PWM loves poly

[this is an old draft I’m going to publish]

I was thinking about how common 100W Renogy panels are (both mono and poly) and how to extract maximum power from them with PWM controllers.

The question is on my mind because no folks will link to one of Renogy’s mono/pwm kits and ask for feedback.  I am annoyed that they offer mono/pwm at all;  it’s an inefficient Continue reading “PWM loves poly”

Backchannel: Alpicool C15 + Jackery 500

from an Amazon product question for the community:

How does anyone feel about using [the Alpicool C15 compressor fridge] with a Jackery 500? I’d love to hear from the more battery-math folks! Any thoughts are appreciated!

I’m not really a battery-math person, but I’ll take a first swing at it and other folks can chime in with corrections.

The Alpi is great, no caveats there. My feelings are that $500 for the Jack is an expensive way to get 40Ah of usable battery capacity. Such devices are set up for convenience on short outings. Not a fit for me, but maybe it is for you.

As far as the math, the capacity of the Jackery is “518Wh/144,400mAh”. Let’s decode that spec: 518Wh is an accurate measure of capacity, equating to about 40Ah @ 12v. Normally I’d say the use of Wh instead of Ah is puffery, but in this case there is a good reason for it (beyond the scope of this comment). Since the little Alpicool pulls about 12A/day, we can assume the Jack will power the fridge for about three days between charges if you run it off the DC outlet. Running the fridge off the the 100v inverter in the Jack would impose inverter-related losses of about 10%, cutting it close on the three days.

The “144,400mAh” spec given up top is deliberately misleading. First off, that’s a fluffy way to write 144.4Ah. Second off, you can’t get 144.4Ah out of the device since that figure was achieved by multiplying the capacity of each individual lithium cell by 3.6v. You cannot access the individual cells so the figure is meaningless for practical purposes. The real information can be found if you look up the unit on the Jackery website and click on the Specs tab: “144,400 mAh / 3.6V

I’m *not* saying the Jack is a bad unit. I’m sure it works as described and I like the higher internal voltage. The ideal customer would be charging on friday and camping over the weekend. Easy peasy. For longer outings, the long charging times (8hrs on wall socket, 12hrs *driving* or solar) would put a stick in your spokes. What happens to the food in the fridge if you have to take the Jack into Starbucks to charge?

What kind of vehicle is this going in? If van, SUV, Subaru or other adventure chariot 🙂 and you camp often (or fulltime) , consider what you could get for that same $500 if you are careful:

This solution would yield power automatically and practically forever. No hunting for power outlets. Zombies could take over the grid and you’d have cold beer in the fridge in the middle of Idaho. Or you could store insulin or zombie vaccine. Or more beer.

backchannel: solar harvest, battery charging

from this post:

Although solar is sold to the public as watt/hr rated panels, to achieve their sales rating the panels must be oriented perfectly facing the sun, on a cloudless day, with no obscurations or diffusing humidity to achieve their rated power.

I’d say it’s an apples-apples objective rating which salescritters might [mis]use to make a sale. For onlookers, lab ratings are done at 1000W of light per square meter with cell temps of 25C (ambient approx 0C.)

Cell temp is specified because panel maximum output decreases as cell temperature increases. Luckily it can be calculated easily. Note to new folks: losses due to heat are the reason we leave airspace under panels. That way air can get under the panels and wick away heat from the bottom of the cells, which is typically 50-60F higher than ambient.

Example: today’s 100F temp in El Paso means my panels will lose 21.24% Continue reading “backchannel: solar harvest, battery charging”

MPPT vs PWM in cold weather

This post is inspired by a comment from Jeremy.

I plotted MPPT+mono panels, MPPT+poly panels, PWM+mono, and PWM+poly against ambient temperature to see how the combinations fare.

The guinea pigs were the Renogy 100w mono (Vmp 18.9v, Imp 5.29A) and 100w poly (Vmp 17.8v, Imp 5.62A) panels.

We assume full overhead sun, Vabs 14.8v, and 50% Depth of Discharge 12.1v.  Note that the graph starts at 50w so we can see some detail.


Continue reading “MPPT vs PWM in cold weather”

How MPPT works – video

Here is a MT50 display connected to a 4215BN mppt controller.  The controller is holding Float voltage (Vfloat).  Note that the screen we see here is stats on power coming from the panels into the controller.  No down-conversion or charging/load amps are shown here.

So little power is required to hold Vfloat that the controller has driven panel voltage (Vpanel) up to nearly Voc.  In the summer heat Voc of these mono panels is a little under 40v.

I apply the load (dust devil — turn down your audio!) and the controller drives Vpanel  down toward Vmp (around 36v), thus increasing panel output.

I remove the load and Vpanel rises back toward Voc and output drops.

Continue reading “How MPPT works – video”

backchannel: craptastic Chinese cheap stuff

from this post:

Since a dongle can be used to program multiple [victron 75/15 charge controllers], it becomes more and more practical togo with such an excellent SC rather than the craptastic Chinese cheap stuff.

Ok, let’s compare the Indian (Victron) cheap stuff with the Chinese (Tracer) cheap stuff.

I looked for the cheapest prices for each on eBay and Amazon.

Victron 75/15 Tracer 2210A difference
charge controller 88 98
display or dongle 50
temp sensor 24 6.5
total 162 104.5 35.49%
input voltage 75 100 -33.33%
current 15 20 -33.33%

Do you want to pay 35% more for the Indian controller with 33% lower max input voltage and current rating than the Chinese controller?  Totally up to you.

If I wanted to use Victron on my own system it would have cost $570 for the 150/45 vs $231.50 for the Tracer 4215BN.






backchannel: cheap controllers == batterycide?

Responding to this post.  Taking it backchannel as the OP specifically asked us not to derail.

I just bought one of those cheapie $20 newer pwm controllers ( the kind you are seeing now with the 2 usb ports) for a 100 watt panel I installed. It sux.  When my rig is plugged into 120v power, the cheapie pwm solar controller won’t go into float ever, so it raises the voltage to 14.4 and sits there all day,

My curiosity was piqued earlier when you said yours had stages;  mine doesn’t and none of the others have seen like it do.   They are often advertised as multistage pwm but are actually just on-off controllers (sometimes called shunt solar charge controllers).
Continue reading “backchannel: cheap controllers == batterycide?”

“Unless you have a large solar array…”

Here’s the post I am restraining myself from addressing on the forum

Unless you have a large solar array, MPPT are not much better. If you have high voltage panels, the MPPT can produce a bit more power. That is why folks use series connections as that doubles the voltage. You are better served with a quality PWM than with a cheap MPPT. I have 400 watts on the roof with a 45 amp PWM by Morningstar. The panels are parallel. If one has shadow, the others do not suffer.

So much wrong in just one paragraph.

[And so much wrong in my response!  See updates below]

Continue reading ““Unless you have a large solar array…””