RV 24v Charging

[bloke]

Hi
Just bought an RV with a 30amp The Kid controller/charger.
I'm going to have 2 x 140ah AGM Deep cycle batteries in series for the 24volt. The RV is a 24 volt system so I can charge the batteries with the alternator via an isolator while driving. Then convert the 24 volt to 12 volt to run a fridge etc.
The recommendation in the MidNite Solar manual is 2x 250watt panels in series with each having a VOC
of around 37volts. I'm struggling to find a 250w panel with VOC 37volts. How critical is this voltage?
Is it ok to use 250w panels with a VOC of 45 volts each? From what I've read the limit for the VOC is 150 volts. What affect does it have on the system as the VOC is increased?
Cheers

[ClassicCrazy]

There is a string calculator on the Midnite website that you can put in different PV panels .
But basically any PV voltage under the limit of 150v VOC is fine - except that you need to calculate in how cold the PV temp will be. The colder the PV get the higher the VOC will go. The string calculator tells you all that.
 https://www.midnitesolar.com/sizingTool_kid/index.php
You need to have a PV voltage a certain amount above what your battery voltage is for the Mppt of the Kid charge controller to work.
Ideally you have the PV voltage at or a bit above the needed mppt charge voltage because the closer it is to the battery voltage, the more efficient the Kid will be .
Anyway - your two 25 volt should be fine even if you put them in series. They might be okay also if you put them in parallel too.
The string calculator will give you the analysis.
Larry

[bloke]

Thanks for that information. The sizing tool is a great help. I'm just a bit unsure how many amp/hrs I could have on board as that is not input into the sizing tool.
Cheers

[ClassicCrazy]

Thanks for that information. The sizing tool is a great help. I'm just a bit unsure how many amp/hrs I could have on board as that is not input into the sizing tool.
Cheers

Amp hours of batteries ?
If you are talking about battery capacity you can have as many as you want, though best to have enough solar to be able to charge up what you use  the next day.
Larry

[bloke]

Thanks Larry
Yes battery amp/hours is what I mean.
I'm thinking of trying 2x12volt Lithium 150amp/hr each with 2 panels 415 watts each.
Batteries in series for 24 volt and the 2 panels in series. Midnight solar is the 30 amp version.
Am I heading in the right direction??
Cheers
Ian

[ClassicCrazy]

If you want to go 24v I would get a 24v battery instead of two 12v .
Get the kind that have monitoring available either by bms app, pc software, or display on the front.
Check into SOK, Signature Solar, Jakiper and compare . Lithium prices are pretty low now so good time to shop for them.
Do you already have the Midnite Kid ? That is the 30 amp . If you don't have it I would check into Midnite DIY line or a Classic since that gives you more room to grow your system and better remote monitoring than the Kid has.
Larry