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So, you want to setup a good electrical system in your camper?


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#1 Vic Harder

Vic Harder

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Posted 01 February 2021 - 03:12 AM

So you have a camper shell… or are wanting to start all over with wiring up your camper?  This guide/thread should help.  Technical explanations and even terms like “current” “voltage” and “watts” are not used unless absolutely necessary.

 

If you have questions or comments, please post them in this other thread instead of here, to keep this one cleaner and easier to read.

 

Questions regarding "So, you want to setup a good electrical system in your camper?" - Electrical, Charging, Solar, Batteries and Generators - Wander the West

 

 

Charging your camper from the truck?

The wiring that comes with your truck for a trailer connection is too thin to carry enough power back to your camper batteries to do much good.  That includes wiring that your camper installer may have put in when you picked up your brand new camper.  This needs to be upgraded to at least 6AWG wire.  Copper wire is expensive these days!  The wire should also be rated to handle automotive (read: greasy and hot/cold).  I use 2AWG welding cables in my builds.

 

This wire goes from the engine bay, under the truck and back to the truck’s box or flatbed tray to a heavy duty “Anderson Power Pole” connector.  Be careful when you route the wires/cables to make sure they don’t rub or interfere with anything.  When going through metal surfaces, ensure you protect the cable from any sharp edges.

 

You need two cables, one for the positive wire, and another for the ground.  Using a “frame” ground is not recommended.  The positive wire leaving the battery has to immediately go to a fuse/breaker to protect the wire (and you) in case it gets shorted somehow.  I use 100A Blue Sea 285 breakers.  Its nice to have a breaker (vs a fuse) that you can use as a “switch” to disable the alternator charging function or to remove power during maintenance work.

 

You will also want to make a new hole or two in the wooden “floor pack” part of your camper and route the wires into the battery box of the camper.  I used a ½” drill, and sealed it with a urethane caulk.  Butyl rubber tape works well as a sealer too.

 

Just before these hefty cables connect to your camper batter(ies), you will want to add another 100A breaker to the positive wire.  This way the cable is protected on both ends.  From there a short run from the breaker to the positive battery wire completes the basic circuit.

 

You may wonder why a fuse or circuit breaker is needed at each end of the main battery charging positive cable.  Isn't one good enough?  Good question!  (and thanks to Jon R for suggesting that I answer this question here) 

 

That heavy duty wire can carry a lot of juice.  And it is getting that juice (power, aka current and voltage) from BOTH batteries.  Meaning that if any part of that wire touches a metal part of the camper or truck, all the available power in those batteries is going to come out of that wire and create a LOT of sparks and heat and more than likely burn down your camper & truck.  And if you are unlucky enough to be part of the circuit that the current goes through, it could kill you.  It's only 12V you say?  Yes, and people have been known to weld with 12V out on 4x4 trails.  Do you really want to experiment with that unexpectedly?

 

Having just one fuse/breaker at one end still leaves the other battery connected to that wire.  So, it just makes sense to have one at either end, as close to the batteries as possible.

 

OK, two breakers, got it.... (I hope!)  Now the camper/truck batteries are linked, unless you trip one of the breakers manually, and the truck will charge the camper battery if it running and the camper will charge the truck battery if you have solar and the sun is shining.   Cool, eh?  (yes, I’m Canadian!)

 

Variations

If you do not want to charge the truck from the camper (via solar for example) and the charging function will only ever flow from truck to camper, then you might want to add a DC-DC charger into the mix.  I say might, because an older truck with a “dumb” alternator will now happily charge your camper batteries.  My truck is a 2006 Chevy 1 ton, and I can saw 90A going over the wires (I have a gauge for that) into the AGM batteries in my first FWC.  That’s lots.. like over 1200W!  That usually ramped down very fast (10 minutes) to more like 40A for the duration of the charging time.

 

BUT, now that I have LiFePo4 batteries, they have a different reaction to charge current, and will take whatever my alternator can through at them.  I was afraid that my alternator would burn up.  So I added a DC-DC charger to LIMIT the charging current to a nice stable 30A.  I’ve used both the Renogy and Victron brands.  The Victron is smaller, but runs quite hot.  I added a cooling fan to keep it happy.

On the other hand, if you have a truck with a “Smart” alternator (almost all have those now) they tend to “manage” themselves and reduce how much power they put out, in order to reduce the load on the engine, and thus improve fuel economy.  As smart alternator will not charge your camper batteries much at all with the stock trailer plug sized wires, and likely not much more with 2g wire.  In this case, a DC-DC charger will make sure you do get a decent amount (30A) of charge whenever the truck is running.

 

The DC-DC charger goes between the 100A breaker in the camper and the camper battery.  It will likely not fit into an already full camper battery box, so you need to find a well ventilated spot for it nearby.  The closer the better.

 

If you want to charge the truck from the camper, then you can’t use the DC-DC charger wired like this.  Instead, you will want to use an Automatic Charge Relay (ACR).  I use the Blue Sea ML-7622.  It is robust enough I could actually start my truck with the camper batteries if necessary.  This relay can sit anywhere in the circuit between the truck and camper, as it automatically senses the presence of enough power on either side of the ACR to connect the two systems together.  Meaning, if the sun is shining on your solar panels, you are charging both the camper and the truck.  Or, if driving, the alternator is also charging both the truck and the camper.

 

More later ...


Edited by Vic Harder, 20 August 2021 - 04:10 AM.

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#2 Vic Harder

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Posted 02 February 2021 - 01:39 AM

How much battery power do I need?

A lot of this section was detailed in my other thread – I need more power Scotty! – but… figuring out how many solar panels and how much battery capacity you need depends on knowing how much you will use.  It is surprisingly similar to knowing how much water to take on a trip:

  • How much will you use in a day?
    • Doing what?
    • Washing
    • Drinking
    • Showering
    • Cooking
    • Etc.
  • How many days do you want to stay out before refilling your tanks?
  • Multiply days by daily usage and you know about how big a water tank you need. 

The same concepts apply to your battery size:

  • How much will you use in a day?
    • Doing what?
    • Running the fridge
    • Heating the camper
    • Circulating air with the fan
    • Lights
    • Charging portable devices
    • Running a radio or two
    • Etc.
  • How many days do you want to stay out before recharging?
  • Multiply days by daily usage and you know about how big a battery you need.

For example, these are my estimates for figuring out how much battery I needed for my Hawk camper:

  • 130L fridge.  It uses 3 amps when running.  Figure it will run 30% of the time or less.  That’s about 8 hours a day.  3A times 8hours = 24AH.  Amp Hours (AH) is how battery capacities are measured.
  • Fantastic fan.  It uses 1.5A when running. Figure on running it no more than 3 hours (evening and overnight).  1.5A times 3H = 4.5AH.
  • Propex Furnace.  It uses 1.4A when running.  Figure on about the same 8 hours on a cold night = 11AH
  • Note to self:  I am unlikely to run both the fan and the furnace at the same time…
  • LED lights.  Not much, about .8A.  Not much use here as we rarely camp during long winter (dark) hours, so maybe 4 hours = 3.2AH
  • Water Pump.  3.5A for less than an hour a day, more like 30 mins = 1.75AH
  • Inverter/USB plugs.  This really depends on what you are bringing.  I run a laptop, 2 phones, a cell phone booster, camera, flashlights and more.   All that uses about 6A for no more than 6 hours a day = 36AH.
  • Total all those loads up and we get 24+4.5+3.2+1.75 = 34AH without the portable office stuff, 70AH with it.

This means that I need at least 36AH of usable capacity to stay out 1 day without charging if I am not using the portable office, 70AH if I am.

 

The key word there is usable.  Lithium (LiFePo4) batteries give you almost 100% of their rated capacity in usable power.  Lead acid (Absorbent Glass Mat – aka AGM and Flooded Lead Acid – aka FLA) about 50%. 

 

So if your camper came with the 75AH battery that was common a few years ago, you have 75/2 = 37AH of usable capacity.  In plain English, you use all your battery power in just ONE DAY.  Using it over the weekend, thinking you can recharge when you get home means that the batteries are run almost to 0%, which severely limits the battery’s life.

 

On the other hand, a single 100AH LiFePo4 battery could be used for a whole weekend and still be at around 30% capacity, which it will tolerate for many thousands of weekends.

 

But what if I want to stay out for many days or even weeks?  Let’s save that for next time…..


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#3 Vic Harder

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Posted 02 February 2021 - 06:16 AM

How to recharge your batteries for multi-day trips

 

There are essentially three different ways to recharge our batteries:

1) Off of the truck engine

2) Solar power

3) Shore Power.

 

Charging from the truck: We’ve already started talking about this, when we covered charging off of the engine in the first post. Basically, to do a good job of this you need:

- Upgraded wiring to 4AWG or thicker

- Install breakers at both ends

- Join to the camper with Anderson Power Pole connectors

- Link the two systems with either a DC-DC charger or an ACR.

 

Shore Power: Let’s talk about this.

Really, I only use shore power at home when I have the camper off of the truck. Other folks may camp more often in campgrounds where shore power is available.

 

If your camper came with shore power wired in, there a plug on the outside of the camper to plug in an extension cord. Campground power can be iffy… meaning questionably or inadequately wired, so some form of protection from that “iffy” power is a good idea. This protection is in the form of a “surge protector” or “EMS” and vary in price from $100 to $300. Those $100 surge protectors protect against some risks and are usually good enough when you know the wiring is good… like at home when you plug your computer into a surge protecting power bar. But in a campground, the odds of the wiring being “good” are … well, not worth the risk. A good EMS is a better idea. This one from Progressive Industries is good.

 

For more on this topic, check out this LINK

 

OK, so once the AC 120V power comes into your camper, it goes through a breaker, and from there to an AC socket, maybe the fridge, and to a Battery Charger. FWC/ATC have been using the IOTA brand for ages, and it is a decent product.

 

Do I need all that when wiring my own?

 

I didn’t so I wired mine differently. I mostly boondock, and to keep things simpler I did not install a shore powered AC plug or breaker. Instead, I wired the plug on the outside directly to a Victron AC/DC charger and don’t have any AC plugs that are powered via shore power. Mine are powered from a 3000W inverter so I can run my induction cooktop, but more on that later.

 

The minimum you need for shore power is a way to charge your battery so you can keep using it the next day, and the day after and so on. This would be similar to having the truck/camper in your yard/garage and plugging it into recharge it using a portable battery charger. The sizing of the charger and how programmable it is, are two key factors to consider. For example, can you program the settings in the charger to accommodate your battery’s chemistry? AGM, FLA, or LiFePo4? Some models of the IOTA units have interchangeable “dongles” that alter the programming of the unit as needed. I like the Victron series of chargers, since they are not only fully programmable, but also communicate via Bluetooth to my phone, so I can see what’s going on.

 

Sizing is the other major consideration. You will want the charger to put out enough power to be able to keep up with the loads you have, and then some, so that it can actually charge the battery overnight. That means it has to have enough “juice” to put out about 2x your daily load… 1x for the actual load, and another 1x to replace the draw down from the previous day.

 

Using the example from above where we pulled 37AH out on a typical day, we need to be able to put out 2x that in a 12 hour period. 37*2= 74 all divided by 12 = 6A. So you need a 6A charger, which is not all that robust. The IOTA puts our 30A for example.

 

So with just a battery charger like the IOTA or Victron, you can recharge your batteries while using shore power. Wait, how do even know when the batteries are fully charged? Let’s discuss that next time….


Edited by Vic Harder, 03 February 2021 - 10:53 PM.

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#4 Vic Harder

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Posted 02 February 2021 - 06:16 AM

How do I keep my batteries healthy?

Most of us are looking at AGM or LiFePo4 batteries these days, so I will not be addressing FLA (flooded lead acid) batteries, even though they are the cheapest of the bunch right now, and available in large sizes (think golf carts).

Both types:

  1. Are “sealed” meaning that they don’t really need much venting, if any at all
  2. Prefer to be used at room temperature
  3. Don’t love temperature extremes
  4. Can not be monitored easily simply with voltage measurements.

Yes, you can find charts that tell you what the State of Charge (SoC) is of a battery is, but those are resting voltages.  Resting voltage means that there has been no load or charge on the battery for several hours, and the batteries are at room temperature.  This rarely occurs during active usage, which is when we really need to know the SOC. 

 

For example, it is said that an AGM battery is at 50% SOC at 12.2V, fully charged at 13.00V and at 10% SoC at 11.51V.  Now take a fully charged AGM and subject it to a heavy load, say an Induction Cooktop, which will pull out almost 150A when on high.  During such a test, the battery voltage may drop to below 11V and you could think the battery is no good or nearly dead.  Turn off the Induction cooktop and wait a few minutes, and it might be right back up to 13.9V.  So, it is discharged or not?  Is it overcharged?  What caused it to be so high after?  Oh, right the sun is shining now…. So what IS the actual SoC?  You have no idea based on the voltage!

 

My conclusion is that measuring voltage to determine battery health is not practical for a camper in use.

 

And don’t get me started on the “idiot lights” that come with some campers.  Those are terribly misleading and ALSO USE VOLTAGE to determine which light to turn on. 

 

What does work?

A shunt based meter.  A shunt, is a super accurate measuring device that is designed to measure the amount of current flowing through it.  Because it measures is all, it can determine how much is left in the battery.  I am fond of the Victron BMV series of meters, but there are also some inexpensive knock-offs that are reputed to work well too.

 

Be aware that there are some SoC meters which are not shunt based, but guess at SoC based on voltage levels.  These are worse than idiot lights, because we think they are more accurate because they give us a number.  They can’t be accurate, any more than a voltage reading can be.

 

How does a SoC meter help me keep my batteries healthy?

We covered some of this earlier, and to recap, all batteries are rated to last a given number of “cycles”.  A cycle is going from a fully charged to discharged to fully charged state again.  The level or depth of discharge determines how many such cycles that battery can survive.

 

As stated above, AGM batteries are often said to be safe to discharge to 50%.  This is a compromise, meant to provide a “reasonable” lifespan for the battery.  That said, if you need to discharge it to 80% because you got caught out and unable to return, then the battery won’t suffer too much.  Even if you routinely discharge it to 90%, you will still get 500 cycles out of the battery.  That could represent 500 nights of camping!

 

So why do we hear about batteries only lasting a year or three?  Because a deeply discharged AGM battery can easily freeze if subjected to cold weather, and that will kill it.  If you intend to discharge your AGM battery regularly, at least keep it warm.

 

In contrast, LiFePo4 batteries will last thousands of cycles when taken to 10% SoC.  That’s more than most of us will ever do in our campers.

 

More to come…


Edited by Vic Harder, 09 February 2021 - 03:00 AM.

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#5 Vic Harder

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Posted 02 February 2021 - 06:16 AM

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#6 Vic Harder

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Posted 02 February 2021 - 06:16 AM

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#7 Vic Harder

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Posted 02 February 2021 - 06:19 AM

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#8 Vic Harder

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Posted 02 February 2021 - 06:19 AM

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#9 Vic Harder

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Posted 02 February 2021 - 06:19 AM

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#10 Vic Harder

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Posted 02 February 2021 - 06:19 AM

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