Injecting DC current from a AC/DC Transformer into the LOAD controller possible?

[emulator64]

Hello,

I am new on this and on here . I tought i could get help on this. Is there any problem in connecting a 220v AC Current (Europe) to 24 dc Current to the Output load of the KID MPPT Controller to inject power if my battery and solar pvs are not enough?

This way all the 24v devices installed on my solar circuit would get power from the solar installation and when there is not enough power the transformer connected to my Home AC would provide the power when there is not enough power on batteries or solar panels.

The dc ouput of the transformer is not more then 12 Amps, the solar panels are max 15 amps. So the KID supports until 30amps it would be no problem?

The principle would be the same as connecting two transformers in parallel, when one is no more enough to provide more power.

Thank you
Peter

[boB]

Hi Peter

No, that would be WAY too much voltage for a Kid system.

Also, the input of the Kid is made for solar PV and not any type of grid impedances.

I would buy a separate battery charger and connect that to the battery and then it could help keep your battery charged in lower solar times.

[emulator64]

Thank you boB. It is not to connect to the PV Input of the charger. This is a usual FAQ many out there ask for, to connect a dc power supply to the PV or Battery input of the charger.

What i meant is to connect it in parallel to the Output/Load of the controller. The parallel connection would not add more voltage but more amperage right? And it would be to the output, so it would add to it. Its because the load output is from where all the power is consumed and i would feed it with more power

I would connect the out of the dc power supply to the out of the charger just to add current to the circuit.

[boB]

Not exactly sure what you mean by

"I would connect the out of the dc power supply to the out of the charger just to add current to the circuit."

What power supply ?  Just a 220 VAC to 24V DC power supply ?   The sentence(s) just before that sounded a bit different in intent   

As for connecting rectified grid to the input of a PV charge controller, we do not support that.  However, people have successfully done that.

[emulator64]

Yes, transformer (connected to the normal electric power at home)  of 220v AC  to 24v DC to the 24v DC load output. is this a problem?

[mike90045]

Your AC transformer needs to be converted to DC voltage after it's been stepped down.   

You CANNOT inject DC into a transformer winding.

If this is a transformer based DC power supply with a 26-28VDC output, you could connect it directly to your 24V battery. 
If you connect a 24V supply to a 24V battery, the supply will support some loads, but the voltage is too low to recharge the battery which needs a bit more than 26V DC before charging can begin.

[boB]

Yes, you could step down the 220VAC to somewhere around 24VDC but you would have to make sure that the voltage does not exceed whatever the high battery charge voltage would be.

What I would do, and this would be only in a pinch, when I really didn't have another way would be to use a variac to adjust that DC output voltage so that it was limited and then apply it to the battery.

If the difference in DC voltages is high enough, say several volts, the current will jump up when you apply it so I would maybe first  apply the voltage at the same voltage as the battery and then slowly watch the current and voltage as I raised the variac's adjustment.  Just know where on the variac dial the DC voltage will be the limit.  Also, beware that the AC line voltage can change somewhat over time.

[emulator64]

Thank you all for your kind answers. But at this time i am not worried about battery charging, because the battery is charged well by the solar panels. The problem is that the batteries have not power enough, because their are almost end of life. They still work for my less powers demand devices on the circuit. But i still want to add the power of the LOAD circuit and add the 220V/DC 24V POWER to the load directly, so when the power is not enough it will get it from the 220v/24dc power supply. At the same time it would still get advantage of the remaing power given from the batteries and solar panels therefore sparing some of the power 220v/24dc. I am sending a small draft image so you can see what i mean.

[boB]

Oh, OK.

I suppose this all depends on the capability of the load control circuit in the charge controller.

And is the load inductive ?  If it is very inductive, you can get some pretty high energy and high voltage spikes when the control turns off the load.

[emulator64]

Good point boB, both the KID and the transformer have coils in it. I also have fans on the circuit wish are inductive. The result would be a very high voltage pulse. The capacitors inside them could become shorted. It could destroy MOSFETs or other solid state switches, and switch and relay contacts aswell.
What would be the recommended solution for this? A surge protector perhaps?

thank you

[boB]

Good point boB, both the KID and the transformer have coils in it. I also have fans on the circuit wish are inductive. The result would be a very high voltage pulse. The capacitors inside them could become shorted. It could destroy MOSFETs or other solid state switches, and switch and relay contacts aswell.
What would be the recommended solution for this? A surge protector perhaps?

thank you

What you could do is add an external relay that is controlled by the load control. 

What that terminal does is to ground the load terminal.  So you could connect  a relay coil to that terminal and the other terminal of the coil of the relay to the proper positive voltage.   For example, if you have a 24V battery system, get a relay with a 24 volt coil and connect one of the coil ends to the load control  terminal and the other coil terminal to the positive of the 24V battery.

Then connect whatever you want to the relay contacts.

Using a separate relay like this will keep any possible difficult load away from the FET transistor.

[emulator64]

I see, you mean connecting the negative load to a relay coil wish in turn, when the spike happens, connects to a ground terminal? I have the ground terminal from the kid wish is connected to a aluminum bar bolted to a cement floor. What type of relay coil could i use? Perhaps something like this:
https://www.hella.co.nz/en/technology/relays-and-flasher-units/elimating-voltage-spikes/