JD Seller Trailer Isolation Relay

JD Seller,
Over the weekend you posted about a way to isolate your vehicle charging system from your trailer while using the trailer pump. I think it was pretty much answered, but I thought a sketch might help.I think you could do it with a 12v two pole relay, with one normally open contact and one normally closed.
Pete

I would not bother with that N/O between the trailer battery and the winch. There would be a high amperage draw across it and really no reason I can think of to break it. You would just want the N/C contact between the trailer and vehicle to open when the winch was running to eliminate draw on that line. That way the relay would only have to be heavy enough to handle the charging current.
I would have to see how the winch was wired to recommend where to pull power off of it to energize the isolation relay but when it was energized would be the only time you would need break the connection.

Good point. As long as the charging circuit opens up when the pump motor is energized it should work

FWIW I agree with you Chris. The winch could draw as much as say around 30 to 100 amps+ or more depending on its size and the load and since its to always be fed from the trailer battery anyway, (NOT the truck battery) there's no need to have a high current rated relay in that circuit. Conversely, the relay in the charging circuit only needs to be say around a 30 amp subject to the fuse and wiring from the truck battery back to the trailer battery.

As you noted, its only necessary to configure the circuit so when driving down the road the truck can charge the trailer battery and 20 to 30 amps can suffice for that. Then in order to prevent a high current draw by having the truck and trailer batteries remain in parallel when the winch is to be operated, the Normally Closed relay in the charging circuit can be opened (a simple 12 VDC feed via the winches activation relay circuit) upon activation of the winch.

As my sparky friend Jim noted JD intends to use different trucks to pull that same trailer so having the necessary relay back as part of the trailer wiring system makes most sense. Either a toggle switch or a relay can accomplish that but I prefer a relay so the breaking of the charging circuit is automatic versus possibly forgetting to flip the toggle switch each time.

If the charging circuit has a simple Normally Closed 30 amp 12 VDC coil operated relay back at the trailer, its simple to send it 12 volts to open the circuit anytime the Winch is activated and that should be easy as the winch itself probably has one of its own relay terminal that's hot when a button (raise or lower, in or out) is depressed.

Oh well, there are many many ways to do it and to each their own.

John T

I've been thinking this over for a couple days, no really easy solutions come to mind.

As I recall, he has 2 motors on the trailer, a winch motor, and a lift gate.

The winch will have 2 power relays that control the motor, one for each direction.

The lift gate will have one power relay that controls the up direction. The down will only be a solenoid valve, so not a concern.

As I see it, the easiest way would be to have 3 NC control relays, wired in series in the charge circuit. The coil of each control relay would be powered by the same signal that controls each power relay.

When ever any motor was in motion, one of the control relays would be energized, opening the contacts, opening the charge circuit from the vehicle.

Yo Steve, as far as that goes, how about JUST ONE NC RELAY in the charging circuit instead of three??? and with the 12 Volt signal feed from each source (Up Winch,,Down Winch,, Lift Gate) having a diode in series so any of the three signals can open the charging circuit relay but none can back feed or interfere with the other ?????????

I haven't drawn it out or thought it through completely so no warranty, just an off the cuff quick thought so he only needs ONE NC relay instead of three. There may be a back feed or other problem why only one relay with diodes may not work, but Im in a hurry, need to get back down to the shop, I will look back later..

John T

Put a quality self-resetting circuit breaker in the "charge" line that is rated lower than the fuses that sometimes blow.

End of problem, and NO complicated circuits or added wiring needed.

Yes, diodes would work. Just thinking the relays would be more bullet proof.

Pete:

Why even bother with a Relay at that point, when all you need is a Blocking Diode between the Charging Line & the Battery. A Diode is nothing more than a ONE-WAY GATE, Current can go through it in one direction ONLY. If you are removing Current from the Battery, ie Winch, Hyd. Pump, etc., then you need to be replacing that Current - which WON"T happen if you have an open relay on the Charging Line.

:>)

Bob, Ive slept since his initial post, I forget now what the original problem was lol. In my trucks or RV when I have wired a charge line circuit to charge the towed vehicles battery when I'm driving, I simply use a 20 or 30 amp self resetting circuit breaker, never a problem. If he had (forget what he had now) BOTH fuses and circuit breakers and since all he needs is a low current charging circuit, a 20 amp self resetting breaker and a 30 amp fuse (like what you're talking about) ought to do the trick. Seems like he mentioned a relay?? or maybe it was some of us who jumped on the relay bandwagon...I cant remember what I had for lunch let alone all the topics I post to lol

John T

Bob for some reason he did not like that solution. We have been doing that on three trailers for years with NO problems. Have one set up just as his winch and folding tail with Three trailer mounted batteries and most times they stay charged .

I don't know how the other makes are set up but the Ford trailer tow charging wire is run through a fuse that feeds a relay that supplies the charge circuit at the plug. This circuit is only live with vehicle key on so if you shut the truck off while running the winch you shouldn't be able to damage anything on truck as the relay opens the circuit when the key is off. I would assume all makes similar , shut truck off seems easier , you aren't going to recharge the batteries in the few minutes you are running winch, they will charge on the way there and back while driving. Maybe if you are using winch a lot with limited driving having some kind of a battery charger on the trailer while parked would be a better long term fix. Your system would no doubt work but reminds me of the automakers efforts to make things more complicated than they sometimes need to be . But I just like to keep stuff as simple as possible.

I have a 99 F550 that I pull a hydraulic tiltbed trailer with a winch,I leave the engine running most of the time to keep charging the battery when using the tiltbed and the winch but have never had a problem like was described.But I always keep a good strong battery on the trailer.

d i had a winch on my trailer for about 15 years now,, pull it with a 99f350and a 2012 f250 never blown a fuses but i also have a a disconnect well to it just a blade spade connector that i can disconnect i know it not all fancy but does the job.

Thanks for the ideas fellows. Here is how the current batteries are installed and how the dove tail/winch work.

1) I have the single factory battery at the hydraulic supply for the dove tail. The dove tail is powered up and down. This battery has a several ways to charge it. A)There is a maintainer/charger mounted right there. It can be ran off of 12v or 110volt power supply. B)It also has a solar panel on the top of the gooseneck that helps to keep it charged. C)Then you have the charge wire from the pickup.

2) The winch is mounted on a cross member between the gooseneck hitch up rights. I have two deep cycle marine batteries, 1100 CCA Each, in a box right above the winch. The cables only are about four foot long. These batteries are only charged by the truck charge wire. The winch really sings with these two batteries running it. It is a Warn 12,000 LBS winch.

The winch batteries and the dove tail lift battery are not wired together for shared power transfer. The truck charge wire is the only common link between the two.

I was thinking hard about how to wire an isolation relay. I would need to use diodes to keep the functions from cross feeding each other. It seems to get quite complicated wiring wise real quick. LOL

Bob and jm. I did not see your reply about just installing a smaller circuit breaker on the trailer side of the charge wire. This sounds like the simplest way. I would just have to check all of the trucks and see what AMP breaker would be smaller. I think 25 amp would work as it seems that the trucks all have 30 amp fuses.

One of the reasons I want to get something done is that unplugging the trailer light wire has cost me two plugs. If you are rushed when loading it is real easy to forget to plug the light wire back in. So you take off dragging it on the ground. Plus you don't have brakes when you may need them too.

I don't want it to get real complicated wiring it. That just makes too many things that can fail and then you are back to square one.

I also do not want to do major rewiring on the trailer. One of the big reasons for this is I more than likely will trade this trailer every few years. I usually keep them in pretty good shape. So about the time the tires and brakes need replaced I usually just trade for a new one. Doing that has made it cost me less than a $1000 a year to own the pervious trailers. I also usually need the depreciation for tax purposes.

THANK YOU all for the ideas.

Dr. Walt,
A diode would have to be wired to allow current to flow toward the trailer to charge the batteries. It would seem that it would then also allow the overcurrent to flow to the batteries when the motors are used
Not to seem too simplistic, but would a simple resistor in the charging circuit allow charging current to flow, but limit the current during high amp draw? (similar to a ballast resistor)
Certainly gives us something to noodle on doesn't it
Pete