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Old 08-06-2019, 11:56 AM   #1
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Did I Do This Right?

Hey there, I just got little solar "generator" and ran a test to confirm the watt hours. But I'm totally confused by the result. Can you guys tell me, did I do this right?

I just wanted to do a super basic test, so I plugged in 2 lamps with incandescent bulbs totaling 100 watts (a 60-watt bulb in one, a 40 watt in the other). The generator is rated for 288 watt hours, so I figured it should power the bulbs for 2.88 hours... right? 288 / 100? That's 2 hours and 53 minutes, not taking any conversion/inversion losses into account.

The reason I'm so confused is that the generator exceeded that significantly. I was expecting less output, but I ran the test twice and both times got considerably more. So much more that I at first thought I'd forgotten to disconnect the solar panels, but no, this box was not getting any input, and was only putting OUT power. It ran the lights for well over 3 hours and I stopped with 3.5% still available.

So... did I miscalculate? Or is this thing simply a BEAST?
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Old 08-06-2019, 12:44 PM   #2
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I just wanted to do a super basic test, so I plugged in 2 lamps with incandescent bulbs totaling 100 watts (a 60-watt bulb in one, a 40 watt in the other). The generator is rated for 288 watt hours, so I figured it should power the bulbs for 2.88 hours... right? 288 / 100? That's 2 hours and 53 minutes, not taking any conversion/inversion losses into account. It ran the lights for well over 3 hours and I stopped with 3.5% still available.

So... did I miscalculate? Or is this thing simply a BEAST?
Rated watt-hours may be based on a maximum load that you weren't anywhere near approaching. So, yes, I believe that could be a factor. Resistance can make a difference here as well. Orrrrrr..... you could have gotten a much higher-capacity setup that was packaged in the wrong box...

Keep in mind, I am not an electrician by trade, I just remember a few things from my father, who was. ;)
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Old 08-06-2019, 12:50 PM   #3
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A 60W bulb only uses .06KWH
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Old 08-06-2019, 01:10 PM   #4
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Rated watt-hours may be based on a maximum load that you weren't anywhere near approaching. So, yes, I believe that could be a factor. Resistance can make a difference here as well. Orrrrrr..... you could have gotten a much higher-capacity setup that was packaged in the wrong box...

Keep in mind, I am not an electrician by trade, I just remember a few things from my father, who was. ;)
Ah, OK, if it's based on maximum load that could explain it.

I just bought a second one that looks identical but has a significantly higher watt hour rating, and it almost seems to line up with what I found, so I wonder if perhaps you're "wrong box" theory is correct... These devices are theoretically from two different manufacturers but their appearance is the same, so I'm thinking they were made in the same factory, and this first one is mislabeled.
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Old 08-06-2019, 01:12 PM   #5
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A 60W bulb only uses .06KWH
Right... I'm talking WH not KWH.
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Old 08-06-2019, 01:28 PM   #6
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Pretty much what Cheese_Wagon said.

A battery's actual amp-hour performance depends on the load you're powering. Less current per time, the greater the amp-hours available. Or, in other words, the faster you discharge a battery, the less you're going to get out of it in terms of total energy output. So the discharge rate they based their amp-hour rating on is most likely significantly higher than that presented by your test load-o'-lights.

I doubt (though don't know for sure) that their advertised rating is the maximum 'safe' discharge rate for the battery - unless their marketing department was asleep at the wheel - so you'd likely see the reverse behavior (lower AH performance than advertised) pulling a heavy load.

Now that you've satisfied your curiosity, I'd suggest you don't continue to see how long you can run something before the battery gives up the ghost. Each time you do you're shortening your battery's lifespan and reducing its total capacity.
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Old 08-06-2019, 02:09 PM   #7
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Well the bare minimum to do a CC load discharge test is a DMM and an ammeter, usually combined.

Ah counters are more convenient, but less accurate.

Actual load testers that automatically keep Amps constant as voltage drops are about $50-60 through the usual Ali channels, maybe Amazon marketplace and eBay.

They can be paralleled if you need to pull a higher load.

0.05C aka 20-hour rate is standard for lead batteries in the US, but for the various lithium chemistries, Peukert coefficient is close enough to 1.0 that a 3-5 hour test would be fine.

I spelled out more details here: https://www.expeditionportal.com/for...?posts/2633829
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Old 08-06-2019, 03:14 PM   #8
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Well the bare minimum to do a CC load discharge test is a DMM and an ammeter, usually combined.

Ah counters are more convenient, but less accurate.

Actual load testers that automatically keep Amps constant as voltage drops are about $50-60 through the usual Ali channels, maybe Amazon marketplace and eBay.

They can be paralleled if you need to pull a higher load.

0.05C aka 20-hour rate is standard for lead batteries in the US, but for the various lithium chemistries, Peukert coefficient is close enough to 1.0 that a 3-5 hour test would be fine.

I spelled out more details here: https://www.expeditionportal.com/for...?posts/2633829
Thanks so much for the info, but I really wasn't trying to get that fancy. I don't actually understand much of what you just said.

I am taking baby steps in my solar understanding, and for that reason have been focusing on watt hours, which seems like such simple concept. But now I'm completely confused again:

Quote:
Originally Posted by TheHubbardBus View Post

A battery's actual amp-hour performance depends on the load you're powering. Less current per time, the greater the amp-hours available. Or, in other words, the faster you discharge a battery, the less you're going to get out of it in terms of total energy output. So the discharge rate they based their amp-hour rating on is most likely significantly higher than that presented by your test load-o'-lights.

I doubt (though don't know for sure) that their advertised rating is the maximum 'safe' discharge rate for the battery - unless their marketing department was asleep at the wheel - so you'd likely see the reverse behavior (lower AH performance than advertised) pulling a heavy load.
OK, I was aware that amp hours would vary but I thought watt hours was kind of like a dollar: whether it's comprised of 10 dimes, 4 quarters, or one paper bill, it's still a dollar. I thought the whole point of watt hours was that, as a unit of measurement, it allows you to compare batteries of different voltages and to calculate your power needs across a wide range of devices.

I did not, in fact, find worse performance with a larger load, or better performance with a smaller load. Part of why I decided to test with lightbulbs (I don't have any kind of meter) was that I was surprised at what was happening when I ran a larger load, and I thought my math might be suspect, which is why I figured 100 watts would make it super easy to spot a bald spot in the logic. It's very discouraging to discover that the tiny little corner I thought I understood, I don't understand at all.

I've come across things in my research on this which would explain why the rated watt hours would not be accurate, but it seemed like it would be consistently inaccurate, not load dependent, and that performance would be worse, not better, than stated. I give up. Well, not really, but the more people explain to me, the more abbreviations and terms come out, the more confused I get. I thought it would be better to just get started than to wait until I know what Peukert coefficient is. Now, I don't know.
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Old 08-06-2019, 03:33 PM   #9
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Amp hours are a much better measure of battery capacity. Watt hours are needed when converting from one voltage to another.

The intentional obscurity and outright scamming of this market segment,

and let's not sanction their fraudulent use of "generator" - portable powerpak is better,

makes it difficult to determine just how bad their value truly is.

With lead, a high Peukert value means a bank hold many more Ah if discharging at a lower C-rate.

A 12V 100Ah bank discharged at 5A exactly, from 100% SoC down to 10.5V is the 20-hour rate, as I said is the industry standard.

Discharging at 20A rate 0.2C will give a completely different capacity number. That's Peukert in a nutshell.

Your mistake with the bulbs is assuming the nominal watts rating is the actual power consumed. Not the case, need to measure with an ammeter, and be able to vary the consumption in order to keep the amps rate as constant as possible.
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Old 08-06-2019, 06:12 PM   #10
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I disagree with the statement above.
The easiest way to estimate use is to calculate everything in watt hours and amps. Here's the best formula I use. 100ah at 100amps at 12v is 100amps x 12v 1200watt hours. It will produce 100amps for 20 hours according to spec, but who's using 100amps. You're using 100 watt appliance for 10 hours or 1000 watt hours.

Your 60w bulb may be 60w equivalent too. Most don't draw anywhere near the power stated. Try using a battery monitor. Pop this bad boy over the the chord and then you can see what's really happening.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 08-06-2019, 08:10 PM   #11
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Originally Posted by john61ct View Post

Your mistake with the bulbs is assuming the nominal watts rating is the actual power consumed. Not the case, need to measure with an ammeter, and be able to vary the consumption in order to keep the amps rate as constant as possible.
Ummm.... I'm sorry, but are you saying a 60 watt incandescent light bulb does not consistently draw 60 watts?

I find that nearly impossible to believe.
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Old 08-06-2019, 08:35 PM   #12
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Ummm.... I'm sorry, but are you saying a 60 watt incandescent light bulb does not consistently draw 60 watts?

I find that nearly impossible to believe.

Oh boy not so sure I want to jump in but yes a 60 watt incandescent bulb that the package says uses 60 watts is for real 60 watts, maybe give or take a few watts depending on voltage. From a purely scientific perspective those few watts will make a small difference, but not real world use for our purposes.

I have seen some "power saver" bulbs that claim 60 watt that only use something like 50 watts, and are actually lower lumens, so they are really 50 watt bulbs sold to "save" energy, of course with dimmer light....

This is all assuming incandescent bulbs.
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Old 08-06-2019, 11:38 PM   #13
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You’re right. I didn’t read incandescent.
What is the model you’re using. I’d like to look up all the input output specs.
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Old 08-07-2019, 02:32 AM   #14
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Why are batteries expressed in Amp hours instead of Watt hours?

By specifying voltage separately, the unit of 'Amp hours' allows convenient recalculation for different series/parallel combinations of batteries, as well as easier calculation of battery lifespan (measuring load current is easier than load power).

Amp hours relate to the basic chemical reaction of the battery whereas Watt hours are much more affected by state of charge when charging and discharging and by rate of charge and discharge.

In a LFP battery the Ah efficiency can be 99.5%+ but the Watt hour (energy efficiency) varies between 70% - 90% depending on various conditions and parameters.

A battery will vary its voltage across its charging / discharging range.

Charging:
Internal resistance x charge current squared = internal resistive losses which is totally wasted energy.

On discharge, internal resistance x discharge current squared = internal resistive losses
which is totally wasted energy.

In one case the waste energy is reflected by a rise of voltage at the terminal and in the other by a drop.

When charging, in the earlier part of the cycle the internal resistance is relatively low. The Ah put into the battery are largely recoverable AND the Watt hours also.

But as charging progresses, internal resistance rises, charging*energy*efficiency drops BUT charging*current*efficiency is still reasonably high.

Taking a LFP bank again as an example, when it is fairly new, the CURRENT charge to discharge efficiency is about 99.5%. As the battery ages this efficiency*INCREASES!*i.e. almost all the amps × hours put in can be taken out.

BUT the Watt hours put in and Watt hours taken out depend where in the cycle they are put in and how fast they are out in. Watt hours in the early part of the cycle are reasonably efficient but decrease in efficiency as voltage rises.

IOW, Amp hours more closely relate to the basic chemical reaction of the battery proper, whereas Watt hours are much more affected by state of charge when charging and discharging and by resistive and other losses which vary greatly by the rate of charge and discharge.

Simply put, the number of watt hours that can be taken from a battery will vary significantly based upon things like the rate of discharge; the number of amp hours that can be taken from a battery will vary less.

TL;DR Amp hours better specify what the battery stores and provides than what Watt hours do.
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Old 08-07-2019, 02:41 AM   #15
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The **current** is what needs to remain Constant when load testing a bank.

The watts need to vary in order to accomplish that since by definition Volts are changing constantly as you go from precisely 100% Full to 0% SoC.

The timing element should be also standardized, when setting benchmark at commissioning time - after breaking in protocols and period have created maximum Ah capacity - you want precision, as rate of decline in SoH is a very strong indicator of battery build quality, chemistry purity etc on the one hand, and the effectiveness of your care protocol combined with given usage patterns, in striving to maximize longevity, on the other.

Some owners don't care so much, not mission-critical use case anyway, aren't spending thousands on their consumable banks, don't mind just replacing more frequently.

But getting this stuff right is important for those that do.
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Old 08-07-2019, 02:50 AM   #16
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BK Precision electronic loads are tops, I've picked them up in great shape off eBay for 80% off the MSRP.

ZKE, ZKETECH EBD series are very reasonable.

Many quality hobby chargers include robust CC load discharging into bulbs or resistors, iCharger 4010 Duo being a good example.

Google keywords: Electronic Dummy Load Battery Tester

____
DIY hacks

https://hackaday.com/2017/02/28/beef...s-two-mosfets/
https://hackaday.com/2013/10/28/buil...electric-load/


cheap Chinese, many variants, can be paralleled
Banggood: http://voltlog.com/y/9lbrq
Ebay: http://voltlog.com/y/293qw
Amazon: http://voltlog.com/y/5a6be https://youtu.be/K-7kgfbH-eI
https://youtu.be/KYncNH8_m70

https://m.banggood.com/8-In-1-150W18...p-1248703.html

https://www.banggood.com/100W-DC-12V...p-1337352.html

https://m.banggood.com/150W-Constant...p-1255707.html

https://m.banggood.com/250W-DC-12V-D...p-1383823.html



https://m.banggood.com/150W-Constant...p-1255707.html
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Old 08-07-2019, 09:53 AM   #17
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I'd still like to know the model because I've yet to find a solar generator or all in one that performs anywhere close to a regular battery and charge controller for the same or less cost. Most $20 wpm controllers now do 30 amps and a good agm is about $150. Even mppt controllers are considerably cheaper than they were and provide far superior charging profiles and voltage input flexibility. The major limitation of most all one units is you're severely limited in expanding the system, or adding panels.
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Old 08-07-2019, 11:10 AM   #18
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Yes, there aren't any, all grossly overpriced and inflexible, much better off DIY to meet your specific needs.

Key failing is lack of a standard third-party replaceable internal battery at reasonable cost.

And crippled C-rates both charging / discharging.
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Old 08-07-2019, 03:49 PM   #19
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Old 08-08-2019, 04:33 PM   #20
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I'd still like to know the model because I've yet to find a solar generator or all in one that performs anywhere close to a regular battery and charge controller for the same or less cost.

The key word in that sentence is "yet."

It WILL happen.

Back when the internet started, lots of retail sellers were saying it was a gimmick, and they weren't going to fall for it. Nowadays, nearly every viable business has e-commerce.

I used to work in the film industry, and was an early adopter of video as a solid creative competitor for film. People fought that tooth and nail, said it would NEVER look good enough. Now, almost EVERYTHING is shot digitally. Those of us who played around with our crappy hi-8 cameras until we got something reasonably good looking out of them contributed significantly to that.

I may not be a super smart or technically oriented person, but I AM a highly curious one. And when offered not-quite-there-yet technology that will radically simplify my life - and is very inexpensive to boot - I'm going to be one of the people who tries it out. I guarantee I'm going to learn more about solar power by playing with this portable pwer station or generator or whatever you want to call it than I have in two years of forum posts about it.

People buying in to new ideas is what causes the new ideas to develop. Video is way cheaper than film. All-in-one solar setups are much simpler to understand and use for the average person than multi-part systems. You can argue that all you want, but the fact that, despite a relatively high IQ, I comprehend almost NOTHING of several posts on this thread is all the evidence I need. There is so much info I DON'T need that comes up every time I ask a pretty simple question about solar - like "Is this the right equation for watt hours?" - that I retreat, which is why I've had a bus for a year but solar power for only a week. The implication that I really need all that info to have a working system is just not true.

And thanks for the Will Prowse link. He is the reason I decided to go for it and get a "generator" to experiment with in the first place. He explains things in super clear terms, and he is totally open minded as things change.

PLUS... While I'm sure the setup I'm working on does not perform as well as the right battery and charge controller, the question is, does it perform well enough for ME? It's a pretty cheap solution, if so, cheaper, I'm guessing, than even the battery part of the "right" system. That's why I'm playing with it.
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