DIY Solar/Trimetric/6 Volts on a 2015 Grandby

[DrJ]

I took delivery of a new 2015 Grandby Front Dinette Model about a month ago.
I was ready to setup the 12 volts system to my camper and here is how I planned it out.
Hopefully this helps some of you who are looking to do the same thing.

My last setup had a wonderful battery/solar/monitor setup and I wanted to make this one similar in performance.
Here were the last specs:
200 amp hours of 2x12 volt AGMS
340 Watts of Solar glued to the roof (never came off - see below)
1 trimetric 2030 monitor

New Setup
210 amp hours of 2x6 volt AGMs
250 Watts of Solar from rigid panel
1 trimetric 2030 monitor

When sizing a battery/solar/monitor setup you need to ask a few questions:
1- How much power am I going to use in an average day?
2- Do I have enough battery power to make it at least 1-2 days without any power coming in?
3- Is my solar enough to charge my batteries and run my system during the day time hours?

Question One
How much power an I going to use in an average day?
From my last FWC Hawk, I used an average of 40-60 amps per day with most of that power coming from my 110 litter 2 way fridge and my furnace. See this for more information:
http://www.wanderthewest.com/forum/topic/9301-measured-fwc-power-use/?hl=%2Bmeasured+%2Bpower

My new Grandby has the same fridge and furnace. It does have a few more LED lights but those are pretty minimal power users.

I use an average of 50 amps per day.

Question Two
Do I have enough battery power to make it at least 1-2 days without any power coming in?

I have calculated that I need about 50 amps per day (maybe less) of energy to run my system without an issues.

2 days = 100 amps

I can safely discharge about 50-60% of my battery bank without damaging it.

So I would need at least 200 amp hours of battery power.


Question Three
Is my solar enough to charge my batteries and run my system during the day time hours?

During the day time hours when it is warmer, my fridge cycles on more often. I use some lights and occasionally charge items during the day.
With those needs, I could be using up to 5-6 amps at a time during the day.
My solar would need to overcome that plus recharge my batteries.

In Idaho I would get 5 solar hours a day.
You can figure out your solar hours from here:
http://www.wholesalesolar.com/solar-information/sun-hours-us-map

50 amp hours to recover divided by 5 solar hours = 10 amps/solar hour

To recharge my system I would need to generate at least 10 amps per solar hour and 15 amps would be ideal.

amps x volts = Watts
10 amps x 14 volts of charge = 140 watts (adequate)
15 amps x 14 volts of charge = 200 watts (ideal)

There is some voltage loss from the controller, wiring, etc.. There is also some cloudy days, parking in the shade, etc... to overcome.

So I went with 250 watt panel.

But I do think 150-200 watts would have worked ok too as long as I was careful.

I originally had 270 watts of flexible panels, but my glue down job was subpar and the panels were not well constructed for this type of use. And they went flying off my camper during the first trip.

So now, I have a heavy, big, and rigid panel.
It works great.

Here are some pictures of my handy (sort of) work.

New 6 Volts vs older 12 volts

New Batteries fit perfect in front dinette setup

Trimetric Wiring Setup

Placing the Trimetric Wiring in

It's a really big panel

Last glue on panels worked great, until I started driving

 

[smlobx]

Great write up!

One question. Do you have your truck wired up to charge your batteries when you're driving? Or is it that you spend several days in one spot?

 

[DrJ]

Great write up!

One question. Do you have your truck wired up to charge your batteries when you're driving? Or is it that you spend several days in one spot?

We will often stay in one location for several days at a time. The truck does charge the camper. In my prior setup, I was able to get around 15 amps/hour of charging while driving. I believe that will be about the same this time, but I have not directly measured it yet.

 

[photohc]

Nice job DrJ! Also, a very realistic analysis of the system sizing. I am curious on what kind of panel is that new one? 12v or 24v and what is your charge controller?

 

[DrJ]

Nice job DrJ! Also, a very realistic analysis of the system sizing. I am curious on what kind of panel is that new one? 12v or 24v and what is your charge controller?

New panel is Renogy 24 volt 250 watt panel.
I have a 20 amp MPPT charge controller - which was necessary for a 24 volt panel.

I chose the panel because I could get it from amazon and it was wider than my yakima tracks.
So it made it very easy to attach the panel to the tracks and not drill into the roof.

 

[billharr]

Nice panel. I am going to add another 100w to the top of my Hawk. If I knew what I know now I would have gone the 250w panel and mppt controller. I like how it spans the tracks, I have to use alum angle to reach the tracks.

 

[97grandby]

Wow drj, nice set up. When over kill is under rated, I think I'll check with you before I add a system on my truck. Are you planning on adding any kind of inverter so you could run 110? About the only thing your missing from your system is a tv.


Sent from my iPhone using Wander The West

 

[DrJ]

Wow drj, nice set up. When over kill is under rated, I think I'll check with you before I add a system on my truck. Are you planning on adding any kind of inverter so you could run 110? About the only thing your missing from your system is a tv.


Sent from my iPhone using Wander The West

I have been thinking about that - or even a small microwave like you want to do.

A TV would be great (or at least my kids would think so) but I'd probably just do a 12 volt unit if I didn't do the inverter.

 

[97grandby]

I have been thinking about that - or even a small microwave like you want to do.

A TV would be great (or at least my kids would think so) but I'd probably just do a 12 volt unit if I didn't do the inverter.

I'm thinking where to mount a tv in my grandby. If I could some how mount to my rear lift panel would be the ideal space. Any one else mount a tv in their campers?


1990 Ford F-250
1997 fwc grandby

 

[Wallowa]

Dr,

Great evaluation and appreciated. Estimating solar hours seems difficult considering the orientation of the panel on the roof; let alone the sky cover differences. Your empirical data makes sense.

We will order a Hawk on 11/18 with the 160W fixed and 80W portable panels. Here at home 45.407N/117.261W with an array of 22 280W panels [@230 degrees] we see enormous differences in KWH production. I hope and trust the Hawk system will keep us up and running for at least 3 days in one location [with OEM double battery set up/furnace/110L 2 way]. Time will tell. Your average power use was very helpful.

Thanks!

Phil

 

[rotti]

I hope and trust the Hawk system will keep us up and running for at least 3 days in one location [with OEM double battery set up/furnace/110L 2 way]. Time will tell.

I have a 12 Hawk with the same frig and factory dual batteries. I only have a single Renogy 100w portable suitcase solar panel and on a recent nine day hunting trip I had plenty of power. I had a couple of cloudy snowy days and cool/cold temps in the mountains of Colorado. I used the furnace hardly at all (a big draw.....I use a good down bag) and I did "re aim" the panel three or four times a day. You should be fine.

 

[DrJ]

Phil,

I actually think the 160 watt zamp solar system that FWC uses now is a pretty decent setup. For the majority of people with compressor fridges and furnaces, this would be adequate. If you get less solar hours or use more power it might be a stretch, but many owners don't.

It is a big improvement from the 100 watt panel. I would assume that panel is not quite enough.

 

[pawleyk]

DrJ,

Where did you install your solar charge controller? Is it connected to the coiled 10ga in your battery box?

 

[DrJ]

It is mounted on the "roof" of the battery compartment. It is a 20 amp MPPT controller and seemed to just barely fit in there. I can't see the indicator lights but it works great in that spot.

 

[pawleyk]

Perfect. So the solar lines in the box are just direct leads from the plugs on the roof and rear wall?

 

[pawleyk]

Also, I seriously owe you a beer or two.

Thanks for all the help!

 

[DrJ]

Perfect. So the solar lines in the box are just direct leads from the plugs on the roof and rear wall?

The solar lines are direct from the solar. You can hook them up directly to the solar controller.

In this picture you can see the solar controller above the batteries.

 

[carld]

Have you considered that you can only charge the batteries to 100%. So if you go two days with little or no solar your starting point is at say 50% charge. If the charge current is just a little more then you use, you may only be at 60% at the end of a full solar day. It may take more than one full sunny day to get the batteries to 100%. A 200 Ahr battery at 40 to 50% charge requires more than 100 Ahr (150 Ahr including camper load current) per day to fully charge them. Not only that but because of the non-linear characteristic of the batteries you may have to apply a high voltage low current over 4 to 6 hrs to raise the battery charge from 80% to 100%. I don't know just something to consider.

 

[DrJ]

I purposely sized my solar system to do just that. It could make up 100 amp hours in one day under ideal conditions.

250 watts/14 volts = 17.85 amps X 6 solar hours = 100+ amps

Collecting solar is rarely "ideal" where I camp so I also have a 135 watt portable panel that can be run at the same time.

It's quite easy to get to 100% of a 200 amp hour battery with 385 watts of solar working for you.

 

[carld]

It could be a little more complicated than that. The battery can only absorb so much charge depending on its charge state. Suppose you drive to a site starting in the evening and the battery is at 100% from the car alternator. The battery discharges all evening and night and by sunrise it at 75%. By noon the battery reaches 80%. At this time the battery will limit the charge current and I think it can drop to maybe 200 mA or less. For the remainder of the day ( 3 or 4 hrs) the battery will charge to maybe 90% depending on the type of charge controller. The charge controller should bump the charge voltage up to 14.2 V during this time otherwise the battery will stay at around 80%. Then you have another evening and night starting 80% this time and the next day at noon your at 70% charge ... then 60% on day 3 and 50% on day 4. And this assumes that each day is a nice sunny day. Note that adding more solar charge power does not really solve the problem since the battery limits the current based on its charge state so the extra available charge current cannot be used. The MPPT changes the operating point on the PV voltage current curve to operate closer to the PV open circuit voltage at a low current. Also the MPPT should try to increase the battery voltage to 14.2V to push the charge above 80%. Increasing the battery size helps.