AC Charger on the Charge Controller Input?

[SirMichael]

I'm putting together a small solar system, 2-100w panels and a Renogy charge controller and a single 100AH SLA battery. I'm not planning on a lot of bright sun here in SE Minnesota, especially during the winter months so I may well need some supplementary battery charging for my 12v power usage.

However putting an AC charger on the charge controller output side (diode isolated) will require a charger that is rated for SLA battery (float, charge, etc.).

Is there any reason why I can't put an AC charger (about 15-16v) on the Solar Panel side of the charge controller, with some Shottky diode isolation to keep the solar panel power out of the power supply output, and the Power Supply output out of the Solar panel input. That way, the Renogy charge controller has full control of the battery charge/float voltage, and when the solar panel voltage drops to below the AC charger voltage, the AC charger would supply the input voltage to the charge controller.

I'm guessing that I'll use something like an 15 to 18v supply that would fold back it's voltage when the current requirements exceed the supply output.

Is there any reason this setup would be a problem? (I'm pretty good at designing hardware for the Shottky diode circuit and heat sink. I have some 30v/30A dual diodes in a TO220 case that should work.)

Sir Michael

 

[sunshine_eggo]

Many folks have tested/used their 30V/10A supply as the PV input to a MPPT.

 

[Rednecktek]

If you're just going with a single 12v battery, why not just clip the battery charger right to the battery? Your solar isn't going to care at all and no fussing around with diodes and the like.

Even the cheapest automotive battery chargers can handle SLA just fine.

 

[SirMichael]

Your suggestion to clip the battery charger to the battery is not right. The charger output would be feeding into the charge controller output. You need diode isolation. You can't put two power sources in parallel without isolation.

I don't want to have to worry about the charger doing the regeneration to the battery, but rather let the solar charge controller take care of it.

I'm hoping that I can put the supplementary charger on the charge controller INPUT.

Sir Michael

 

[timselectric]

If you have the power supply. Just connect it to the battery and set it at a lower voltage. Enough to get by on. But not high enough for a full charge. When solar is producing it will take over. And the power supply will remain idle.

 

[sunshine_eggo]

Your suggestion to clip the battery charger to the battery is not right. The charger output would be feeding into the charge controller output. You need diode isolation. You can't put two power sources in parallel without isolation.

They are diode isolated. Anything advertised as a charger HAS to have reverse current protection.

I'm hoping that I can put the supplementary charger on the charge controller INPUT.

Again, yes, and it's done regularly. You'll actually get more power out of it since the MPPT will allow it to operate at peak voltage/current rather than at battery voltage/current.

Here is a post by the owner of Midnite Solar on the subject:

Testing MPP Charge controller function with bench power supply?

Anyone know if you can use a 5A-60V DC power supply to test functioning of a MPP charge controller. I have a all in one inverter with charge controller that I am testing in my shop before shipping to where it will be installed in MX. Everything is working great but don't have PV panels here and...

diysolarforum.com

 

[zanydroid]

Is it advisable/economical to keep a high capacity 12V MPPT around to buck down high powered AC chargers for higher voltage formats down to charge 12v? Instead of keeping an extra set of AC chargers around just for 12v

 

[sunshine_eggo]

Is it advisable/economical to keep a high capacity 12V MPPT around to buck down high powered AC chargers for higher voltage formats down to charge 12v? Instead of keeping an extra set of AC chargers around just for 12v

I don't think an actual charger will work. I was clear in specifying a power supply. Chargers tyically require a battery voltage to be within an acceptable range before they will engage. The MPPT does not necessarily supply any equivalent "battery voltage" to the PV terminals, so a higher voltage charger likely won't know what to do.

 

[SirMichael]

As I mentioned, my concern is the correct tending of the battery. The charge controller specification says that it handles the "Bulk, Boost, Float, and Equalization" charges. If I put a battery charger on the battery, then I may well defeat the variation required for tending the battery.

I'll hook it up and try it.

Sir Michael

 

[zanydroid]

You can parallel multiple chargers as long as they semi-agree on the charge cycle shape and voltages. EG, CC current don't need to match.

If the charge cycle shape 100% matches (or close enough relative to tolerances), that is a standard config.

If charge cycles don't agree then I think some weird stuff may happen. Not sure if that means charging becomes less reliable, some chargers drop out, or you start a fire.

(Went back to your first post. Looks like you are aware of that)

 

[sunshine_eggo]

You can parallel multiple chargers as long as they semi-agree on the charge cycle shape and voltages. EG, CC current don't need to match.

If the charge cycle shape 100% matches (or close enough relative to tolerances), that is a standard config.

If charge cycles don't agree then I think some weird stuff may happen. Not sure if that means charging becomes less reliable, some chargers drop out, or you start a fire.

(Went back to your first post. Looks like you are aware of that)

Charging from multiple sources

One can have as many independent charging sources running concurrently as they like provided they are programmed properly for the voltage of one's battery bank. Examples (some or all at once, even multiples of a single type, different brands, etc.): Solar PV via MPPT Solar PV via PWM AC-DC...

diysolarforum.com

 

[Hedges]

You can't put two power sources in parallel without isolation.

You already did. You put one source (SCC) in parallel with another source (battery)

I'm hoping that I can put the supplementary charger on the charge controller INPUT.

Sir Michael

Might work, have to respect voltage limits.
Don't know how your SCC will behave. Some have "constant voltage" and "turbine" modes in addition to "solar MPPT"

As I mentioned, my concern is the correct tending of the battery. The charge controller specification says that it handles the "Bulk, Boost, Float, and Equalization" charges. If I put a battery charger on the battery, then I may well defeat the variation required for tending the battery.

If your AC charger has lower voltage than SCC, it should help with bulk and prevent over-discharge, but will drop off during absorption.
"Equalization"? Do you have FLA?


My equipment (SMA) primarily charges from AC, including AC coupled PV. It can accept DC charging, either with a shunt so it can keep track of current in/out of battery, or with a data bus so it not only sees current, can also control voltage and charge phase of DC coupled SCC.

 

[zanydroid]

FWIW I've been looking at a lot of chargers lately, and 10-20A SLA (or even multiple chemistry) chargers are really commodity these days on Amazon.

That said I don't know how configurable they are to match a SCC's charge profile, or how configurable your SCC would be to match a commodity charger with minimal configurability.