Two Power Routes from Tow Vehicle

[AndyRonLI]

Folks,
I have the budget, so I am going the Victron route for my 5th wheel trailer.
Using the Multiplus-II and with the Lynx Shunt and Lynx Distributor.

I currently am using a Renogy DC/DC to isolate my trucks 9 pin battery power and the LiFePo4 batteries I am using (Li-Time/ ampere time).
It is set up to limit draw to 20 amps.

When I trace out the EXISTING 12V trailer wiring there are essentially two groups of loads seperated by a 30 amp automotive type bussmann fuse.
The battery feeds connects to a set of loads on one side of the busmman and the tow vehicle input feeds from the other side of the bussmann
The bussmann lugs are actually being used as multi connect terminal blocks.
I am going to tidy that up by using some actual terminal blocks.

My question is this.
Long range, I would like to upgrade my tow vehicle wiring to allow more current draw from the vehicle.
This would be a separate Anderson connector and 4 gauge wiring to the DC/DC connector.

So my questions are:

Should I feed that tow vehicle load in directly to the 12V circuits or into the Lynx distributor.
Currently the trailer loads are directly feed from the battery, should I pull the loads from the lynx distributor?

The only load that must pull directly from the battery are the brakes. Saftey requirement
Thanks
Andy

 

[justinm001]

I would get a small 12V SLA battery and use the 12V on the 7pin for charge for the trailer brakes and keep that part isolated since you're going with 4gauge.

Everything should feed and draw off the lynx distributor so the 4gauge should go there. Same with trailer loads. Then the battery should be on the shunt side. I'd suggest getting a smartshunt over the lynx shunt. I have both

Lynx shunt: looks nice and has a fuse for positive, also allows the distirbutor lights to turn red/green but doesn't communicate anything so basically pointless. has VEcan (network cable) which is a lot nicer than vedirect. Doesn't have bluetooth though. 1000a

smartshunt: not as clean of a setup but cheaper. uses vedirect which is dumb but has bluetooth and available in 500/1000/2000a. Bluetooth allows it to use vesmart so it can communicate voltage for their MPPT solar chargers that also have bluetooth not sure what else it can do.

 

[AndyRonLI]

This is my current plan for a small distributor box using some Blue Sea Buss bars

 

[AndyRonLI]

I do keep thinking of a separate battery, but that becomes one more maintenance head ache. If you look at the more schematic representation I posted, the system is set up so that if your batteries are depleted you can still perform your get out of dodge functions off the tow vehicle. But those functions (or at least some) need to be able to work with the tow vehicle disconnected. Biggest issue I see is that I would need a weird lug for that battery cable, its only 6? 8? and the Lynx has those honking big posts.

 

[justinm001]

I do keep thinking of a separate battery, but that becomes one more maintenance head ache. If you look at the more schematic representation I posted, the system is set up so that if your batteries are depleted you can still perform your get out of dodge functions off the tow vehicle. But those functions (or at least some) need to be able to work with the tow vehicle disconnected. Biggest issue I see is that I would need a weird lug for that battery cable, its only 6? 8? and the Lynx has those honking big posts.

Most trailers that have electric brakes and no 12V loads just have a small SLA battery powered by the 12v pin and no maintenance for years. The battery shouldn't have any loads ever and charged the entire time its used so as long as you're using the trailer every 6 months or so it'll be fine.

I think you're missing the point of the Lynx. Its just a huge buss bar with fuses so everything will work as long as something has or is providing 12V power and the fuses aren't blown. So if batteries are disconnected but tow is connected it'll all work, same if batteries are connected but no tow.

Correct the lugs are different. I've seen people use copper bars and drill holes so one is larger than the other and it'll work. Not nearly as pretty as Lynx shunt though since its seamless but its half the price and has bluetooth which comes in handy troubleshooting without a cerboGX. Although shunts aren't really necessary if you have batteries with BMS that communicate with CerboGX.

 

[AndyRonLI]

So I noticed on Wills video for this system he doesn't have a battery isolation switch. That is generally a given on mobile systems.

 

[justinm001]

So I noticed on Wills video for this system he doesn't have a battery isolation switch. That is generally a given on mobile systems.

Battery isolation switches are kinda pointless in most cases. I have one on my boat where the alternator will charge both batteries but I just turn one on so incase we leave the radio on we can swap to batt#2 and start back up. Not sure of a use case for a battery isolation switch in an RV other than just a salesman switch to turn on/off. But my batteries have breakers built in and I have a fuse on the Lynx shunt and each load has a fuse on the Lynx distribution so can just remove the fuse to turn off.

If doing electrical work I'd rather physically remove a fuse so I'm 100% certain no load over turning a knob. I really like the Lynx distribution as I can easily troubleshoot and reconfigure my system on the road. If my alternator's acting weird I can spend 2 minutes pulling the fuse in the lynx on the side of the road to figure out later.

 

[HarryN]

Suppose that you wanted to move ~ 1 kW from the truck to the trailer. That is roughly 100 amps @12 volts or 10 amps @ 120 vac.

Moving 100 amps from the front of a truck to the back of a trailer using 12 volts - even with a DC - DC charger isn't so easy.

Moving 10 amps @ 120 vac that far is a piece of cake and honestly it is a lot less likely to arc when connecting and disconnecting.

My suggestion is to put a 120 vac battery charger in the trailer. When near a shore power source - plug it in there. When connected to the truck - plug it in to an inverter on the truck.

 

[justinm001]

Suppose that you wanted to move ~ 1 kW from the truck to the trailer. That is roughly 100 amps @12 volts or 10 amps @ 120 vac.

Moving 100 amps from the front of a truck to the back of a trailer using 12 volts - even with a DC - DC charger isn't so easy.

Moving 10 amps @ 120 vac that far is a piece of cake and honestly it is a lot less likely to arc when connecting and disconnecting.

My suggestion is to put a 120 vac battery charger in the trailer. When near a shore power source - plug it in there. When connected to the truck - plug it in to an inverter on the truck.

Converting from 12 to 120 back to 12 is a loss of like 20% The problem isn't the wiring but the alternator and pulling a ton of amps constantly while driving. not sure of his alts but maybe 50-60 amps over the 4 gauge wire, maybe to a pair of 30amp orion DC chargers. Its not really an issue to run that long of wire with anderson connection in the middle.

I have a 50DN alternator in my 40ft coach and the engine is in the back with the 12v components under the front bumper OEM. I'm pulling close to 3000w of 12V from it constantly but that alternator is oil cooled and rated for constant use.

 

[AndyRonLI]

Converting from 12 to 120 back to 12 is a loss of like 20% The problem isn't the wiring but the alternator and pulling a ton of amps constantly while driving. not sure of his alts but maybe 50-60 amps over the 4 gauge wire, maybe to a pair of 30amp orion DC chargers. Its not really an issue to run that long of wire with anderson connection in the middle.

I have a 50DN alternator in my 40ft coach and the engine is in the back with the 12v components under the front bumper OEM. I'm pulling close to 3000w of 12V from it constantly but that alternator is oil cooled and rated for constant use.

Suppose that you wanted to move ~ 1 kW from the truck to the trailer. That is roughly 100 amps @12 volts or 10 amps @ 120 vac.

Moving 100 amps from the front of a truck to the back of a trailer using 12 volts - even with a DC - DC charger isn't so easy.

Moving 10 amps @ 120 vac that far is a piece of cake and honestly it is a lot less likely to arc when connecting and disconnecting.

My suggestion is to put a 120 vac battery charger in the trailer. When near a shore power source - plug it in there. When connected to the truck - plug it in to an inverter on the truck.

So I would never expect to pull 100 amps off my alternator for charging, I would be more than happy with 40 and will willingly settle for 20. A five hour drive pumps 100Ah back into the battery bank, more than enough to cover any usage by the trailer while being towed. The only real load is a 120V AC residential fridge.

 

[justinm001]

What's the fuse rating on your trucks 7 pin? It can be up to 30amps. If so then you can just use that and call it a day

 

[HarryN]

So I would never expect to pull 100 amps off my alternator for charging, I would be more than happy with 40 and will willingly settle for 20. A five hour drive pumps 100Ah back into the battery bank, more than enough to cover any usage by the trailer while being towed. The only real load is a 120V AC residential fridge.

So just to put it into perspective, the energy sticker in my home fridge estimates ~ 2 kW-hrs per day, averaged over a month.

( 2 000 W-hrs ) / 24 hrs ~ 100 watts average draw.

( 100 watts ) / ( 12 volts ) ~ 10 amp just to run the fridge during the drive

It might potentially take 2 fully charged batteries to keep up with it - every day.


Are you sure you don't want some solar on that trailer?

 

[AndyRonLI]

So just to put it into perspective, the energy sticker in my home fridge estimates ~ 2 kW-hrs per day, averaged over a month.

( 2 000 W-hrs ) / 24 hrs ~ 100 watts average draw.

( 100 watts ) / ( 12 volts ) ~ 10 amp just to run the fridge during the drive

It might potentially take 2 fully charged batteries to keep up with it - every day.


Are you sure you don't want some solar on that trailer?

Definitely want some solar, but need the AC/DC infrastructure upgrade first. I find that my current 10amp charging system off the 7 pin works pretty good. The voltage drop to the input side of the DC/DC charger is about 2.5 volts, not great, but not excessive. The 10 amps seems to keep up with the fridge. I currently have two 200ah LiFePo4 batteries (that will be 4 later this month), and I arrive at about the same state of charge as when I left, at least according to my shunt. Hot days it will be down a bit as the trailer itself gets pretty warm, but it wont drain the battery.
I have access to at least a 20 amp plug or better about half the time, and I carry a Honda 3000is generator for those times without power.

Would like to get to a 40 amp tow vehicle charge, that would really keep batteries topped up for a road trip. Not having to run the generator for an overnight stop is a goal. It is the Walmart, Cracker Barrell overnights that can be an issue, some do not allow generator usage.

Solar is next years project!
Thanks
Andy

 

[justinm001]

Definitely want some solar, but need the AC/DC infrastructure upgrade first. I find that my current 10amp charging system off the 7 pin works pretty good. The voltage drop to the input side of the DC/DC charger is about 2.5 volts, not great, but not excessive. The 10 amps seems to keep up with the fridge. I currently have two 200ah LiFePo4 batteries (that will be 4 later this month), and I arrive at about the same state of charge as when I left, at least according to my shunt. Hot days it will be down a bit as the trailer itself gets pretty warm, but it wont drain the battery.
I have access to at least a 20 amp plug or better about half the time, and I carry a Honda 3000is generator for those times without power.

Would like to get to a 40 amp tow vehicle charge, that would really keep batteries topped up for a road trip. Not having to run the generator for an overnight stop is a goal. It is the Walmart, Cracker Barrell overnights that can be an issue, some do not allow generator usage.

Solar is next years project!
Thanks
Andy

The 12V on the 7pin is rated for 30amps. See what your trucks fuse is and if its not 30amps then buy a new plug and run a wire from the battery to that pin. See what the wiring is on the camper side and upgrade if necessary, then run a 30 amp dc to dc charger. This makes a lot more sense than using anderson plugs and all that.You'd be getting close to 10% charge per hour.

Although the effort to increase from 10 to 30 doesn't seem really worth it when you could spend couple hundred bucks and get one or 2 100w solar panels on the roof and get 5000-1000w a day

 

[HarryN]

So if I understand the original question, you are asking where to hook up the connections and how.

So the general idea of connecting to batteries and things connected to (many types of ) batteries is to think of them as 5 000 amp capable sources. This is not always true but close enough for what you are doing.

This is in general true for good quality AGM batteries but some in the battery industry have proposed that LiFe batteries are limited to only a few 100 amps by the presence of the BMS. I am not qualified to say one way or another but both sides have merits.

So when you attach a wire to a battery or bus bar, regardless of if you are planning for power to go "in" or "out", the question that should go through your mind is "if this wire accidentally short circuits - what will happen? "

From this you can decide on how to fuse or breaker protect the wire. It is not physically possible to protect every wire from this issue so sometimes this means just being careful.

As far connecting to the truck starter battery vs a house battery in the truck, some vehicles have an electrical system where the alternator / starter battery voltage cycles up and down quite a bit while driving. Some of them drop down to less than 12 volts during the drive and can force off a battery to battery charger. This is definitely true on some vans but not others. Not sure about pick up trucks.

Not sure if I answered your question or not, so feel free to help me understand better.