PTC heating - can it work direct on PV panel?

[racmaster]

i have some abundant PV panel, 18VDC about 150W used before with classical regulator to charge 12V leadacid battery... can i attach it directly to 12V PTC heating elements without regulator, just to act as: sun managed

as sun is up, heat is on, as it goes down, heat is off...?

https://www.aliexpress.com/w/wholesale-ptc-heater-element-12v.html

[bcroe]

A panel connected directly to a resistive element will only be matched for good efficiency
at a particular level of sun, possibly a level that is too low to be useful or never occurs in
the real world. It can work at quite poor efficiency if you do not mind wasting much of the
potential of your panels. good luck, Bruce Roe

[racmaster]

thanx, could you put some counting example pls? PTC is 60w, panel 150W, usualy doing not more than 100W in classical old - not mppt regulator and battery setup scheme.

what efficiency lost do we face if connected directly to PTC 60w x 2pcs in paralel/serie?

[PNPmacnab]

Do something for me, measure the resistance. These things can vary greatly depending on how much power id fed to them. Unfortunately, it works opposite of what you would like. Your panel is 18V and heater is 12V. One just may be the closest match.

[bcroe]

thanx, could you put some counting example pls? PTC is 60w, panel 150W, usualy doing not more than 100W in classical old - not mppt regulator and battery setup scheme.

what efficiency lost do we face if connected directly to PTC 60w x 2pcs in paralel/serie?

Check the MPPT voltage and current of your panel setup. Plug them into ohms law, and you will
get the optimum resistance heater to operate at MPPT. However MPPT is a moving target along
with the sun, so that heater resistance will rarely be a great match. Bruce Roe

[racmaster]

resistance shows at about 0.007 on 2k MM setting

my main target isnt efficiency of the panel, the only goal is to heat the ptc up to any temperature. which means, that i dont care, if they will work on 50% because of inefficiency of panel.

just if such a simple setup: panel-ptc will work safely or there is some security, burning issue...?

[PNPmacnab]

The 2K range won't be very accurate. 7 ohms at 12V would only be 20W if connected to a battery. Your numbers are off by a factor of three. So far off I can't really be of any help. My best guess would be to put two in series. A university study which was a little short on data indicated that for less than optimum weather conditions, almost 2X the ideal resistance gave better yearly production. There are some youtube videos on PTC by nobody with any real knowledge.

[racmaster]

if connected to battery, it takes about 5 Amp until it reaches target temperature, afterwards it goes down. as soon as u start pumping the heat away from the ptc, it goes back to 5 amps/12v. per piece.

[PNPmacnab]

That is what I said. 2.4 ohms is about 1/3 of 7. Two in series would probably give more daily output. One could possibly have higher output for two hours of peak sun

[racmaster]

sorry, i just dont understand. my basic position was: if there will be less sun, there will be less heat from PTC, if more, they (6pcsx60W) will take as much as panel is able to produce. if i will connect 2PTC, power from panel will be splitted to 50% for each. if 4, 25% for each. summary should remain the same. whats wrong on this?

[PNPmacnab]

Not even on another planet. Each heater is 2.4 ohm. Panel ideal in full sun is 2.1 ohm. So, this is a good match as far as a resistor. But that will put more power into the heater than it can take and heat out will drop. You don't have a resistor and will need two in series and those two in parallel, 2S2P.

[racmaster]

could yo put some numbers? what Watt can we get in 1S, 2S, 2P, 2S2P?