# Trying to make a circuit diagram from this

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#### AprilSteel

Feb 2, 2017
111
Guy answered my wish for a device to attach in the Photovoltaic input line of a solar system to move current into a water heater when the battery was full and there was sufficient energy coming in.

He answered this way and I am trying to work up a circuit.
He's moving atm and won't be contactable for a week.
Don't have a scanner working yet. But I understand how the TL494 pulses the Mosfets but how it all connects up to the capacitor bank is the confusing part for me. I assume its NChannel mosfets . Plus I don't see 4 resistors ,one across each Mosfet =2?
There is only one method that is efficient for resistive heating. Storing energy in a capacitor, keeping that at a constant voltage and proportionately dumping into the load in pulses. There are many ways to do that, but they all follow that principal. Operating off lead batteries by a voltage switch should be avoided. There are other circuits using cheap China inverter boards on the internet.

A capacitor bank is needed and should be isolated from the charge controller with a diode. That will prevent tracking errors with a MPPT charge controller.

The easy way to do it it with a TL494, these are like 10 for $1. It has all the features you need. Just operates the inverse of what it is usually used for, turning off at a low voltage and on when it gets high. A resistor and capacitor for the oscillator. Voltage divider pot to turn PV voltage to about 5V. 4 resistors to drive the two FET. Two fet as the output switchers. These FET will be in parallel and you use two to get the resistance down so there is no heating. If you buy a 100A FET, don't use it at over 10A. Two get you 20A easily. They are cheap and no reason to use big heat sinks. Litle perf boards are 5 for$1. There are also thru hole TL494 driver boards cheap that a couple of traces could be cut on.Then a resistor and zener are needed to supply 12-15V.

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#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,615
We need a schematic diagram of your circuit, please. No way to decipher the circuit from your photo.

#### AprilSteel

Feb 2, 2017
111
We need a schematic diagram of your circuit, please. No way to decipher the circuit from your photo.
Please put your glasses on and read the post . I am asking for somebody to make an attempt at drawing a circuit . That is the whole point of my post.
You are a Moderator ? crikey

#### davenn

Moderator
Sep 5, 2009
14,043
I am trying to work up a circuit.

OK
we really need to see some closer up pix of each section so that individual wire connections can be identified
including the reverse side of the display
Without that it is impossible to do. Even with those pix, it's going to be quite a job

Dave

#### duke37

Jan 9, 2011
5,364
You must have had some sort of instructions to make the spaghetti.

#### AprilSteel

Feb 2, 2017
111
No in fact what I have is a quick post from an offgridder before he left to return home . In about a week I think . Then I'll get more . You have all the info I have in the above post .
BUT from whats above I was able to draft up a bit of a circuit, but I don't have a working scanner ? Hang on Ill snap it .

This is to transfer current from the solar charge controller only when the battery is almost full and there is sufficient power coming from the solar cells.

OK so the guts is the TL494.
Powered 5V from a pot on the cap bank (bank of supercaps I want to use 2.7v)
Oscillator on TL 494
Solar charge controller feeding capacitor bank through a diode
TL494 pulses two Mosfets in parallel
There is a resistor across each of them -don't get that yet
Bleed Resistor across caps
Mosfets I think would be NPN's but not sure on polarities at this point.
Guy says 4 resistors as if they are all 4 on the mosfets.

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#### AprilSteel

Feb 2, 2017
111
Geez help is a bit thin on the ground on this forum . Plenty of complaints but no action.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
12,615
What output do you expect with such meager input?

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,739
Seems we have all been down this road with this poster. Not worth to time to respond.

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