8 replies to this topic

[Krist003]

Hello group,

I need some guidance from some of you electrical gurus. I recently purchased a 2004 four wheel camper (FWC) "Hawk" model. I am going through it and making worthwhile upgrades and have some questions regarding the 12V system.

Usage needs:
Right now I don't think I will wire the truck for the camper because I'm not sure if I really need it with my limited power needs. I will mostly use the camper for dry camping weekend trips (solo or with my young son) and maybe a once per year 5-7 day trip (we have a trailer for the major camping trips). Fridge is a 3-way so that will run off propane. That leaves the heater (not installed yet), lights, USB plugs and water pump. Limited use on all of those things except the heater through the night. I have a Honda inverter generator I can bring along with me as well if I really need to. The camper stays plugged-in in my garage when in storage so the battery will always be at full charge when I go.

Current Upgrades:
So far I have changed out the Elixir ELX-30 converter/power center to a Power Dynamics PD4135. It is a AC/DC distribution panel and power converter combo with smart charging. I also thought about replacing the Sure Power 1314A battery separator with a Blue Sea SI-ACR automatic charging relay/isolator (like FWC uses now), but I'm not sure if I will gain anything if I don't ever plug the camper into the truck.


Questions:

1: Is it silly not to plug the camper into the trucks battery system? I'm trying to keep it simple unless there is a worthwhile benefit to me.

2: Is the Blue Sea SI-ACR a worthwhile upgrade considering my needs? Or is it pointless if I don't ever plan to plug the camper into the trucks battery system?

3: Is it worthwhile to upgrade the battery cable size in the camper from the battery to the isolator? FWC uses 10awg at the factory, but I have some #6 if it will give any benefit. Will upsizing this short 6' run of cable help with charging when plugged into shore power? If I did end up wiring the truck for the camper, I would use 6awg as well.

4. If I upgrade the wire in the camper to #6, should I install a larger 12V circuit breaker at the battery for protection? It doesn't even have one currently. I believe 80A would be a match with the #6 wire?

5: If I upgrade the wire in the camper to #6, should I also upgrade the reverse polarity fuse in the new converter (it is currently a 40A fuse)? Assuming I'd leave that alone so it doesn't damage the converter.


I think that about covers it for now. Sorry for the lengthy post and thanks in advance for any guidance you can give!!! I really appreciate it.

[Vic Harder]

If you are not going to plug the camper into the truck, then the isolator is not involved in any way.  You could even remove it.  So, upgrading it is pointless.  

 

Likewise with the existing wiring.  Use it as is and note any potential issues.  Best thing is to have a good battery monitor so you can tell what's going on as you get used to your new camper and usage patterns.

[Krist003]

Sound advise, thanks. I will be taking it out next weekend and see what happens.

At a minimum, I may change the battery cables to #6 to see if that speeds up charging at all.

[pawleyk]

How are you currently charging the camper? I guess just from shore before your trips?

 

I'd connect to the truck at a minimum. It's easy and a good source of charging, assuming you use 6awg. At that point, an upgrade to the Blue Sea could be useful, AND the wire upgrade inside.

 

Like Vic said, if you're not hooking to the truck, no real reason to do any of that. 

 

KP

[Krist003]

That's correct, I keep it plugged in inside my garage between trips. Most trips will only be an hour or two away so that doesn't give it much charging time anyway. Maybe a couple 6+ hour trips per year. Its my first truck camper (I also have a travel trailer) so I guess I will have to see how things go and how I end up using it.

 

I will be upgrading the battery to a 100-125ah AGM and may add solar down the line, but for now I will use it and see what my power needs are. Thanks for the reply.

[ckent323]

Plan for the future.  I suspect you will want solar

I agree with Vic - if you do not have one, get a good battery monitor.  That is the place to start.  You can use it to keep from killing your battery as well as figure out your power needs for when the time comes to add alternative charging source (to shore power).  I like the Victron BVM-712 smart battery monitor (but the smart shunt may be adequate if you will always use your smart phone and you do not need the separate display, that will save you about $70).

Once you use the battery monitor you may find that you are routinely pulling your house battery down too far while out camping and not recharging from the truck or solar or shore power.   If you always camp in a place with shore power plug in or for whatever reason you don't pull your battery down while camping to levels that will significantly shorten its usable life then great, no need to connect to the truck or put in solar.

If or when the time comes I would think about adding a reasonably sized solar system before connecting to the truck.  Our solar system provides all our needs and we do not need to connect to the truck.   However, connecting to the truck may be the cheaper alternative but also more of a hassle (needing to periodically run the truck to recharge the house battery). 

Also, i agree with the others that there is no point in upgrading wiring until you decide on a house battery charging system to use when shore power) is not available. 

When that time comes to think about adding a charging system be sure to first figure out your typical power usage (using your battery monitor) and how long you will be running off your battery bank without truck or shore power.  Add some margin to whatever you come up with to account for situations of low sun, shade, etc.   After you know how much power you use, including any devices you want to add (e.g. 12 V fridge, whatever) then you can start figuring out the size of the charging (solar) system and the battery bank and the wiring.  Sizing the system and selecting the appropriate solar panel size is another whole topic (or how long you need to let your truck run to recharge if you decide against solar).

 

Craig

[Krist003]

Excellent post Craig, much appreciated. I have a Victron BVM-712 in my travel trailer. I guess I should probably pony up for one in the camper too. I like the idea of saving the money on just getting the smart shunt though, I’ll look into that.

I’m liking the solar idea. Any better options than the Renogy 100A starter kit?
https://smile.amazon...DKIKX0DER&psc=1

[Wandering Sagebrush]

Excellent post Craig, much appreciated. I have a Victron BVM-712 in my travel trailer. I guess I should probably pony up for one in the camper too. I like the idea of saving the money on just getting the smart shunt though, I’ll look into that.

I’m liking the solar idea. Any better options than the Renogy 100A starter kit?
https://smile.amazon...DKIKX0DER&psc=1

Maybe a larger panel would be nice, but you’ll know your ampre usage better than me.

[ckent323]

Krist003,

 

Use the amps per day spreadsheet (see the link on this forum) and figure out your worst case 24 hour electrical use (consider your electrical usage in all seasons that you camp in, i.e. spring, summer, fall, winter).

Now you know your daily consumption.  If you are planning to add a 12V refrigerator or something now is the time to add that additional consumption in.

 

Look at the Amp Hour rating of your battery and what type it is (Flooded Lead acid, AGM, Gel, Lithium).   You can safely discharge Lead Acid (FLA, AGM & GEL) to about 50% or rated capacity routinely without significantly reducing the life of the battery (see manufacturers specs for the details on your battery).  I prefer to use 60% because I am conservative and I rarely discharge below 75% full.

For a Lithium Ion battery you can routinely discharge down to about 80% (again see manufacturer recommendations for your battery).

Keep in mind that the main causes of premature battery failure are chronic overcharging and chronic undercharging (or frequently doing both)

Importantly: Lead Acid batteries (FLA, AGM Gel) need to be fully recharged after discharging before you begin discharging again.  If you routinely discharge a lead acid battery before fully recharging it you can shorten its usable life.   However, Lithium Ion batteries can be partially recharged before discharging again.  The important word here is routinely, occasionally or rarely not fully recharging or drawing down below 50% are not as big a problem.

Now you can calculate how often you need to recharge your battery bank.

Let's assume you consume 30 Ah a 24 hour day and your battery is a 100 Ah lead acid AGM.  The max you should routinely draw down your battery is about 50% (some argue you can go more - most of the manufacturer data I have read say the battery life will be shortened - you will have to decide what works for you).  So 100 Ah x 50% = 50 Ah   50 Ah - 30 Ah - 20 AH remaining.  That is not enough to get through a second day without fully recharging unless you cut back on power use or draw the battery below 50% full charge.

Now you have an idea of how often you need to recharge.  You need a minimum of 30 Ah each day (no margin) to fully recharge your battery before discharging again the next day.   You can get that from idling your truck for around a half hour or so depending on the size of your alternator and wiring or you can get it from Solar power or shore power (generator, plug in whatever).

If you go solar you should think about the fact that solar panels are rated at perfect alignment to full sun.  So a 100 Watt panel only puts out 100 W on a clear day, near mid day with the panel exactly perpendicular to the sun (if it sits flat on the roof of your camper it will never be perfectly aligned unless you park an a slope.)   

Also, any shade (even tiny amounts) will reduce the output of the panel, cloudy, foggy, rainy days also result in low panel output.  So the solar system design needs to account for these issues by derating the expected output of the panel.  Some use 50% I prefer to use 80% - 100%, again because I am conservative, I like having margin and larger panels are only marginally more expensive than smaller panels.

So how big of a panel do you need for those 30 amp hours (30 amps for one hour or 3 amps for 10 hours).  Just ballparking an estimate, a typical 100 Watt panel puts out about 7 AH at best (perfectly aligned, clear day, full sun, midday).  Derating 50% yields 3.5 amps.  So a 100 Watt panel might work if you could average 3 amps per hour for 10 hours.   In the middle of summer you might get 8 hours of good charging in much of the continental US perhaps a bit more the farther North you go.  In spring Fall and winter you will likely get less than 8 hours of good charging.  However, considering the possibility of morning and or afternoon shading, clouds, etc I would suggest using 200 watts as the minimum system size.  That will give you some margin.

I have found that larger panels are similar in size and weight to smaller panels with the price less than double for double the wattage.  Therefore I recommend getting the largest panel that will fit on your camper.  

Folks will argue that they do fine with 100 watts.  the question I have is if they are actually fully recharging their battery (assuming lead acid) before discharging again.  I have read about a number of people with solar systems having to replace batteries after 4 or 5 years when a deep cycle AGM battery appropriately recharged should last around 10 years or more.

I have two 220 watt 6v AGM deep cycle batteries in our camper.  That give us 110 AH of usable power at 12V.  (Note: I bought these batteries in May 2017 and they are still doing excellent however if I were buying batteries now I would think hard about Lithium Ion).  We camp year around and use upwards of 40 - 45 Ah a day worst case, worst season.  Also we sometimes are in one place for up to a week at a time and often we deal with shade, clouds, fog etc.  We found 200 watts was not quite enough.

I upgraded my solar system a year ago to a single 360 watt residential panel which when mounted on the roof of my camper actually weighs about 2 - 3 pounds less (counting cabling and mounts) than the two 100 watt panels it replaced.  The 100 watt panels cost me about $110 each.  The 360 watt panel cost me $310.  I had to upgrade my Solar controller from a Victron 75/15 to a 100/30 but after an 82 day trip to Alaska, Canada, Montana, Iowa and back to California between August 6 an late October 2021 we found we had plenty of recharging capacity from the new bigger panel.  I wanted a 400 Watt or larger panel but the local distributor did not have one at the time.

I hope this is of some help.  Vic Harder has written a pretty good post on selecting and sizing a solar system at the following link:

https://www.wanderth...wer#entry247442

Edited by ckent323, 01 April 2022 - 12:06 AM.