I hope this thread will help us gather most of the info out there on powering our campers into one place.
In short, I hope it will address how much power we need, and how to reliably get it.
To start with, I want to acknowledge the work of others in this space. Forgive me if I miss a few, and please do point them out:
HandyBobSolar - http://www.w8ji.com/...ging_system.htm
Hawk Solar Upgrade - LINK
Running heavier wire for solar panels - LINK
Rice Build - LINK
DrJ on DIY Solar/Trimetric - LINK
ACR – improving your battery isolator - LINK
Modeling Small Solar installations – CarlD - LINK
How much power do I need?
The first bit we need to look at is how much power is needed. DrJ LINK indicates about 60 AH/day is typical for FWC use. If you want to run the numbers yourself:
This calculator can confirm some of that, although it is designed for home alternative energy use - LINK
I went at this in some detail, reviewing each of the appliances I intend to use, which are:
TruckFridge 130L – 24w/hr, 60w input, 5 A; 53 lbs; Size - H x W x D 29 ½" h x 20 ¼" w x 20 ¾" d (estimate 14hrs/day at 24w/hr)
Shurflo 4009-101-A32 pump 12vdc @ 3.5A (max) = 42W/hr (estimate 2hr/day)
ProPex 2200 heater – 1.4A = 16.8W/hr (estimate 5hr/day)
LED lights total = 1A (estimate 6hr/day)
Overhead lights = .8A
(Flood lights = 2.8A)
Porch Light = .2A
Fantastic Fan = 1.5A at full speed (.2A at low) (estimate at 4 hrs/day)
USB chargers (negligible?)
Inverter (120 v to 12v) (estimate running small one of 50W for 2 hrs day)
- Camera battery charger
- MS Surface 3 Pro laptop
Total of 60 AH/day. That’s exactly what DrJ figured out for himself, and also worst case. For example, the if the heater needs to run for 5 hrs a day, then it is likely cold out and the fridge won’t be running for 14 hrs, and vice versa, meaning my draw could be as little as 53Ah, assuming no furnace is needed on warm day.
How much battery do I need to support this load?
And you can use this to figure out your battery bank size
This Crown website has lots of good sizing info too: http://american-batt...olar-batteries/
To put it in words, Crown and others suggest no more than 30% of discharge for maximum battery life for Flooded Lead Acid (FLA) batteries, while 50% is possible with Absorbent Glass Mat (AGM) batteries, but that will reduce the battery life. Plugging in the numbers to the capacity calculator (LINK), or spelling it out like this for my case:
60 AH * 50% and 2 days = 240 AH. That means I need at least a 240 AH battery as the smallest I can get away with. If I want to have 3 days between charges, even at the maximum 50% drain the number is 360 AH. Hmmm, maybe I need to adjust my expectations.
OK, so let’s go for 2 days between charges, but keep the batteries healthier, allowing only a 40% draw... that yields a need for 300AH of total capacity. OK, let’s run with that.
Crown’s 6CRV330 model battery looks like a good fit here. Fit being AH. Size is another matter... it is 14.6” tall. I will have to design my battery box to fit that.
Now here is a really strange thing. A bigger battery (or a lower load) get you more AH of daily use and a longer life per battery than you might expect. The relationship is non-linear. Lowering your AH draw or stuffing in more battery will lead to better than expected battery life. This is reflected in the warranty on batteries, which is often stated as 2/5 years. Two years of hard use, or 5 of gentle use. Draining them 50% every day, or just 30% every day.
What kind of batteries should I get?
OK, so more battery is better. What kind? FLA or AGM?
Apparently you can tilt the FLA up to 45*. That would be significant pucker for me, so that isn’t really a limitation.
AGM batteries are spill proof. You can even mount them sideways. That could open up some interesting mounting options in a FWC.
AGM’s can be charged up to 5x faster than flooded lead acid types.
AGM’s can also handle vibration, because they were designed for military aircraft and the shaking they go through, so wash board roads should be no problem.
FLA batteries need maintenance. Lots of it, to stay healthy, whereas AGM’s need none.
Finally, FLA batteries are about 50% of the cost of AGM’s.
OK, so cost favors FLA; everything else favors AGM - vibration, charge time, zero maintenance. AGM it is. How to charge them up?
How do the batteries want to be charged? There are right and wrong ways to charge AGM batteries. Battery capacity and life are critically impacted by how they are charged. Guys like HandyBob are very passionate about the fact than almost NOBODY does it right, and that almost ALL batteries in campers are chronically under charged.
Let’s not be part of that crowd!
First off, there are 3 different types or stages of charging an AGM battery:
Bulk (when you can dump practically unlimited amps into the battery at a pretty high voltage)
Absorb (when the battery is about 85% full, and it gets harder to “push” the amps into the battery)
Float (when the battery is basically fully charged and you want to keep in there)
Manufacturers list a lot more parameters about their FLA batteries than they do for their AGM batteries. I suppose the FLA batteries need more maintenance, so that makes some sense. So , I had to do a bit of digging for this info:
Rolls/Surrette says the max charge rate, or bulk rate, is c20 * 0.35, but more typically c20 * 0.25 - LINK
What does that mean? The c20 rate is how many Amps the battery can provide before it is completely dead after 20 hours of use. If you want more on AH ratings, go here - LINK. The c20 rate is the most commonly quoted one, so my chosen 330 AH battery just happens to have a c20 rate of 330 AH. Running the numbers, I get 330 * 0.25 = 83 Amps, and 330 * 0.35 = 115 amps. These are the amps these batteries want to see while charging. Whoa.... that’s a lot of juice.
More importantly, our AGM batteries have a minimum charging current, that being C20 *0.10 = 33A for my 330 AH Crown batteries - LINK
So, now we know that we don’t really want to draw more than 30% of (c20) AH capacity, but can go to 50% in worst case settings. And we want to charge at least 10% of C20 (330AH) = 33A, and can go up to 115A during the bulk charge phase.
How to do this? A FWC will usually have three options – the truck’s alternator, shore power and Solar. And we introduce another factor here besides the charging current, namely the VOLTAGE at which the battery is charged. This is really important stuff. Read on below, but before getting to charging, let’s look at measuring your batteries STATE of CHARGE (SOC)
How do I know what the SOC is of my batteries?
I think many folks have already sung the praises of the Trimetric 2013 Monitor. I think the simple answer to this question is get one of these. Done. As for why, this POST is very relevant – showing essentially that many folks measure their battery SOC when there is no load on it. That’s a sure way to kill your batteries. Apparently you need to measure the battery under load. The last two pictures on this post are perhaps the most important. The meter shows the battery at 12.1v when at a 49% SOC – the lowest you should ever take an AGM battery. Disconnect the load, and it bounces back to 12.32V, or 70% SOC. If you think you still have 70% left in that battery, you will be majorly disappointed in the battery life/performance you get out of it.
Even this site that has this handy table is mistakenly calling this a no-load table. The marine folks above think it should be considered a full load table.
Oye, sometimes this stuff makes my head hurt!
Charging via your truck’s alternator
Since we are looking at alternators first, let’s consider what the manufacturer (Optima 75 AH Yellow Top) of my truck’s starting battery has to say about how it should be charged. LINK.
They say it wants from 13.65 up to 15V (up to 15.6 if you can monitor the battery temp), at unlimited amps for the bulk charge, or 13.8 to 15v via a charger for 10 hours for an absorb charge, and 13.2 to 13.8 for float charge. The min/max amps for optimal charging (c10 and c35) are 7.7A and 30A.
When your truck is running at more than idle it is outputting its nominal alternator rating. My truck has a 135A alternator. Thanks to the car audio SPL wars, many higher power alternators are now available, and I can upgrade that if need to. These guys make BIG alternators LINK
Assuming my Optima Yellow top starting battery is fully drained, my stereo and headlights are on, the draw would be:
Battery = 30A
Stereo (500w amp plus head unit) = 35A
Low beam 2 x 35w bi-Xenon Headlights = 5A
Misc small lights = (10 x 10w each) = 7A
So I have 77A being taken by the truck, leaving 58A for the camper batteries.
To get better charging rates, I can turn off the stereo and headlights. Assuming I do that and can get the max charge amps out of my alternator, the other key factor to consider is the voltage at the camper battery. As we saw for the starting battery, AGM batteries want different voltages depending on where they are in their charge cycle. Assuming for just a second that the alternator can deliver these, Crown says that this is what you want for a 12 volt system (which includes 2x 6v batteries in series):
Bulk v = 15
Absorb v = 14.52
Float v= 13.5
Note: Trojan lists an alternate value of 14.4v for absorption charge. http://www.trojanbat...ry-maintenance/
Anything less than these voltages and the batteries will not charge properly. They will work, they will take some charge, but they won’t be at full charge, and will drain faster and ultimately fail completely well before their time.
So we need to get those volts to the camper battery, which means we really need to consider the voltage drop that arises from the resistance in the cabling/wires between the source of the power (alternator) and the batteries. Voltage drop depends on the specific length and gauge of the wire, for a given current drawn across it.
So, back to my 330AH batteries. As we saw, they want between c10 and c35 during the bulk charge phase, at 15V.
OK, so can I even get 15V from my alternator? I just went out and measured my alternator’s voltage output. To do that, I measured the battery when the truck was not running (11.5v – whoa, that’s pretty discharged, and that after normal short runs for groceries and such... seems like maybe I need to hook up my trickle charger!). This low state of charge for the starting battery is great for our testing purposes, as it means the alternator will be in bulk charge mode when I start up the truck. So, I start it up and Woot!!! I see 15.2V! Remember that Optima says they can take up to 15.6 for short while during this phase.
Now, what do I need to do to get at least 15V of those volts to my camper batteries, with at least c10 levels of current, as per Crown’s recommendation?
I will be hooking up the wires to my alternator (not the battery posts) and I figure that the distance will be 20’ from there to my camper batteries. This includes all the short little sections between the breakers, the ACR and such. I will want less than 0.2v of loss, or around 1% so I get the full 15V at the camper battery.
Let’s see what the stock – as supplied by FWC – wiring will get us. Using this calculator LINK, and assuming:
10 AWG (stock FWC wire)
15.2 VDC from my alternator
With a SET of wires this size (no frame ground)
And 33A (c10) minimum for bulk charging
(pic didn't come through)
It looks like I will get 13.88v at my batteries. That’s an 8.7% voltage drop, or 1.32v. That only gets me to slightly above a float charge level, not absorb, never mind bulk level. Clearly, those folks on this forum who have upgraded their wiring from the truck to camper and gotten better results are on to something.
What if I want to get closer to a c25 level of current for my bulk charge? That’s 25% of 330AH = 82.5A. Aside from melting my wires, that would result in a 21.7% voltage drop and only 11.9v getting to the camper batteries. Ouch.
BTW, use this link to figure out your fuse size for a given AWG, so you don’t melt your wires! - LINK
So, what AWG wire SHOULD I use? You can use this calculator from Blue Sea (Link), although it generalizes the voltage values too much. I prefer to use the original calculator I linked to and use trial and error with the numbers to figure this out
I figure I should be running 1/0 AWG. That will get me 15V with 50A:
(pic didn't come through)
Let’s think about the implications of this for a minute.
First, I’ve seen a few folks here upgrade to 4AWG, which isn’t big enough according to our calculations, and yet it seems to work for them. Why?
Well, for one thing, they are using smaller batteries. 220 AH or smaller. C10 for those batteries is only 22A. Using the calculator and changing the wire size to 4AWG, I get 14.98V at 22A to the camper batteries. That’s enough to get us well above “absorb” charge state and good enough for a bulk charge even. Given enough time, that will charge up your camper batteries.
How much time? Going back to the Optima website, they recommend 13.8 to 15v for up to 12 hours for a 75AH battery. For the 220 AH battery we just ran the calculator for, that means 220/75 * 12hrs = 35.2 hours to fully charge that 220AH battery. Oh, and if your starting battery is low too, then you have to factor that in too = 295/75 * 12 = 47.2 hours! That’s a lot of driving! And if you need to charge your battery daily... well, last I checked there are only 24 hours in a day. Ooops.
Maybe this is why my nice new Optima only read 12.0 v this afternoon when I tested it. The trickle charger goes on NOW.... stay tuned for results on that. OK, after charging for 18 hours at 10A and 15v the battery reads 13.0 v this morning. Much better. How much better?
According to this graph, at 12v I was at 20% of charge before. Darn near dead. Now, at 13 v (my analog meter needs to be replaced!) I am at 100% charge.
A quote from HandyBobSolar’s website might be appropriate here:
“Get the battery manufacturer’s charging specifications and pay strict attention to them. The charger manufacturers are nearly all not setting their equipment up for the voltage that the battery manufacturers specify. The difference between 14.4 & 14.8 volts is not 3%. That difference is nearly 20% of the charging range (12.2 to 14.8 volts). That 20% makes a huge difference in how full the battery gets before the charger shuts off. You can eventually get the batteries full by charging at 14.4 volts, but it takes hours, not minutes. We have related industries that are not talking to each other and the outcome is that the majority of RV’s are running around with weak batteries.”(emphasis added)
In short, without some other charging method, your truck will never keep the camper batteries (or the starter battery for that matter) at full charge.
See this LINK for a good write up about how to check your vehicle battery and alternator.
Another implication – and a quick note about battery isolator/charge relays:
Many folks have noticed that the battery isolator prevents their alternators from charging the camper batteries. Upgrading the wiring and/or using a BlueSea ACR seems to help. Why?
The isolator is designed to protect the truck starting system so you don’t get stranded with a dead starting battery. It monitors the camper battery, and if it is TOO low, won’t connect to it. What voltage is that? 12.4v. So let’s imagine that your camper batteries are actually at 14.5 volts and would benefit from a long absorb charge cycle, and they want 20 amps for this purpose (about right for a 100 to 200 AH battery). The wire feeding the isolator is the same one running to your batteries, and 20’ long or so.
The ACR will sense that it can charge the camper battery (sense voltage implies no current movement). So it connects. Current starts to flow across that FWC stock install 10 AWG wire. As soon as it does, it incurs voltage drop from trying to stuff all those electrons through that tiny wire. The voltage it now sees is only 13.7v. So it disconnects. After a bit, it notices the batteries are back to 14.5 and connects again... click, click, click.... and no charging is really happening. Sound familiar?
Bigger wire is the answer.
Folks, there is only bad new here, as the voltage output cannot be easily adjusted to meet manufacturers requirements. Even so, a lot of members here have the IOTA DLS-30 with IQ4 as their charger. There is a lot of discussion about the Iota DLS series and IQ4 on the net. The unit is frankly no good at all for FLA batteries – see post #32 in this thread: https://www.solarpan...a-charger/page3.
That said, it might work for AGM batteries with the IQ4, which also appears to be conservatively set, with bulk/absorb only 14.8v (should be 15) and float at 14.2 (should be 14.52).
If you are willing to forgo the automatic features of the IQ4, you can use a trim pot inside the DLS-30 to tweak the output voltages, and use the two separate output voltages to manually do (enabled via the Two-Step Voltage Jack) bulk and float charging. But you have to be careful, or you will boil your batteries to death. Iota DLS manual here http://www.iotaengin...lib/dlsmanl.pdf and the IQ4 manual here: http://www.iotaengin.../#/products/iq4
Info on the trim pot in this thread - http://forum.solar-e...r-potentiometer
My understanding is that when you adjust the higher voltage – to say 15v from 14.8, the normal output voltage will also go up .2v, to 13.6. This would give you a good two stage charger, for bulk and float levels. I don’t know what happens if you adjust the voltage up to 15v and then plug in the IQ4. IDEALLY, it would stay at 15 for bulk, and scale the other voltages too. I will have to try that, or maybe someone who already has a DLS30 and IQ4 wants to try this (at their own risk)?
Conclusions re Alternator and Shore Power
My conclusions about shore power are the same as those reached by HandyBob, who says “Therefore, you can’t expect your converter to charge [your batteries], either. You are actually lucky to ever get your batteries over 80% full with a converter that is plugged in for several days unless the rig is stored and no electricity is being used.”
Oh, and a generator makes no difference here either. If you are feeding your batteries through the DLS30/IQ4 you would have to run the generator for several days also.
There is just no way around it. You have to get the charge voltage up to 15v to get into that bulk charge state, and then once that is done keep it at absorb for many hours to get the last 15% of charge done before you go to float charging. Shore power through an IOTA unit won’t do it if you are using your camper while attempting to charge it, it just can’t keep up. And we don’t have enough hours in a day to drive enough to charge fully via the alternator either.
That said, if I was to camp for two days in the winter in Banff NP, and no charging took place, I could get away with my 330AH setup. My batteries would be down 38%. That’s acceptable. They would get partially charged on the 2 hour drive home from the park, and then the IOTA with IQ4 would likely get them up to a full charge during the week before I headed out again. Boon docking is another story...
In short, we need properly set up solar when boon docking. And what does that look like?
How many AH do I need to recover?
You want enough solar power to recharge your batteries to full power after the number of days you decided (above) would be how long you will go between charging. In my case, that was 2 days, bringing my 330 AH batteries down to 40% to a 60% SOC. Now, on the third day, the sun is out and I need to recharge my batteries, and provide enough power to supply my daily needs to I don’t continue discharging my batteries. Basically, I need to have enough power coming from my solar panels to run my daily load with enough left over for the battery charging.
That’s 60 AH plus 330*40% = 60 + 132 = 192AH.
Sizing your solar panels
You need to know how many solar hours you have in a day at the location where you are camped. This map gives you a good idea - LINK. I myself will often be in zone 5, sometimes in zone 3. That’s between 4.2 to 5 hours a day, at solstice. In the winter, that can be up to 50% less! Winter also adds snow cover considerations. Right now I am not planning to camp in winter, so I’m just going to go there right now. And to keep it simple I’m going to estimate 4 hours of solar a day for my three season camping.
192AH needed with only 4 solar hours available means I need to generate 194/4 = 48.5A when the sun is shining, worst case.
Best case, my system never gets that loaded down, and I just need 60AH every day to keep up with my consumption = 60/4 = 15A
I suppose it would make sense to assume that a typical scenario would be to go 1 day without sun, and then have sun to do a recharge. That means 120/4 = 30A are needed every other day during my available sunlight.
The size of solar panels is usually given in watts. Watts = volts * amps. I would use 15v for the voltage number to make sure I get the needed voltage to bulk charge the batteries, so the watts needed are 30*15 = 450.
OK, so I will need two 225w panels. I think I will mount one on the roof and use another in a portable setup. And I will want to use 24v panels to keep the size of cables down. Why? Well, I understand that the wires to the roof are about 10’ long, and that the stock FWC is something like 12 or 10 AWG, depending on the vintage of the camper. I think mine has 12AWG.
Let’s say I put 3 of the 100W GrapeSolar panels from HomeDepot on the roof. I would be trying to feed 16.68A at 18v back to the controller. Plugging that into the voltage drop calculator (LINK) I get 17.47v, a 2.94% loss. If I use a 265W Canadian Solar 24v panel, I will be trying to move only 8.66A but at 30.6v to the solar controller. That yields 30.32v, a 0.92% loss. Much better. To get the equivalent efficiency from a 12V panel I would need to upgrade the wiring in my FWC to 6AWG, and that is not easy to do.
It gets even more important when considering the portable panel voltage drops, as the wires are much longer to this panel. I figure that panel will be 50’ or more away from my camper to catch the sun while I am parked in the shade. Using the commonly suggested 8 AWG wire over 50’ yields a 5.83% loss with that 12v GrapeSolar panel, and only 1.76% with the 24v panel.
24v seems like a no-brainer to me, except that I can’t use the highly recommended Trimetric 2030 charge controller, and have to get a MPPT type instead. The cost difference is substantial ($300 or more).
I’ve put together a spreadsheet of my costs for this solar setup, and the number is a bit scary, actually. So I am hoping someone can point out that I made a mistake in my calculations or something.... ;-)