Yes! Excellent! We can continue to add complexity to the model!
Now we’re having a technical discussion based on the fundamentals so we can discuss the trade offs!
Trailer power
- Thread starter clrussell
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
Now we’re having a technical discussion based on the fundamentals so we can discuss the trade offs!
This got a bit buried, but I'm inclined to think you're correct that there's 40A available at the trailer plug. I checked my fuse box and saw that the "SUB BATT" fuse was noted as 40A but it seemed to be located inside a large blade of fuses? I haven't seen one of those before. I gave a couple pulls, but didn't try too hard to dislodge it. Anyone else want to give a try to confirm that this is the correct fuse?
FrazzledHunter
SILVER Star
I'm assuming on mine that what's listed is what's actually under there as it's never been touched but I've never pulled that thing either. Is it supposed to pull all the fuses at once or is it just a cover? If it pulls all the fuses I'd think you'd risk breaking it.
On a semi-related note the literature from the manufacturers of trailers is, in my experience, universally mum on this subject. On my "must ask" list of questions for trailer dealers is whether or not the trailer uses that line, for what and how much current does it draw. I have asked dealers those questions and they either didn't know or the one that said it did couldn't tell me for what and/or the current rating.
I was recently looking at an InTech OVR and asked the dealer the above questions and they assured me that line was used to charge the battery but couldn't tell be what the draw was. So I said that to sell me the trailer he'd have to put that and the current draw on the bill of sale. They said they'd get back to me. Three guesses as to whether or not they ever did.
On a semi-related note the literature from the manufacturers of trailers is, in my experience, universally mum on this subject. On my "must ask" list of questions for trailer dealers is whether or not the trailer uses that line, for what and how much current does it draw. I have asked dealers those questions and they either didn't know or the one that said it did couldn't tell me for what and/or the current rating.
I was recently looking at an InTech OVR and asked the dealer the above questions and they assured me that line was used to charge the battery but couldn't tell be what the draw was. So I said that to sell me the trailer he'd have to put that and the current draw on the bill of sale. They said they'd get back to me. Three guesses as to whether or not they ever did.
Last edited:
At least they're not lying with a blanket answer. Having been on the RV forums for awhile, the reality is there's too many variables to control for. It's not just the trailer either, but the interaction with the towing vehicle. Where some tow vehicles have a old school, temp compensating, or smart alternator. The wire and condition to the 7-pin receptables. How much draw, which can create voltage drops of .1V to over 3.5V. Then on the trailer side, wires, types of batteries, state of charge, solar, etc.
The anecdotal answer is it can be up to ~15 amps input to the trailer batts or even negative amps back to the tow vehicle. The reality is it's closer to 5-10 amps for traditional lead acid batts.
A DC-DC charger is always a good answer regardless of the other variables as it steps up voltage, provides a charge profile tailored to the battery type, and proper isolation. A common aha moment for many that upgrade to a DC-DC to support lithium, is to realize the advantages that could have been had even with lead acids.
This. If I'd done this right the first re-wire, my marine 110AH AGMs in the trailer would have lasted much longer. They never saw a full charge even after 8+ hours driving or solar charging while base camping. They only got proper charging when on shore power.
As to the "maths", that's all good information, but it goes to sh*t with one sketchy crimp connection. Buy tinned marine wire and lugs. A proper crimp doesn't require a crimp-then-solder. It makes for a brittle junction that can't handle mechanical stress. Use sealing heat shrink tubing on all junctions.
These are awesome for down to 8AWG crimps.
That 40amp is the correct fuse. .. ask me how I know this LOL.
Seems the safest way to do this is just use the Dc - DC with a lithium if you need a quick charge. This is what I have setup now. I also switched to 40 amps as this will re-charge the battery in 2 hours. 20 amp DC to DC you need 4 hours of driving time to recharge the battery if I remember right?
If traveling everyday the ACID or AGM with the trailer power line is fine. Cheep and not complicated. I did this for years without issues.
I don't under stand the issue running the AGM with the trailer cord power line? Many trailers come with that setup from the factory.
Seems the safest way to do this is just use the Dc - DC with a lithium if you need a quick charge. This is what I have setup now. I also switched to 40 amps as this will re-charge the battery in 2 hours. 20 amp DC to DC you need 4 hours of driving time to recharge the battery if I remember right?
If traveling everyday the ACID or AGM with the trailer power line is fine. Cheep and not complicated. I did this for years without issues.
I don't under stand the issue running the AGM with the trailer cord power line? Many trailers come with that setup from the factory.
In my mind there are two concerns:
1) The alternator on the 200 doesn’t put out high enough voltage to fully charge an AGM on its own. This yields less capacity than the battery is rated for and a shorter lifespan.
2) The in-rush current when charging starts is (to a first order) enough to blow the 40A fuse in the cruiser. We showed in calculations that the parasitic resistances should be enough to limit the in-rush current, and there seems to be anecdotal evidence of people doing this with success.
Both of these would lead me away from implementing a direct wire-to-battery solution and lead me away from recommending it to others. But could be meet the constraints and risk tolerance of someone else. My day job is designing electronics to be produced in the millions and they all need to work, so that colors my perspective for sure.
FrazzledHunter
SILVER Star
Slightly off topic but I wanted to find out how one particular vendor used that power line on the 7 pin, if they actually did at all.
So I wrote to inTech and asked about their 7 pin utilization. They replied!!! Kudos to them!!!
NOTE: the "off grid package mentioned below is an option that consists of: "400 watts of solar, mixed with an MPPT charger controller, 200 amp hrs of lithium batteries, and a 2,000 Watt inverter".
Here's what they said - I'm paraphrasing a bit:
Yes, the trailer will receive a charge from the tow vehicle while in traveling. Typically, this is limited to just a few amps, but some of the newer trucks do have a more robust charging system. You will have to check with your tow vehicle manufacturer about the exact specifications. This will not change the if you have the “off-grid package.”
Nuts. I was hoping for something like 20A. So I wrote a second time asking whether or not the charging would continue to occur on the 7 pin if I opted for their "off grid" package - their 2nd reply:
Yes, as long as you have some light on the panels there will be some charge going to the batteries. This will supplement the charge coming from the tow vehicle or shore power. The charge controller will manage that power as needed. If the batteries are full it will no longer allow the charge into the batteries.
So with exactly 1 authoritative data point, I take from this that RV trailer vendors who might actually use that line really can't do so with any significant power draw. The LC is overbuilt.
We have used a 100Ah battery for weeks at a time, charging it by 170W solar panels, the Land Cruiser via a Victron Orion at 360W and a 1000W gas generator powering a 600W charger. We also know how long it takes to charge at the different wattages. What I conclude is that I would like to charge a trailer's batteries with at least 360W coming from the tow vehicle. This triggers 3 upgrades to the tow vehicle and 1 to the trailer if I want to charge the trailer and everything else while towing:
So I wrote to inTech and asked about their 7 pin utilization. They replied!!! Kudos to them!!!
NOTE: the "off grid package mentioned below is an option that consists of: "400 watts of solar, mixed with an MPPT charger controller, 200 amp hrs of lithium batteries, and a 2,000 Watt inverter".
Here's what they said - I'm paraphrasing a bit:
Yes, the trailer will receive a charge from the tow vehicle while in traveling. Typically, this is limited to just a few amps, but some of the newer trucks do have a more robust charging system. You will have to check with your tow vehicle manufacturer about the exact specifications. This will not change the if you have the “off-grid package.”
Nuts. I was hoping for something like 20A. So I wrote a second time asking whether or not the charging would continue to occur on the 7 pin if I opted for their "off grid" package - their 2nd reply:
Yes, as long as you have some light on the panels there will be some charge going to the batteries. This will supplement the charge coming from the tow vehicle or shore power. The charge controller will manage that power as needed. If the batteries are full it will no longer allow the charge into the batteries.
So with exactly 1 authoritative data point, I take from this that RV trailer vendors who might actually use that line really can't do so with any significant power draw. The LC is overbuilt.
We have used a 100Ah battery for weeks at a time, charging it by 170W solar panels, the Land Cruiser via a Victron Orion at 360W and a 1000W gas generator powering a 600W charger. We also know how long it takes to charge at the different wattages. What I conclude is that I would like to charge a trailer's batteries with at least 360W coming from the tow vehicle. This triggers 3 upgrades to the tow vehicle and 1 to the trailer if I want to charge the trailer and everything else while towing:
- Upgraded alternator - I already have a REDARC charging a 2nd battery - 25A max and I charge the existing 100A battery - 40A max.
- Wiring from the engine bay to the rear of the Land Cruiser
- A DC-DC charger (where will it live: In the trailer or in the LC?)
- Connector and wiring to the trailer battery
I've been noodling on a couple of the same things including upgraded alternator and auxillary Anderson. I just experienced an alternator failure at 160k miles and replaced it with OEM as it was during a road trip. Perhaps of my own doing pulling ~50A in supplementary draw including 18A for onboard house battery, 20A DC-DC in trailer, and 12A in various electronics including cell booster. Unknown is how much extra my FLA group 31 starter batt pulls in low states of charge. Wish I could have planned an upgrade to the alternator. Though others with pretty stock setups have experienced alternator replacement at this mileage too? Either way, I'm going to be more conservative in how much extra load I'm putting on it.
What type of trailer are you supporting?
If I'm being honest, for my 27' Airstream with 400W of solar and 400Ah LifePO4, I already have a perpetual power machine from solar alone. The addition of more DC-DC is as a backup or if I wanted to run the A/C. I'm looking to add a 10 cu ft 12V compressor fridge and that may need more load support. Or not. Point is, do you already have significant solar on your trailer?
FrazzledHunter
SILVER Star
We're shopping for a trailer, one that would maybe be a little more rugged. The inTech I mentioned had optional 200Ah batteries and claimed 400W solar. Ummm, I'd like to see that on a watt meter.
We had a Keystone Hornet 33F from 2001-2016 and ran it to death. What I absolutely hated was not being able to run the fridge while under tow. We looked into adding batteries and an inverter just to run the fridge but it was too expensive. Having some experience with trailers and having "seen it all" in campgrounds we're being careful, in fact hesitant, about getting back into it. We do like AirStreams a lot but couldn't afford a new one at the time we bought the Hornet. (Too afraid at the time to buy a less expensive used one. We would now.) Perhaps we should look at them again.
BTW, I followed your write-up about replacing your alternator while on the road. I was feelin' it with ya. What a drag.
FrazzledHunter
SILVER Star
I've used Powerwerx and they're a great outfit.
I was also looking here for my dream project of getting power to the rear of the LC:
Trailer Vision – Trailer vision - https://trailervision.com.au/
They're also represented on Amazon:
Trailer Vision - https://www.amazon.com/stores/TrailerVision/page/4640ED56-0894-4611-A430-1D4B011BA072?ref_=ast_bln
I've got two sets of their mountable SB50 (source/load) connectors if you're interested. Going to be a while before I'd be able to ship though.
Those are the ones. Don't know why i didn't check Powerwerx. Gave up on Amazon and just finally had a shop order them with a bulk buy from a distributor.
FrazzledHunter
SILVER Star
Thanks! I don't even have a trailer yet LOL. I'm still trying to think through how I'd even do this. I'm not sure I can without some custom mod to the trailer which, as a practical matter, might not even be possible for me.
Wit’s End sells Anderson Plug goods too. He makes lots of stuff for 80s, but I don’t see his stuff mentioned as much here in 200 land. Definitely worth a browse around his site and support an LC-specific vendor!
absolute-wits-end.com
Anderson SB50 Environmental Boot- Load Side
Anderson SB50 Environmental Boot- Load Side (AEB-50L)
FrazzledHunter
SILVER Star
Anderson also supplies a list of vendors for their products and accessories via their website. REF:Wit’s End sells Anderson Plug goods too. He makes lots of stuff for 80s, but I don’t see his stuff mentioned as much here in 200 land. Definitely worth a browse around his site and support an LC-specific vendor!
Anderson SB50 Environmental Boot- Load Side
Anderson SB50 Environmental Boot- Load Side (AEB-50L)
SB®50 Boot, With Cover, Load - https://www.andersonpower.com/us/en/shop/sbr50-boot-with-cover-load.html
Definitely worth a shot, but not sure what's up with Joey. Tried to ping him a while ago about ARB fridge plug to SB50 pigtails he'd been fabbing and didn't hear back.Wit’s End sells Anderson Plug goods too. He makes lots of stuff for 80s, but I don’t see his stuff mentioned as much here in 200 land. Definitely worth a browse around his site and support an LC-specific vendor!
Anderson SB50 Environmental Boot- Load Side
Anderson SB50 Environmental Boot- Load Side (AEB-50L)
He seems to be MIA on here since Feb. or so. I've bought lots of 60/100 cruiser stuff from him over the years. Hope he's doing OK.
Dang. He sent an email out around then about changing shop locations as his rent was going nuts. Hope he’s ok, too and just busy with positive things.
Last edited:
FrazzledHunter
SILVER Star
So you want to charge a trailer under tow? 
Perhaps power the entire campground?
I've been looking at alternator upgrades and stumbled across this:
The SBC-DT5.7-660 is a complete dual alternator
charging system specifically engineered for the
Toyota 3UR-FE (5.7L Gasoline) engine. It adds a
12 Volt 660 Amp TWIN secondary alternator
while leaving the OEM charging system
completely intact.
The OEM alternator can also be upgraded to one
of our 12V high output options.
12V 660 Amps | SBC - https://smartbatterycharger.net/product/12v-660-amps/
EDIT: there's also a 780 Amp option. How could I have been so careless to miss this? I wonder if these are intended for the Tundra because for the life of me I don't see how these would fit.
12V 780 Amps | SBC - https://smartbatterycharger.net/product/12v-780-amps/
Perhaps power the entire campground?
I've been looking at alternator upgrades and stumbled across this:
The SBC-DT5.7-660 is a complete dual alternator
charging system specifically engineered for the
Toyota 3UR-FE (5.7L Gasoline) engine. It adds a
12 Volt 660 Amp TWIN secondary alternator
while leaving the OEM charging system
completely intact.
The OEM alternator can also be upgraded to one
of our 12V high output options.
12V 660 Amps | SBC - https://smartbatterycharger.net/product/12v-660-amps/
EDIT: there's also a 780 Amp option. How could I have been so careless to miss this? I wonder if these are intended for the Tundra because for the life of me I don't see how these would fit.
12V 780 Amps | SBC - https://smartbatterycharger.net/product/12v-780-amps/
Last edited:
