Checking my assumptions

[Suanne]

Using my current computing devices with a Kill-A-Watt meter, I measured my power usage. My devices include an HP3105m notebook, Samsung Galaxy S II smartphone, and a Verizon Jet Pack hotspot. I measured watts based upon normal usage, as well as with more/less loads. I measured with my devices connected to regular house current (110v). I've order an AC/DC converter to measure usage when connected to 12v once it arrives.

Assumption: Using 12v connections (no inverter), usage should be lower with 12v than 110v. Correct?

I've calculated the usage on my computing devices to be almost 360 watts per day. This is a high estimate, but doesn't include the occasional usage of other items (fan, battery charger, etc.). 360 watts calculates to 30Ah on a 12v system, correct?

Assuming I need at least 30Ah per day, then a 12v 75Ah deep cell battery should be sufficient, correct?

Assumption: A 100w solar panel (suitcase) is sufficient to keep a 75Ah battery healthy in the summer sun of the desert SW, correct?

Assumption: For the cloudy days, I can hook up the house battery to my starter battery with jumper cables (while engine on) to do a fast charge, up to 80% SOC, correct?

Assumption: Given the same usage time, keeping my notebook/laptop plugged in and charged uses less electricity than recharging them, correct? Is this also true for a smart phone and hotspot?

I'm sure I have other assumptions, but that's enough for now. Thanks in advance for your help.

Suanne

 

[PastTense]

I think the measure should be 360 watt hours, not 360 watts.

I really question your fundamental assumptions:
1. That you are only going to be using electricity for a few electronics. That you won't need it for lights, fans, small kitchen appliances, refrigeration, electric drill...
2. That it is always going to be sunny daylight--never cloudy days...

 

[Suanne]

Thanks much for your reply Past Tense. You are making me think.

If I go the route outlined in my assumptions, I'll be in my '04 Prius. I should have stated that in my assumptions. I've lived out of the Prius, off and on, for the past 5 years with 6 months being the longest continuous period of time. So, based on that experience, I'm pretty confident that my electronic devices make up almost all of my electricity needs.

Since I'll be staying put for months at a time this winter, I thought I'd try solar vs. my past practice of re-charging my devices by turning my car on (hybrid's engine/ice only runs intermittently).

Will recharging the house battery with jumper cables from the starter battery be a sufficient method to off-set low solar production days? Is that an OK way to keep my house battery healthy?

Suanne

 

[akrvbob]

Yes, if you are in the Prius, your assumptions are all good. After all, it's just a giant generator on wheels! The solar panel is just icing on the cake!! Most days you wouldn't need the Prius at all but it will be there if you do.

However, the difference in cost and size between a group 27 and either a group 29 or 31 is so little I would get one of those instead. I'd get the group 31 for sure.

Does this mean you have decided to come in the Prius instead of the RV?

You are a remarkable person Suanne! :heart:
Bob

 

[TucsonAZ]

Suanne, everything seems fine to me, I don't know how charging from a running vehicle via jumpers will go but you will adjust accordingly I assume. I'm sure the Prius will do a better job with that task than a normal car would.

If it were me, I would adjust two things. Firstly, I would try to fit a little more solar on via a roof rack, mount maybe a 200w panel up there which will be sure to top off your battery in all but the worst of conditions.

As was mentioned, I would attempt to go with a slightly larger battery if you have the room, I'm not sure where you're putting it though and if you need AGM or if they will be outside.

Those two things will ensure you have the power you need and won't cost you that much more.

Since you're in a Prius however, I'm going to guess there's a better way, check out this thread.

http://forum.solar-electric.com//showthread.php?12962-Using-a-Prius-as-a-generator

 

[Suanne]

Thanks Bob and TAZ. And TAZ, thanks for the link for using a Prius as a generator. I will definitely check it out.

... the difference in cost and size between a group 27 and either a group 29 or 31 is so little I would get one of those instead. I'd get the group 31 for sure.

I'm still not clear about the group numbers. Are those dual-purpose marine batteries? I was looking at a 12v AGM deep cycle wheelchair battery. It seems that it should be made to cycle lots of times (like golf cart batteries). I'm still learning here and looking for advice. I want to get the largest Ah battery that a 100w suitcase solar panel system will support and keep healthy during the desert SW winters.

Does this mean you have decided to come in the Prius instead of the RV?

I keep going back and forth between the RV and Prius for snowbirding this winter. The RV has 232Ah batteries which would be more than enough for my electronics and then some. But, the panels and controller to feed them is more expensive than what I'd like to spend. Plus, to be honest with myself, I'm afraid I'd be very tempted to spend more time inside the RV than I really want to; just because it's comfy and I'm an introvert. That's how I am at my sticks-and-bricks.

If I snowbird out of the Prius, I know it's comfortable enough to lounge inside if the weather dictates. But, it's not so comfortable as to entice me to stay inside when the weather is good and I can be among friends.

Plus I'm concerned that the RV's poor gas mileage would be like an anchor that would keep me from wandering. With the Prius, I'd not only save money driving to the southwest, but I'd also feel freer to explore the area if/when I wanted to.

Either way, with the Prius or RV, if I like snowbirding I'm going to start looking for a van in the spring.

Suanne ... whose wishy-washy, but leaning toward the Prius for this winter ...

 

[wagoneer]

Good for you!! my brother (the rich guy in the family) bought a Tesla and a bunch of Tesla stock (laughing all the way to the bank) I would love to take that to the RTR could power a small hoedown. A van will serve you well if big enough could tow the Prius. Go for a Ford 2000-2003 7.3 diesel.

 

[akrvbob]

Suanne, generally, anything listed as a "group" is a marine but there are exceptions. You would be better off buying a true deep cycle but it's hard to be sure it's a true deep cycle and not a marine.

If you can I'd suggest waiting to buy the battery till you get to Quartzsite and get the battery from Discount Solar. There price on batteries is about as good as anybodies and you will be sure it is a true deep cycle.

Plus, if you need future warranty work on the battery they will be the ones you brought it from and it should go smoothly.

I can sympathize with your dilemma! Being basically anti-social myself it's pretty easy for me to hide out in the trailer. But the only times there will be LOTS of people is during the 2 weeks of the RTR. Before and after there will be a dozen or less in camp. It isn't all that social, we have to kindof schedule group time. Of course people make friends and hang together but not the group as a whole. If you can make yourself be social for the 2 weeks of the RTR the rest of the time you might prefer the comfort of the RV. I find those times to be just the right balance of social time.

But then maybe you will get bored with just setting but not be able to travel because of the RVs terrible MPG.

It's a hard choice.
Bob

 

[Zil]

I think the charging system for the starter battery is no different than on a regular engine. The operating battery bank is unrelated to starting the engine, and is at a much higher voltage than 12.
Lead Acid battery must be taken to 100% at least weekly if not more.
Figure in some loss do to inefficiency, as much as 25% if multiple changes.