Getting what You Paid for using Science
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- čas přidán 17. 01. 2021
- Testing a 12V 800W water heating element. These are great to use for resistive loads. When doing an Ohm's Law calculation you can determine how much resistance should be in the element. This is 12 volts, 800 watts, which should draw 66.7 amps. But in my testing I was only drawing 150 watts. What happened?
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Affiliate Link to 12v 600w element: ebay.us/Qsv7JA - Jak na to + styl
As you know, water heater elements are purely resistive. That means that the only thing input voltage changes is the amount of power it can consume. At the $25 price point you are likely getting either 120vac or 240vac water heater elements that have been repackaged for lower DC voltages. If you can find a 5500 watt (common size) 120vac element, locally or online, it will put out roughly 600 watts from a 12.8v DC source. And it will likely be about half the price, as you save the middle man markup.
@@calysagora3615 search for Ohm's law calculator (fill in the voltage and resistance) :)
@@calysagora3615 Look up Ohms law. V=I*R (Voltage=Current*Resistance). In your case I=V/R.
@Jan Lenz Power is linear to voltage when current is kept constant. So you are correct under purely resistive loads that power will quadruple for a doubling in voltage.
If your using a constant current system the power can be calculated in a linear fashion.
It helps to outline ones assumptions and correct those rather than simply stating someone is wrong. I.E show them under what conditions they are wrong because under diffrent conditions with proper assumptions they may be correct.
@@nocare, there are no assumptions. Aspendell clearly stated the heating element is purely resistive. Therefore power is E^2 / R. Cut the voltage by 1/10th and power is cut by 1/100th. Now Jan assumed 12.8, not 12.0 volts, so they came out with 62.77 watts.
In order to have both elements in series, thus having max resistance, you should remove one of the plates i think, and hook the power to the ones that are not connected
I like your attitude. Giving vendors a chance to make things right it’s always a good way to go in business.
Thanks for the video Its looking forward to seeing the results and if the next ones are up to spec.
I appreciate your attitude towards the situation. Refreshing. Hopefully the next set work as advertised.
Kinda but letting people get away with selling us junk and unless you know what you are doing and call them out you would just have a very poor performing water heater
Testing to validate specs is always good - especially when dealing with Chinese stuff. Thanks for sharing your testing methodology - looking forward to your next project.
When you measure such a low resistance with a DMM, you need to zero out the resistance of the leads. The leads have more resistance than the element itself. A better bench type meter will allow you to make 4 wire measurements using 2 force leads (forcing current) and 2 sense leads (measuring voltage). However, your water bucket power test did seem to indicate that the element was weaker than expected and the wire gauge was pretty huge, so the poor result cannot be blamed on wire loss in that test. You were right to return them anyway.
Like that you are giving them another chance. Hope its as advertised this time
David,
a cold resistance measurement will give x. However the only way to know the resistance at operating temperature is a voltage and current measurement and calculate. All resistive conductor's resistance varies with temperature, most are positive and as temperature increases so does the resistance. At switch on there will be a surge current which drops off as the element heats up.
One other point to remember is that multimeters are rubbish at measuring low resistance.
I like Dave's attitude here giving small businesses a quote un quote
" A Fair Shake ". 👍👍👏👏💯
...just wanted to let you know that my new 600W 12V heating element came in today. The resistance tested right (2.4 Ohms, although I know some resistive loads can change dramatically with temperature...this doesn't seem to), and when I connected it to my 12v 62A power source, I FINALLY GOT 50 a @ 600W. I got it through Amazon and it was a 'twin' for the fake.
Thanks for the video!!!
I wrote 2.4, when I intended to write 0.24 Ohms....
Thank you, sir.
heya totaly agree and that's why it's good to do your own test's and calcalations
I appriciate how you handled that.
I just got me some 12v 600w im going to test them like you are
Thank you,I had the same problem!
Love your content so darn much man you rock honestly
Thanks for the video! I'm in the process of setting up a 12v load diverter on my sailboat to heat water for showers and washing. Now I know that I might not get what I order and to double-check the resistance of the element before going to all the trouble of installing it.
I=E/R "More than a good idea, it's the law"
Best regards from Key West,
Capt. Blackheart Charlie
We need more guys like you in society Dave. You and your family are awesome. Love the videos!
Think you for the video
great video, thanks !
Looking forward to the 600w video.
You should use Kelvin contacts (4-wire) when measuring low resistance.
What about the current drawn
An Unintended Consequence - While watching this video I saw you measure a DC current with the meter clamp and wondered how that was possible. My experiences with clamp around ammeters years ago were limited to AC circuits where the varying flux induced a voltage in the clamp coil. So I used Google Search and, thanks to Fluke, learned about Hall Effect sensors for steady state flux measurement. Seventy-five years old and still learning stuff all the time.
Always with cool stuff 👍
I agree with the other poster. These sound like 1500 watt elements because 10 * 12 volts is 120 volts, and 10 times 150 watts is 1500 watts.
I see you actually verify what you purchase, and that IS a good thing. So many would have never ever done that. And that is because the typical consumer just doesn't understand such things... Thumbs Up! Math doesn't lie!
Great video!
Wow, that is very poor of them to have sold a product they "just got in" and didn't do any testing on. I like your attitude towards giving them another chance, but I feel that wasn't a mistake... We shall see, keep us posted on how the new element works!
I dislike his attitude of saying 'hey you bent me over once, how about another go?"
Name and shame for the benefit of all, and find someone more reputeable to indirectly advertise.
True, but sometimes the buyers aren't technical, they just buy relevant stuff people are looking for from wholesalers or discontinued bulk lots and have it for sale.. A 2nd chance if they don't seem scammy is fine for me... I'd do it. If they fought back when given scientific evidence and didn't even bother with a different unit then they are shady.
It's also possible someone jumped the gun and posted them on ebay before they were supposed to. David did say they were on the ebay store and not the website store. This could have been an honest mistake.
The seller should have let you keep them and then just send you new tested good ones.
?@@volvo09 Some thing called "incoming inspection" NO CHECKING? The cost of not checking is WAY lower than shipping a bunch of wrong goods.
I ordered a 12V/300 watt element from them. I plan on putting it into a 18 gallon barrel inside a 30 gal barrel surrounded by closed foam insulation!!
So about 30 volts to get closer to the watts on that one. Seems like a lot of amps to try and eat power at 12v though.
great content thanks
Great use of tools to verify the specs! And great attitude about it. What is the ammeter box that you were using?
The meter box I built in a previous video. czcams.com/video/sJ-sy8Osqr0/video.html
@@DavidPozEnergy Thanks! Sorry I missed that one.
*Chinese watts are only 20 percent US watts*
And only last 20% as long.
Watts you sayin!?!?!
@@widewinger1454 nah, those are made to spec for USA importers.
Like amazing claims on stereo speakers/amps.......multiply x the date next tuesday and whack that on the packaging.....
@@nickab9719 On paper maybe.
I hooked up 2 full sized solar panels in series. Then wired them directly to the bottom heating element in my home hot water tank. I used the rated voltage and current of the panels to figure the panels resistance. Then found an element that was close to the same resistance. Heating elements do not care if the power is DC or AC or the voltage as long as the voltage is not too high. The top element made sure that the water was up to temp. Did not have any switches or controllers. Wen the sun was shining it heated the water. Wen the sun went down it did not heat the water. I used some big 50A plugs to connect the element to the panel wires. It worked really well in the summer. not as well in the winter.
I'm pretty sure they sale the elements as maximum wattage. So if you apply 24v or 48v, you'll see more wattage
The battery controller meter concured with the multimeter. Right there is the confirmation before going anywhere else. 1.1ohm suggests that the element is a higher voltage rating, which equals incorrect product sent.
Thanks for this wonderful insight. Please I have a steam boiler of 24 liters and 3 phase, producing 6 bar pressure.
Please what if I changed this connection to single phase, will I I still get 6 bar pressure?
Thanks.
Max power point is when the resistance of the source equal the resistance of the load.
Most heating elements increase resistance as they heat up. Old fashioned lightbulbs made of tungsten changes resistance dramatically.
I don't know the temperature characteristics of these type of elements. I suspect they are made of tungsten and the resistance will increase as they get hot.
I enjoy your videos. I would like to see if you can run your heating element in a bucket to run your garage under floor heating.
Low wattage elements will be slow but very useful in a solar-powered RV like mine.
When measuring low resistances, it is common for the meter leads to have higher resistance than the resistor. Low resistance is often measured with a "4 lead ohm meter" setup. Use a constant current lab supply and feed your load with 100mA or 1A depending on the load. Measure the voltage across the resistor and calculate the resistor value.
EG, your element at 1 amp is close to 1 volt, so it would be 1 ohm, or if fed 100mA, would be 0.1 Volts = 1 ohm. With this method the real 800Watt element at 1 amp would have 0.18 Volts on the terminals and dissipate 0.18 watts, so the test would not heat your element for the test.
DUH! test leads are 4th order in resistance, therefore, nobrainer. GEEZ.. over-complicate a simple thing.
not necessary he measured the actual amp draw. P=IE, simple as pie.
Check your math at 48 volts. I think they sent you the wrong ones.
This. 100% there's been a screw up in the supply chain somewhere (whether it was by who he bought them off, or who they bought it off in china) and he's got a 48v element.
Doesn't help they normally don't mark anything at any point either.
I think they provided 120v 1500 watt elements instead.
Ya but at 1.1 ohms that's like 2000 watts it's closer at 24v it's over 500w
@@richardowens9061 at 120v it would be like 13,000 watts
It is advertised as 12v 800w
Hook up the elements in series then take a resistance reading. Meters like that do not do well near 1 ohms. If each element is 1 ohm in parallel they will be 0.5 ohms. in series 2 ohms. Your meter will give a much more accurate reading at 2 ohms.
That’s true - better to do what David did after - measure the current and voltage.
I agree that these meters are not great at low resistance, but I don't believe he is getting bad readings as his power meter was showing 1.1 Ohms and ohms law calculations based on voltage and current from the power meter also point to about 1.1 ohms. No point in doing more work to get the same answer as it has already been verified 2 times.
Ya like D said I have noticed never getting real low readings and that would probably give you a little more accurate number but he tested it and it's right there in line with his measurements
Resistence varies with heat, if that is measured in cool 1.1ohm, in hot it will get higher resistence.
Hi anyone know if it would be safe to wrap stainless steel pipe around an element? Trying to get a little bit more heat in my circulating shower
They usually have the specs printed on them. I ordered a bunch off AliExpress straight from China for the DMPPT450 setup, and if you can wait a month for them to arrive, I can recommend going that route as they're significantly cheaper and were exactly what I ordered.
Thank you Noel. Was there a supplier name you went through? Or a link to help the viewers?
@@DavidPozEnergy You bet. Here's the link to the ones I used for the DMPPT450 project. There are other wattages and voltages listed by the same seller. Also if you do some math you can create combinations of them using series or parallel strings to achieve the desired voltage and amperage. www.aliexpress.com/item/32549842825.html?spm=a2g0s.12269583.0.0.26ed528bfvxLub
It's DERNORD Official Store #1862595
Thanks for trying Noel. That link is specific to your past orders. I can't get it to work for me. Maybe, what's the sellers name? I can find it and post a link.
@@DavidPozEnergy Thanks for letting me know. I tried a different link and updated my last post. Let me know if it still doesn't work.
Works great. Thanks for sharing
Ive similar ones, they can be 24v 600w with 2 elements in series with or 2 x 300w in parallel - depending how the brass fitting on the end are configured - so watch out for that as mine came with the brass connections for parallel / 24v
These are wired in parallel, you would have to remove one of the plates to wire it in series. If the resistance on both strings are kinda similar, the resistance in series would quadruple and the power output would drop to P=U²/R= 32,7W
i was looking at buying a 12vdc element recently and came across a website that explained possibly what is going on. Apparently is all too common practice for resellers to buy standard AC water heating elements and sell them as more expensive DC elements. Apparently all heating elements are marked for their voltage and output, dishonest sellers will melt these markings to make them illegible. Check your elements and look for the markings or the melt plastic which was used to cover their tracks.
I want hopefully we can get an update on the 600 watt heaters to see if they are as advertised
Just wondering what youre using to keep the heating ellement away from the bucket melting
Before you said "we have been running for 10 minutes" I was gonna say "just wait until you let it sit for a bit... as a resistive load gets hotter the resistance increases so your power will decrease" lolol
This is only true with some resistive loads, some others will have a negative temperature coefficent (NTC) and as they get hotter their resistance will decrease, which often leads to a thermal runaway. You can test it with a small carbon rod which has a NTC and when connected to a power supply or battery will start conducting slowly but eventually conduct more and more until it burns up. It is a fun experiment as right before it burns up all the way it will start glowing bright white, easily enough to light up a room
@@josephsvensson6637 now THAT sounds like a YT video idea to me!
Can you use the same pv panels for the dc element and the inverter?
I love your videos
OOOOHH YEAEE EVERYTHING IS SO BEAUTIFUL
I'm sure you checked the jumper plates on the fitting for correct connection.
would work pretty good for a 24 volt setup at 500ish watts
getting into vlog a bit , what kind of camera set up are you using David?
I'm noticing that it's getting more and more common to sell items bit off the listing. I assume that they will get a ton of money on customers not technical enough to notice it. But now 3 times I have encountered this, thay all seem to go the same route and try to buy you to be silent.
I am vaguely remembering something I encountered decades ago and haven't used since, fair warning. One of the tricks with transferring power is impedance matching. The resistance of the current source must equal the resistance of the load. Since you can't put an ohmmeter across a battery or solar panel, you look at its short circuit amps, and derive the resistance from that and the voltage. In essence, this is the same trick you use in a mechanical power train by shifting gears. Something to think about; I'm up late and can't be arsed to suss out the details.
Well that is a very different thing you are talking about now. Impedance matching is used when dealing with RF signals to reduce signal reflection from the load. In this case we are talking DC and the load is all resistance (no immaginary part) so signal reflection is not an issue. You don't want any resistance in the source ideally. If your source has the same resistance as your load half of the heat will produced by your source and the other half by the heater.
You have a heater whit 2 heaters in it. the copper plate in between wil put it in serie or parralel.
I think it is on serie, so both heater wil get each 6V that means both heater are 0.5ohm each, if you change it to parralel than both heaters wil get 12V and the resistance is changed to 0.25ohm in theorie.
Than the power draw changes to 800watt.
The second question is than wil the unit be able to resive and hold the 67Amps or wil it melt because of the high current
One thing to consider that has not yet been mentioned here is that power ratings for electric components are often a maximum. Meaning that exceeding that rating will likely damage or shorten the life of the component. The actual power dissipated (heat) will depend entirely on the voltage applied and the resistance of the element, which will change a bit (increase) as it heats up... Yes, the vendor likely sent Dave the wrong element, and the resistance should be specified by the seller.
were these sold as 800w electrical draw or 800w of heat output
I'd be into a low wattage 24v dc thermostatic controlled one, like the 240v ac 3kw item found in my house. It'd make a useful dump load.
How low do you want to go? If you take the 3kw elements and connect them to 24v they will be about 300w.
@@TrackGeeks resistive load (heater) rated at 240V 3000W will take 30W at 24V, not 300W (P=U^2/R)
You could just get more of those and put them in parallel. At least if you have more of them the chances of them heating up will be less and as a result of the banks higher power handling they will have a steadier resistance.
What problems would I have connecting 600 watts of solar directly to a 600w 12v heating element in heat storage tank besides the possibility of overheating? Skip controllers, relays, or thermostats.
I understand that they can get things wrong, but a simple multimeter check at their end would have resulted in a better outcome for all who have ordered them and the company itself. Thanks for the heads up David.
What collar did you use to put that in the bucket?
Nice
Hello David on water heater element which is the positive or negative terminal s please has I'm trying to make hot water
Water heater elements don't have a positive or negative side. They are simple resistors. I can hook my positive or negative to either side.
Hi David. Great you make this public. Yes, good to give them another chance. On the other hand, they should test the products they sell! In this case its such a simple test, as you just demonstrated!
There are so many 'cowboys' out there making false claims on what they are selling - great you are taking it to the public. Cheers
Are they paying for return postage? If I wanted to simply return it, are they going to not only refund my payment but also the s/h fees?
So many people seem to be willing to bend over and take it from retailers, as if there aren't other reputable sellers out there...
You got a 24v 600w heater... at 12v it is only 150w... if you double the voltage the current doubles so you get 4 times the watts...
Good about the video!
But, why someone has a wall panel tools that has so much hammers, instead diversified tools? Hehehe!
You won a follower guy!
I used to be known on the jobsite as "the guy with spares". I was always happy to lend out tools, even though that didn't happen often. Hammers, tape measures, pencils, and saws I always had a plenty.
You were right because I’m at Mater it says 01.1 I think I trust your meter and that other meter more than I would eBay.
When I was working for ebay seller. He was writing Tested, assuring you that it it as advertised. But no one ever touched the item for testing because time is money. Not every buyer will notice, chance that flaw will not be discovered is high. When you read tested - mostly not tested.
One of the only ways to really protect yourself when buying general Chinease made products outside retail channels, is to find a forum or similar place where people have already bought and tested whatever widget you want.
There you can find the actual specs, and sellers that seem to have at least some reliability.
And even then, oftentimes those known good sellers will switch to a model they can get a few pennies cheaper from someone else, and restock with that model for a short-term profit bump.
Then of course, people find out that newer model is not as good as previous, and seller see's his demand tank.
Chinese especially can't seem to control themselves from killing the golden goose, this happens continuously...
I need some doubt please told for me
Is it likely to be a pure resistive load? Don't they have coils inside?
I have one of these to heat up an outside shower in my camper, it was advertised as 150w. I actually cheat a bit and run 24v through (cheap enough that if I burn it out, ill know not to) but have probably had it running all told for about 15 hours, and yes, this isnt to make a hot shower, just luke warm :)
Maybe your heat loss is too high to get it warmer with only a 300W load.
Good
Ahem. They are also as often listed in terms of current draw and N volts. You aren't really very interested in watts, you're interested in amps of current. It's even straightforward to translate volts / ohms / amps because they directly correlate to each other.
When measure low ohms 4 wire is best, or use current - voltage drop access the elements
You are not measuring from like a display on a power supply it's just the multimeter that makes no sense really I mean a meter is not going to have any way to hook up 4 wires to a multimeter
@@james10739 In a 4 wire ohm meter setup, you don't need a 4 wire meter. You need a regulated current source and voltmeter. This test would use a bench supply set to provide 1 amp. The 800Watt element should have 0.18 ohms of resistance. At one amp, the terminals on the element should have 0.18 Volts, easily measured with a DMM to 3 significant digits. EG 180mV. His element is about 1 ohm, so 1 amp would provide a measured voltage of 1 volt, or with a 3.5 digit DMM, 1.000 volts at 1 amp.
www.circuitsdiy.com/low-resistance-measurement-method/ I have to regularly repair equipment and verify the value of 0.01 ohm resistors used in current metering.
Heard about you from will Prowse. Looking forward to watching all your videos. I just bought 9 x 230 watt 24 volt (used!) solar panels and now I’m trying to figure out how to put together an entire system-also buying all used components. Wondering if there is anything in particular I shouldn’t buy used. I have lots of thick copper wire from wiring a hot tub and and from wiring a kiln and also a couple of gfci’s. I never hear anyone talking about using gfci’s on solar systems. Is there a reason? Can I re-use these? Thanks. It seems from wills book I have 2070 watts in panels so I have to have a 2000 w inverter but thought maybe I should get a 3000 or would 2000 be okay? Also I think the mppt should be 85 amps...and the batteries I was going to make from scratch, but I don’t know how much battery to make except I think it has to be 24 volt batteries and I should get at a minimum 2 x 100 amp 12 volts and wire them in series but that maybe it would be more appropriate to make 4 x 100 amp 12 volts and then wire them in 2-in-series for 24 volts and put the 2 sets of two in parallel for 200 amp hours x 24 volts or a total energy storage of 4800 watt hours. Have I calculated this correctly? One thing I am not sure is: I could only get 9 of these panels. Is it okay to use all 9 or should I only use 8? Later I would like to add some wind, and I’m keen to experiment with wind driving a couple of small flywheels I scavenged. Is that crazy? And I wanted to use any dumps to heat water and my living space (will be off grid as I have to move my RV somewhere else by May 1st. Also - is it okay to have the temperature fluctuate for my lithium batteries from 50 F at night to 75 in the day? Thanks for your comments and suggestions
Hi Kerr FamilyLaw, Thanks for checking out my videos. Most of my stuff I buy used, or on sale. You asked about anything to not buy used. I'd probably say safety devices need to be bought new, such as fuses and circuit breakers. But otherwise, I've had used equipment that still works fine.
Gfci, I have gfci outlets that work just fine with my off-grid system. But my system is grounded (ground-rod) so you might have them not work if you are doing a non-grounded system.
I have not read Will's book, so I don't know what you are talking about. Wattage of panels does not dictate wattage of inverter. There is a relationship between wattage of panels and wattage of charge controllers, but it's in-direct. It's more accurate to talk about maximum amps, not watts. For example, when I started I had a 4.4kw solar array with a 3kw inverter in the same system. Not relevant since my charge controller was what tied in my solar array. Today I still have the same charge controller and same 4.4kw solar array, but I've changed out my inverter for a new 12kw inverter.
Hi David! Are you going to do some experimenting on the dmppt450? I'm waiting for that one!!
No. I almost made the leap to test that, but it turns out you need 20v panels, and my panels are 24v. I checked with Electrodacus and he confirmed my panels wouldn't work.
Was wondering if the resistance decreases when heated as some materials change resistant with temperature? Just covering the bases. I came across the same similar issue here recently.
Generally speaking (and true of the water heaters I have tested) the resistance goes up a little as they heat.
@@DavidPozEnergy TY
Hi. I tried to connect dc 48v 1500w water heater element, and 3 panels 450w×44~50v in parallel... between them 32amps circuit dc circuit breaker ... distance between panels and element around 30m .. cable size 2×6mm ... volts received around 44v ... after putting switch on : voltage drops to 1 to 3 volts ... what's the problem? Thanks
u have to calculate the ohms,,,,is not working like that,,,try them in series connection and change the resistance to 240v x 3500watt and u will make it if no other problems appears
What are you using now for hot water since its been a few years on most of your testing? Im on solar except my hot water heater.
I have a solar hydronic system which heats water directly. That is my pre-heater. Then it goes to an electric tank, which only turns on if the solar tank is not hot enough. The electric tank runs off my inverter.
Did you measure the voltage at the terminals to confirm that you were actually delivering 12V to the load? Your lead resistance may be part of the problem.
It just needs more voltage!! The watts will go up, until it stops! Ha-ha..
Are you sure these were not setup for 24v? Can you test each coil without the bars?
I like these DC elements with dual element, because I can play around with the resistances to get different power levels.
Can't get nothing past the Poz
70Amps from a car battery long enough to heat a bucket of water sounds plausible to you? Will the battery survive?
I think they provided 120v 1500 watt elements instead.
An idea : what if you pass the water pipe, going to the tank or going out of the water tank, through a dc induction heater that works on solar panels? Will that give instant hot showering water maybe!?
The terminals look like they can be swapped between serial and parallel. Perhaps try it in the other configuration.
You are right. I showed it in parallels, which is how it's supposed to be for the 800w rating. But I've gotten this question enough that I'll demonstrate the series connection in my follow up video. It will draw less watts in series.
are the elements hooked in parallel or series series well be more resistance keep up the good work
The brass bars connect the elements in parallel.
would be best on 36V... old grid tied panels.
1R. 12v. 12A.
12x12=144
X1=144. yep. 150 watts.
36v/1R
36A.
1296W...
theyre immersed. theyll take a bit more. plenty more...
or you just ignore all of that and buy nichrome wire by the roll. what will glow red or melt in the air will stay cold in water.
it doesnt need to be insulated, its still more conductive than the water.
Hi David, in this country 🇬🇧 we call it not fit for purpose 😔
If its 12V elements 800W look for mobile home - camping gear that has internal elements of suitable power, then obtain parts list and order that part, 👍
To be honest elements should be stamped 1kw 2kw 3kw 800w etc
Look at manufacturers that make only elements & if possible buy from them 👍
Or obtain their suppliers,
Don't go for general suppliers that just buy in from China & double up the price,
Buy from China or HK or Japan directly
Philip D 🇬🇧
what did you use to seal the inside of the bucket?
I didn't do anything to seal the inside of the bucket.
Great attitude, give them a second chance!! Nice! Congrats!
Thx. Like # 770. Did they remove the ad from eBay?
Hey Dave. Im asking a question.
Wouldn't a 45volt 800 watt water element be better ?
Been watching ya channel for ever. Davi b here from Ausie
Depends on what you want to do. I want a very low resistive load for bench-testing. I have some videos coming up where I want the 12v version. But if you have a 45v battery (or 48v, or 24v) and want to buy a element to match, then great. I personally have a 48v battery bank, so If I wanted to heat water directly from the battery I'd buy a element rated for that. Sometimes you can use 230v elements too, just depends on what your goals are.