# MPPT Midnite Kid Charge Controller

Solar Expert Posts: 143 ✭✭
I am looking to buy this Charge Controller next year. I have been to another forum site and they said this can handle almost 600 watts of solar at 12v. The actual website states only 400 watts. Which is correct? And how many watts would you recommend?
1460 Watts Solar @24v. 675 AH Battery Bank using 12 6v Trojan T-105. 1 Midnite Classic 150. 1500 Watt 24v Samlex Pure Sine Inverter

• Solar Expert Posts: 6,006 ✭✭✭✭✭
Re: MPPT Midnite Kid Charge Controller

Well how do you want to look at it?

What it can handle is 30 amps of output, so working backwards for a 12 volt system, figure 12 volts x 30 amps = 360 watts input assuming 100% through put (I think it runs about 97% but we'll assume 100%) so if your battery was discharged 80% likely the charging voltage would be around 12volts. The charge controller monitors this charging voltage. As your battery becomes charged the voltage will increase at around 80% charged this is called the bulk charging. Once it reaches 80-85% charged the voltage tends to run away, at this point the charge controller maintains an absorption level, usually around 14.2-14.4 volts, this will vary depending on type of battery and manufacturer and even personal preference. So at 14.4 volts x 30 amps = 432watts. During this cycle/charging state the battery slowly absorbs less amps and likely you will want to set and end amps rate in your charge controller. After it reaches the end amps(or time frame) the charge controller will reduce the voltage to a float stage around 13.6 volts and try to maintain this voltage. it will allow more power to pass through the charge controller if it senses the voltage falling, like when loads are present.

So in this simple way of looking at it yes around 400 watts at 12 volts nominal.

...BUT, we haven't looked at the panels, solar panels rarely put out full rated capacity. Only on the odd clear fall or spring day when the sun is close to perpendicular to the array and the panels are cold. Most panels produce around 77% of their panel rating in watts. Many panels show a NOCT value (Normal Operating Cell Temperature) so if you make that figure 75% (including that 3% loss going through the charge controller) you have 400 x 1.30 = 530+ watts. So figure 600 watts as an economical over paneling, with a bit extra for those over cast days...

If you go to Midnite's forum you'll find the Kid can handle considerable over paneling, but 600 watts is a reasonable range to hope to reach around 400 watts of output on most days.

Clear as mud?
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 494 ✭✭✭
Re: MPPT Midnite Kid Charge Controller

I would run the Midnite Kid sizing tool and go with their recommendations.
http://www.midnitesolar.com/sizingTool_kid/index.php

You can overpanel the CC within reason as most of the time the panels won't be producing the maximum rating anyhow. However, the closer to maximum 30 amp output you run the unit the harder it is on the electronics. IIRC, Midnite recommends a max of 500 watts of PV at 12 volts.
Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
• Solar Expert Posts: 100 ✭✭
Re: MPPT Midnite Kid Charge Controller

I'm building a system that runs 390W of panel power (panel rating) and could go to 520 without issue with the Kid. Many people are. There is a good forum on Midnight's site about this.

In the real world, my 390W still be more like 300W. Your 600W will probably be more like 480W. Well within spec. Run the sizing tool.
• Solar Expert Posts: 492 ✭✭✭
Re: MPPT Midnite Kid Charge Controller

http://www.midnitesolar.com/sizingTool_kid/index.php

I have a few in service , Good !!
• Solar Expert Posts: 1,220 ✭✭✭✭
Re: MPPT Midnite Kid Charge Controller

The answer is it depends on your system voltage. As PW said at 12v 30A out is around 30*12/0.77 nominal derated input watts. FOr 24v system its twice that. For 48V system 4 times that. Its one of the reasons we prefer system voltages higher than 12v.
Zakarume wrote: »
I am looking to buy this Charge Controller next year. I have been to another forum site and they said this can handle almost 600 watts of solar at 12v. The actual website states only 400 watts. Which is correct? And how many watts would you recommend?
1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar