Bambi Prepping for Solar and Boondocking

[Spudnickle]

In preparing for future boon docking in the near future on a 50% full time, I'm adding solar. I have switched all lights out to LED's, removed the micro wave and I'm somewhat conservative with energy use.

Because of this, I choose to go with 2-100 watt panels with a 30A PWM - Max PV input volt 50 VDC controller. This is ordered so I will use what I've ordered. Just need to know about using existing wire since new wire with my kit is the same gauge. I will being installing myself before leaving for a 3 week trip south of the boarder.

Here's my question;
Any reason I can't use the AWG 10 wire that is pre install in my 2014 16' Bambi? New wire with the kit is also 10 gauge.
I'm not worried about loosing a little watt transfer, if I don't have to run the new wire. I now know where the pre installed wires are and it would save me lots of time and grief if I can just tie in.

More info; I only have 2-12 v batteries that I want to stay topped off. If I find in the future I need more juice, I'll add a portable 100w suitcase.

I also went with 2 panels after deciding to remove my TV antenna since we don't use it. May watch a DVD once in a while. Figured next owner or me could add a more compact antenna down the road if desired. I installed an inverter a few months back, so I'm good there.

I know there are many opinions out there, but just would like to hear a bit of new feedback on the question knowing the above info and I'm also good with only 200 watts.

[robinjen]

10 AWG pre-wire should be fine, will handle a good amount of amps. I'm running one group 27 battery and 100w of solar. Good for most of the time but gets pushed on very cold nights when the furnace runs a lot. I'm planning on adding another 80-100 watts on portable panel for next year and perhaps switching to twin 6v batteries for more capacity.

[SilverHouseDreams]

Your biggest energy hog is the inverter, your best bet is to evaluate what you would ever power with the inverter and replace that item with an actual 12V version (e.g. the TV). We have a small "portable" inverter that plugs into the 12V receptacle that we could use if we ever needed it (perhaps to use TV to watch emergency news updates or something?), but in general if you want to operate on 12V you need to forget using an inverter as it is just horribly inefficient. If you were in a coach with 400Ah of battery that would be different, perhaps...but then you'd also have a generator to always replenish them.

If you need to power a laptop computer, buy a car charger for it. Thankfully that is even easier with the new USB-C powered laptops as there are plenty of 3rd party USB-C power ports that plug into 'cigarette lighter' jacks. To charge your mobile devices, use a car charger and not a 120V charger.

[Spudnickle]

I suppose I'll need to do more research on the inverter. Didn't realize it was a hog. I put it in to perhaps watch a DVD once in a while but in 8 months, have only watched one. Other than that, I thought I'd charge the cell phones daily. My inverter does have a on off switch. I also have two "cigarette lighter" ports plus the controller I'm getting has a USB port.

Looks like the solar kit will be here before the weekend so I'll be able to get it hooked up and some testing done before we hit the road in a month.

Thanks for the feed back.

[alano]

If you're planning on boondocking lots then you might consider adding a battery monitor. These devices tell you at a glance how much battery capacity you've used and the measurement isn't affected by whatever load happens to be on the battery. They use a shunt resistor to constantly monitor the current into and out of the battery.

[SilverHouseDreams]

Originally Posted by alano

If you're planning on boondocking lots then you might consider adding a battery monitor. These devices tell you at a glance how much battery capacity you've used and the measurement isn't affected by whatever load happens to be on the battery. They use a shunt resistor to constantly monitor the current into and out of the battery.

I second and third this. It is the only real way of knowing what is going on. The new Victron BMS-712 Smart with built-in Bluetooth is pretty fantastic, I tried a cheap $18 thing on Amazon but it wasn’t remotely accurate.

A true battery monitor will show you the load going out, time left until “empty”, and the charge rate going back in...AND accumulative amp hours going in/out. This will allow you to actually plan for longer outings.

[pteck]

I just got done installing 200W of solar on my 27FB. You'll want it in parallel, though that's the only option with PWM anyways. It'll perform great.

You're on the right path. 200W can absolutely be supported by the stock 10gauge wire.

Losses are minimal. It's never talked about but the majority of the charging takes place at far lower currents than the rated max output. Also, the panel run at higher than 12V (~16-18V). There's actually very little time in the day at peak output, and then your panels would have to be perfectly aligned and tilted which is almost never the case with RV installed panels.

If you want a battery SOC monitor, the simplest is just to add a cig light USB charger, with voltage readout for ~$10 on Amazon. Basic and effective. While it's great to geek out and see the actual load/amp readouts, it's not completely necessary.

[alano]

I'll agree to disagree with ptech, although all of his previous posts have been spot on!

Battery voltage is a poor indication of battery capacity as it's affected by temperature and load conditions. Even when unloading lead acid batteries the recovery time is relatively long - some folks recommend 4 hours!

In addition to displaying the percent battery capacity that you have available, a true battery monitor will tell you the net current flowing through the battery so you can easily estimate how long you can continue to deplete your system before you reach your target.

Although using battery voltage can be used to measure capacity, a real battery monitor is a more accurate method.

[pteck]

I don't disagree. More data is always good and certainly offers a clearer picture of what's going on. But I'm an engineer and it's easy to want to geek out on things. But sometimes, more is just more.

You have to ask yourself if there's value in the added cost and complexity, for yourself, as only you can answer the value proposition.

Even without solar, a battery monitor would be useful no? But heck, the majority of us have gotten along with the dumbed down MicroPulse green/yellow/red monitor for how long now?

A $10 voltage cigarette lighter offers much more useful information if one can interpret it, at very minimal effort and cost. Which sounds like a good fit for the OP, which was my point.

[SilverHouseDreams]

If we want to keep “simple”, then perhaps the solar controller has a voltage readout on it...but, anytime the sun is up you won’t be able to truly assess SOC by voltage, just as you can’t if any real load is present.

[Spudnickle]

In addition to displaying the percent battery capacity that you have available, a true battery monitor will tell you the net current flowing through the battery so you can easily estimate how long you can continue to deplete your system before you reach your target.

Thanks for the input. I have thought about buying a monitor but the new Victron is more than I want to spent at the moment.

However, I'm with pteck on the Micro Pulse Christmas tree light monitor. I never have liked it. I would like to have more detail when it comes to monitoring my batteries. I want more detail.

The solar controller I'm getting is suppose to tell me how much load is coming in, but not what's leaving the batteries.

I may go ahead and get one of the voltage cigarette lighters for this coming 3 week trip to Mexico and see if it is enough for me to track my new system.

Thanks for all the tips as I am on a major learning curve.

[AnnArborBob]

The following comments come from someone who spent approximately six of the last ten months without electrical hookups while boondocking or staying in some national, state and local campgrounds that did not have power. Our 27 foot Airstream has 740 watts of solar panels on the roof to keep our 600 AH LFP batteries topped off. We also do not have a propane fridge, but rather a 12 volt fridge using a Danfoss compressor. This setup allows us to live as if we did have electrical hookups even when we don't. I mention these facts only so you can know that I have some genuine "real world" experience with this subject.

The inverter itself is not really an "energy hog" as it only uses two to three amps per hour when idling (of course, if you leave it on 24/7 it can become the aforementioned hog.) It's what you run off the inverter that can be the energy hog. Look for a 12 volt television (they make them and can be found on Amazon.) Many 110 V AC televisions really run on a much lower voltage and have a transformer to step the voltage down from 110 to whatever the TV needs (e.g. 12v, 18v or 24v.) I've never looked for a 12 volt DVD player but they may exist.

Your real energy hog as you boondock in the winter will be your furnace fan. It uses about 9 amps per hour. So if it runs 50% of the time during a typical chilly 12 hour nighttime in the winter, which is typical for us in January in the Arizona desert, you're looking at 50 to 60 amps of usage overnight. I'm not sure of the stock battery capacity of the Bambi, but I'd be surprised if it was more than 180 AH of which only 90 AH are usable without damaging the batteries. That means that on a cold winter night you will use up 1/2 to 2/3 of your battery capacity just to run the furnace.

In the dead of winter when the sun is low in the sky our 740 watts of solar panels (tilted towards the sun) can provide around 250 to 300 amps of electricity to our rig which is usually sufficient to bring our batteries back up to 100% charge and run the fridge (which uses about 90 amps in a typical 24 hour duty cycle.)

If I prorate to your 200 watts based on our actual experience with 740 watts of solar during the winter, I would expect your solar panels to provide you with around 70 to 80 amps per day which might be enough to replenish your batteries (in your case, it all really depends on your furnace usage but you mentioned you were going south of the border so I am assuming you mean Mexico where the use of the furnace might not be as significant as it is for us in Arizona and SoCal.)

So in answer to your original question, with 200 amps of solar panels and 180 amps of batteries (my guess of your capacity) you might be OK, especially if you don't need to run the furnace a lot overnight. But, if you do need to run the furnace a lot, know that you don't have a lot of excess capacity so be prepared to add 150-200 watts of portable solar panels to your arsenal. I'm not sure how you would hook up the portable panels so they would work in tandem with the panels on the roof and their controller. But I am sure that the answer to this question is readily obtainable.

Best of luck and have fun!

[Spudnickle]

Thanks Bob,
I've rafted most of my life so using lots of battery power has not been my style. So the little 16 foot Bambi is like a castle to my wife and myself. ( spent 3 weeks rafting the Grand Cannon last year.) So we really don't need a lot. This is a joy to have and looking forward to see more of the country. One good thing is my furnace will run off of propane. I know my new controller will run 200 more watts if I decide to add the portables. Thanks for your input.
Greg

[AnnArborBob]

You're welcome Greg. Enjoy the adventure!

One other thought. Roughing it for a weekend or even a week or two is fine. But once you are on the road for an extended period of time, you will want some more "comforts of home." Just know that this is a normal part of your Airstream development and not a personal failing!