise.

On another front, the two 75 amp relays that were sticking on the AC fans are now installed on each fan. They seem to be working. But since they did stick in the past, can I expect them to fail or stick now that they have reduced load? I guess I should replace both of them with new ones.

Edit, some searching got me this. Nothing about back feeding a trigger.

Relay Failures: Why do Relays Fail? With All Aspects!

The relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field that changes the switch contacts. Although

www.electricalterminology.com

 

[IGT]

Look up collapsing field on a relay and read a few hours you might understand what Bebop is talking about.

I have dealt with it in control systems to the point it will burn up a channel on I/O cards.
A lot of newer relays have a blocking diode across the coil wires to prevent this.

I am not saying that is what is causing your problems but a coil in a relay has stored energy that has to go somewhere when de energized.

 

[Bebop]

As IGT said, flyback is a problem

Here is a simplified and easy to understand explanation:

What is a Flyback Diode?

You see them next to DC relays. How do they work?

www.douglaskrantz.com

Then you combine that with the load dump condition (comes from all the fans and alternator) that happens when you shut your battery / kill switch without stopping your engine before switch opening

Load dump - Wikipedia

en.wikipedia.org

it results in terrible high voltage spikes through your relays which will kill them promptly.

Easiest way to prevent this from happening is to wire an ignition switch powering all relay triggers. Opening it before opening the main battery / kill will remove the flyback and load dump path to the relay coils.

 

[WaterH]

As IGT said, flyback is a problem

Here is a simplified and easy to understand explanation:

What is a Flyback Diode?

You see them next to DC relays. How do they work?

www.douglaskrantz.com

Then you combine that with the load dump condition (comes from all the fans and alternator) that happens when you shut your battery / kill switch without stopping your engine before switch opening

Load dump - Wikipedia

en.wikipedia.org

it results in terrible high voltage spikes through your relays which will kill them promptly.

Easiest way to prevent this from happening is to wire an ignition switch powering all relay triggers. Opening it before opening the main battery / kill will remove the flyback and load dump path to the relay coils.

I read and understand both references. Neither of them refer to what you are saying. The first talks about shutting off a relay and it’s effects on the magnetic switching function. There is no mention of weather power is going through the contacts. (that is irrelevant.) When they say inductive device, they are talking about the magnet in the relay, not what the relay is switching. They also mention that most all relays have fly back diodes to prevent damage.

I read the second reference even though I’m very knowledgeable on “load dump”. On aircraft, you don’t ever switch off the battery when it‘s in a high charge rate because the alternator will not ramp down quick. Once the battery is charged back up from the motor start, you can switch off the battery without issue. There is also a alternator switch so you can shut down the field if you so choose.

The relay that was giving me trouble was on the AC fans. I always turn off the AC before shutting down the engine and I always shut down the engine before turning off the battery. So your idea about switching off the trigger before the battery I have already been doing since day one and the relay failed. It failed in a “stick on“ condition. In the reference I linked, it said that was caused by too small of a rating. I think it’s obvious that was the problem.

 

[Bebop]

I must not understand how your stuff is wired then. Can you explain again what is the particularity of « wiring it like an aircraft » so I can see where I’m missing the point.

A diagram would be amazing.

Thank you

 

[WaterH]

Look up collapsing field on a relay and read a few hours you might understand what Bebop is talking about.

I have dealt with it in control systems to the point it will burn up a channel on I/O cards.
A lot of newer relays have a blocking diode across the coil wires to prevent this.

I am not saying that is what is causing your problems but a coil in a relay has stored energy that has to go somewhere when de energized.

I do understand “collapsing field” and I agree that it can fry the contacts on a relay that is not rated for it, but whether the relay is shut off from a switch on the dash or a main power solinoid makes no difference.

 

[WaterH]

I must not understand how your stuff is wired then. Can you explain again what is the particularity of « wiring it like an aircraft » so I can see where I’m missing the point.

A diagram would be amazing.

Thank you

I have no working drawing program anymore. Basically, I have two 500 amp solenoids, one on each battery. I must switch one or both on to have power to the main bus bar. The bus bar supplies power to most of my switches. My switches are resettable breaker switches. (Each one having an amp rating for whatever they are controlling.) There are a few items that I didn’t want to run heavy wire to my cab and back. (Like Fans) In those cases, I’m running a fuse and a relay to the item. Pretty simple really. The only real difference is I can switch off the battery (s) and/or alternator while leaving the motor running.

 

[Bebop]

I do understand “collapsing field” and I agree that it can fry the contacts on a relay that is not rated for it, but whether the relay is shut off from a switch on the dash or a main power solinoid makes no difference.

Yes it does

 

[Bebop]

I have no working drawing program anymore. Basically, I have two 500 amp solenoids, one on each battery. I must switch one or both on to have power to the main bus bar. The bus bar supplies power to most of my switches. My switches are resettable breaker switches. (Each one having an amp rating for whatever they are controlling.) There are a few items that I didn’t want to run heavy wire to my cab and back. (Like Fans) In those cases, I’m running a fuse and a relay to the item. Pretty simple really. The only real difference is I can switch off the battery (s) and/or alternator while leaving the motor running.

Pen and paper not good ?
What you’re describing is a simple battery switch. Nothing aircraft specific.

In case of the fans, do you pick the power for the fan relay and trigger side of the relay from the buss bar ?

 

[WaterH]

Pen and paper not good ?
What you’re describing is a simple battery switch. Nothing aircraft specific.

In case of the fans, do you pick the power for the fan relay and trigger side of the relay from the buss bar ?

Yes, everything gets power from the bus. (Eventually) The trigger power goes through a Breaker switch first.

 

[rattle_snake]

Bebop has good points above. Potential or existing issues can be fixed/mitigated, once we have a complete schematic that has been through review cycle and released into database.

You may also want a copy of that schematic when things quit working on side of road or trail.

 

[WaterH]

Bebop has good points above. Potential or existing issues can be fixed/mitigated, once we have a complete schematic that has been through review cycle and released into database.

You may also want a copy of that schematic when things quit working on side of road or trail.

I agree, but difficult to produce without a drawing program. If I ever want to sell the truck, it’s likly the new owner would want it. I do have a “build list” of where I got parts. Nice to have when something fails. I’m also putting together a “operating instructions” so someone knows how to start and drive it.

 

[Treefrog]

I agree, but difficult to produce without a drawing program. If I ever want to sell the truck, it’s likly the new owner would want it. I do have a “build list” of where I got parts. Nice to have when something fails. I’m also putting together a “operating instructions” so someone knows how to start and drive it.

Draw.io is a pretty decent free drawing program. Not dedicated to schematics, but does ok at them.

 

[Bebop]

Yes, everything gets power from the bus. (Eventually) The trigger power goes through a Breaker switch first.

then you absolutely have flyback and load dump issues

 

[WaterH]

then you absolutely have flyback and load dump issues

I suppose it depends on how you define “issues”. I would say issues means problems. I’ve driven the truck over 3,000 miles now and don’t have any fly back or load dump problems. I’ve flown over ten thousand hours in aircraft with the same wiring and have not had fly back or load dump problems.

You could say IF you turn off the battery right after you start the truck, you may have a load dump problem. But that’s kind of like saying IF you wreck into a tree, you may have bumper problems. As far as fly back problems, it appears (from everything I’ve read) that most relays have protection diodes to prevent that, so I don’t really know how I could have problems like that.

You still have not posted a link where reference is saying “never run the power to your relay through a switch.“ I have searched. We may have to agree to disagree.

 

[Bebop]

No fancy program but I can draw shit stuff on MS Paint, like you should be able to too.

Is that your circuit ?

 

[WaterH]

Yes, pretty much. The trigger switch would be a 5 amp breaker. In the case of AC, there is a trinary pressure switch interrupting the ground.

 

[Wuz-A-zuk]

Is that your circuit ?

Yes, pretty much. The trigger switch would be a 5 amp breaker. In the case of AC, there is a trinary pressure switch interrupting the ground.

then you absolutely have flyback and load dump issues

X2, just because you haven't had issues YET doesn't mean you won't. Not sure how many reputable members need to tell you this.

 

[Bebop]

Fly back when you close the battery switch with the relay still latched.

 

[chaplinfj60]

so i been trying to follow along for a couple day now, this is like above my head in some many different levels but from what i see is if the relay is turned off first no issues correct, but if you just shut main power off first ,it back feeds potentially correct.

i had something similar to this a couple years back with my wiring, if i shut off main power before ignition the alt would back feed. if i recall

 

[Bebop]

so i been trying to follow along for a couple day now, this is like above my head in some many different levels but from what i see is if the relay is turned off first no issues correct, but if you just shut main power off first ,it back feeds potentially correct.

i had something similar to this a couple years back with my wiring, if i shut off main power before ignition the alt would back feed. if i recall

Bit different in this case
But the premises are identical. If you don't shut your devices before switching the battery off, you're setting yourself for failure.

 

[WaterH]

Again, you need to define “issue”.

Fly back when you close the battery switch with the relay still latched.

I agree that this may be happening if I left the trigger switch on, but the relay is protected, so in my mind, no issue. Would the relay be “more protected” if we switched the trigger off first? (As I usually do) Maybe. But I’ve had zero problems so far with this.

And before you say it, my only relay failure is sticking contacts which is obviously from using an under rated relay.

I did some thinking on this and the only relay circuit that would be “on“ is the radiator fan. It is fired by a thermostat. One or both fan circuits will almost certainly be on when I shut the battery off. This is every time in those 3000 miles. The relays associated with them work perfect. I am having trouble with one of the thermostats. Might be related to this or might be Chinese junk.

 

[chaplinfj60]

Bit different in this case
But the premises are identical. If you don't shut your devices before switching the battery off, you're setting yourself for failure.

thats what i was gathering from the pic

 

[Bebop]

Again, you need to define “issue”.


I agree that this may be happening if I left the trigger switch on, but the relay is protected, so in my mind, no issue. Would the relay be “more protected” if we switched the trigger off first? (As I usually do) Maybe. But I’ve had zero problems so far with this.

And before you say it, my only relay failure is sticking contacts which is obviously from using an under rated relay.

I did some thinking on this and the only relay circuit that would be “on“ is the radiator fan. It is fired by a thermostat. One or both fan circuits will almost certainly be on when I shut the battery off. This is every time in those 3000 miles. The relays associated with them work perfect. I am having trouble with one of the thermostats. Might be related to this or might be Chinese junk.

The relay is not protected against that, as I just showed you.

But you do you.

I'm just pointing out (one of) the issues with the way things are wired in your car.
If you added an ignition switch to control the power to all relay triggers, you wouldn't have this problem.

Again, there is a reason why nobody does it like that.

 

[Bebop]

thats what i was gathering from the pic

What may be fine for a "emergency kill switch" operation shouldn't be used as a normal state of doing things.
Nowadays, kill switches have delays in order to let the load dissipate properly before shutting the power off.
Electronics are really sensitive to this and there has been many fried ECUs from improperly wired switches.

 

[WaterH]

so i been trying to follow along for a couple day now, this is like above my head in some many different levels but from what i see is if the relay is turned off first no issues correct, but if you just shut main power off first ,it back feeds potentially correct.

i had something similar to this a couple years back with my wiring, if i shut off main power before ignition the alt would back feed. if i recall

That is the load dump scenario. You can do that and not hurt anything. It is only a problem if the alternator is in a high charge rate and you remove a large load. For example, you are flying With landing lights on and only power is the alternator. The alternator will power the landing lights just fine. But if you switch them off, there is a brief period where the alternator is sending “landing light” power to the bus and there is no place for it to go. (Because you have the battery off line.) In that case, you might fry your radio. (If it’s still on)

The most likly scenario is you just started the engine after cranking for a long time. The battery is low because you took so long to start it. The alternator is in “high charge” to replenish the battery. You accidentally turn off the battery. That high charge goes in to everything you have turned on.

Bit different in this case
But the premises are identical. If you don't shut your devices before switching the battery off, you're setting yourself for failure.

There are pluses and minuses to wiring like this. But I don’t think aircraft manufacturers are setting people up for failure.