Solar help for a noob

[Primal1]

I can easily put 300W maybe 400w on the roof of our Honda Element. I'm planning a small 100AH battery bank to run my CPAP and such at night.

We will be traveling to shows and making knives and kydex sheaths and holsters on the road. Can I plug an inverter into the controller and use it to run power tools off of the sun during the day or does it all have to run through the battery bank first? I figure we will only be working in the daylight so my heavy power needs will while the sun is available. 

I will be using a bench grinder and a toaster oven along with a heat gun for heating kydex, is this a possibility or should I just get less solar and plan on running those off of a generator?

I was planning a Renogy PSW 2000W inverter to provide for the 1500W heat gun draw.

Does the controller type PWM or MPPT make a difference for this application?

 

[tx2sturgis]

Lets recap:

CPAP all night.

Toaster oven. (not sure of duty cycle)

Heat gun. (same)

Bench grinder. (probably intermittent) 


That's just way too much power you are wanting to pull from one battery and 300 watts or so of solar on a small SUV.

You might be able to run the CPAP all night, but that system will probably need a half or full day of sun to recover. 

So the heat generating items and the power tool will most likely need a genset for power.

If you double that battery capacity and double your solar panels, you might have the ability to do some of that plus some surplus. Maybe.

 

[Primal1]

Ouch, thank you. Guess it's back to the drawing board. I can maybe add a little more battery bank and some off vehicle panels but weight and space in an Element are a premium as it is.

 

[Weight]

To operate your on-the-road-shop as you describe, you need a generator. To operate your CPAP keep the most solar you can fit on the top. Get at least two 6 volt golf cart batteries cabled as 12 volts.

 

[DLTooley]

CPAP draws are being way overstated here. Mine draws about 1 amp on average at a moderately high setting. That is without the humidifier, which most people do. Recall that the pressure drops substantially on your out breath and this also greatly reduces the power draw.

How often you use the heat gun and bench grinder is what is important. You will need to use the battery as those draws short term exceed the max output of your panels. It is best to wait until after your batteries are charged back up to float stage in the morning before doing the heavy draw. This requires **less** battery, but you will need to make sure you get recharged before dark. Not getting up to 100% occasionally is okay, on a daily basis definitely a battery killer.

It all depends on your frequency and duration of use. A generator is definitely something to consider. For CPAP, a 100 watt panel and a 100 ah battery is plenty - so long as you are not in a cloudy area. Wait until afternoon to charge up larger devices, like the Ryobi portable power tools (which have a 12v charger option) or a laptop.

 

[John61CT]

So many variables, you probably would need to go "too big" to cover worst-case scenario with solar-only.

If only for occasional short times, running the engine to get high alt output might be enough, put a KillaWatt on the tools to learn their actual draw.

But really carrying a small genny gives the most flexibility at lowest cost, can also help keep your bank charged when solar isn't enough.

 

[Primal1]

Thank you all for the input! I'll be ordering a kill a watt ASAP.

I'm researching propane ovens and battery powered heat guns to see if they will be a more cost effective solution to our work needs. I'm currently thinking 200 watts of solar and pair of GC batteries for the CPAP just to be safe and hopefully have a little power left for phone and laptop charging.

 

[willprowse]

need much larger battery. also, honda element roof would be filled to the rim if you stuck 400 watts on it, I think.

could just use a generator for the toaster/heatgun/grinder, and use solar for the cpap and laptop/lights etc

 

[John61CT]

Thank you all for the input! I'll be ordering a kill a watt ASAP.

I'm researching propane ovens and battery powered heat guns to see if they will be a more cost effective solution to our work needs. I'm currently thinking 200 watts of solar and pair of GC batteries for the CPAP just to be safe and hopefully have a little power left for phone and laptop charging.

Now you're on track!

But if you can't fit more solar that low ratio means you'll need to be careful, learn how to make sure you get the bank back to true 100% Full a few times per week to make it last.

In other words to use less than you put in.

And if really dependent on solar, you need to be ready for worst-case conditions, not base your setup on best or even usual ones.

The little genny gives a lot of flexibility in that regard. Or regular overnights on shore power.

Also a lot of driving can give the alt added value.

 

[Primal1]

So I got my kill a watt and I'm totally baffled. I ran the CPAP all night and got a reading of .03KWH for 7 1/2 hours of use.

Am I correct that converts to 2.5 mAH on a 12v setting? Pretty negligible by itself correct?

In case anyone is curious, I checked a few tools we will be using (with a generator for some)
Drill 121-150W
Dremel 40W-low setting 96W on highest speed.
Heat gun low setting 50-600W High setting 600-1300W

 

[MrAlvinDude]

So I got my kill a watt and I'm totally baffled.  I ran the CPAP all night and got a reading of .03KWH for 7 1/2 hours of use.

Am I correct that converts to 2.5 mAH on a 12v setting? Pretty negligible by itself correct?

hmmm....   I get: 

 .030kWh = 30Wh

30Wh / 7.5h = 4W per hour 

4W / 12V = 0.334A = 334mA per hour

So in 7.5 hours that would be 2.5Ah of battery energy. 


As this is measured at the 110V side of things, add some conversion loss to the inverter. About a 30% loss is not uncommon (giving you a 70% efficiency on the inverter). 

So 1.3 x 2.5Ah = 3.25Ah 

Somewhere around 3.25Ah of battery energy - to run your particular CPAP for one night.

 

[Primal1]

Cool, thank you, The numbers were so small I thought I was doing something wrong! I'll be ordering the 12v power cord for it as well just to avoid inverter loss.

 

[Knit]

I can run my 12v native Cpap for almost two nights on a 96 Wh battery, so your measurements are about right. Sounds like your Cpap is slightly more efficient than mine. I do find that my Cpap is fairly sensitive to voltage and really needs 12v or higher to run. The battery I use is really a universal external laptop battery, a BP96 from Bixpower. In my RV, I have 220Ah and running it takes only a fraction of what my refrigerator draws.


Sent from my iPad using Tapatalk Pro

 

[DLTooley]

Your numbers do seem a bit low, but not impossibly so. I run around 10 watts at what is probably a higher pressure setting than yours. To be safe double that number to give yourself some wiggle room.