charge controller size

[Sir squeegey]

New to solar ,I have a small setup that I have been messing with
100 ah sla batt.pwm charger (started with incase I messed up would not be out very much.)my question is wanting to goto mppt charger my solar panels pruduce 7.5 to 8 amps.would a 75/10 victron controller be ok with my small setup.

 

[Samsonite801]

Before you purchase a charge controller you need to understand what max PV input voltage is and why it matters in selection of an MPPT SCC...

You will need to know:
-How many panels you have
-What is the Voc and Isc of the panels
-What is the coldest temperature you see in your area where the panels will operate
-How will they be wired (series/parallel/combo)
-Do you ever plan to expand the system

Search for threads about this topic here, as there is lots of info about max PV input spec...

The general idea is you want to wire the panels optimally in series in order to get the Voc rating up closer to max PV input specs without going over, so you are up some order of magnitude above battery charging voltage (so the charger has plenty of flexibility in finding maximum power point and still having the voltage high enough to charge the battery bank). Also, the higher PV voltage allows for smaller wire which leads to cost savings in wire runs.

Feel free to ask more questions, but we need that info above in order to be able to provide more detailed recommendation back to you.

 

[Sir squeegey]

I have 2-12v 100 watt panels wired paralell that produce about 7.5 to 8 amps, I will have to check on the other things you mentionednot plannong to expand,it is a small setup for 4 trickle chargers and couple lights wwhen needed in a small out building

 

[snoobler]

Welcome to the forum.

Typical 12V 100W panels have a Voc around 22V and Vmp around 18. 2 in series would be well under the 75V limit of the 75/10; however,

200W/12V = 17A MAXIMUM - will typically be lower.

Thus a 75/10 (10A being the limit it can send to the battery, not the solar side) would not suffice.

A 75/15 would be the better choice.

 

[Samsonite801]

Yeah, and just to clarify, with 2 panels, you would want to wire them in series, not parallel, you will have better results, as it ensures your PV voltage is well above battery voltage, so the MPPT has plenty of wiggle room to control the battery charging.

 

[Sir squeegey]

Yeah, and just to clarify, with 2 panels, you would want to wire them in series, not parallel, you will have better results, as it ensures your PV voltage is well above battery voltage, so the MPPT has plenty of wiggle room to control the battery charging.

This is just a small 12v setup,wiring series would'nt that make it a 24v then?I only yave a single 12v battery

 

[DThames]

The MPPT charger will take the 24v (in this example) and reduce the voltage to the best charging voltage for the 12v battery. Actually it manages the current to the battery. With the panels in series, on a cloudy day, you have voltage high enough to do a little charging. If 12v panels are in parallel on a cloudy day, the voltage may be too low to charge, or only charge a tiny bit. The MPPT ability to use high input voltage is one of their features that make them better than the old PWM chargers.

 

[Sir squeegey]

Welcome to the forum.

Typical 12V 100W panels have a Voc around 22V and Vmp around 18. 2 in series would be well under the 75V limit of the 75/10; however,

200W/12V = 17A MAXIMUM - will typically be lower.

Thus a 75/10 (10A being the limit it can send to the battery, not the solar side) would not suffice.

A 75/15 would be the better choice.

Ok thank you, I will go with the 75/15.once I get all this fugured out I plan to build more with bigger and better.I watch alot of videos(Will Prowse)that man is a genious in the solar world,and eventually taking my home off grid partial if not all one day.enjoy the ?

 

[Hedges]

"100 ah sla batt"

A key parameter is maximum charge current. "SLA" (not to be confused with Symbionese Liberation Army, which was active while I was growing up) could be AGM or Gel. Gel in particular has a maximum allowed charge current.

Selecting (or programming, if that can be done) the battery charger would be a good way to set maximum charge current.