Midnite Solar Classic 200 set up help..

bryhan67 said:

Hello all.. Trying to set up my classic 200. Little confused on battery amp hours. I have 10 T-105's what hour rate should I use? 20 hour is 225ah's I am running 12v system. 10 x 225 is 2,250ah @ 6volt. So would I use 1125 for my ah's? The manual was not clear on different voltage. 

Welcome to the forum,

Your batteries are configured as two in series (a 12 volt string), and you have 5 strings in parallel.

Each string is 225 ah at 12 volts.  The 5 strings in parallel have a 1125 ah capacity.

Your system (what little I know about it) raises a couple of red flags:

First: 5 strings of batteries is very poor design for a system that is going to be cycled frequently.  When charging them, the current will not divide equally among the batteries.  As the system becomes unbalanced, you will ultimately reach the point where some batteries are actually discharging into other batteries.  You will need to use bus bars in a battery combiner box to wire the batteries.  Also, for safety reasons, each string needs a fuse.  The fuses will add complexity, resistance, and more potential points of failure to the system.

Second: You have a Classic 200 with a 12 volt system.  This raises some concern about running the classic cool and efficiently.  When the input voltage to the Classic is much higher than the battery voltage, the Classic is less efficient and has lower rated capacity. 

Since you have a Classic 200 (rather than a Classic 150), I presume it is because you are running a high PV string voltage to the Classic.   Stepping that high voltage down to 12 volts is very inefficient.  The Classic 200 should usually be used with 48 volt systems (or even 72 volt systems).  

The lower rated capacity of the Classic (at higher input voltage) is to protect it from overheating.  How many watts of PV panels do you have, and what is the Vmp of the combined PV output?  Hopefully you are nowhere near the Classic's capacity limit because it is not a good idea to run them for hours on end when they are on the verge of melting.

--vtMaps

bryhan67 said:

 I understand everything you said except about my battery bank. I never recall seeing a battery bank with that needed a buss bar with 5 breakers.   Can you elaborate more about the batteries.

try reading this short thread:
http://forum.solar-electric.com/discussion/13179/series-rule-of-thumb

and this site:
http://www.smartgauge.co.uk/batt_con.html

--vtMaps

bryhan67 said:

Do you have a diagram how you recomend to set them up for 12v?

Use method 3 on this smartgauge page.  It will require the use of bus bars.  The smartgauge site does not show the fuses that are required for safety.  When charging the battery bank you hope that the current will divide equally among the 5 batteries.  At some point you may have a situation where all the current is going to just 1 or 2 batteries.  That can lead to danger... thermal runaway.  That is why you should have a fuse for each battery.

It would also be a good idea to invest in a DC clamp amp meter to monitor the discrepancy among the batteries.

--vtMaps

bryhan67 said:

I have 6v batteries wiring 12v do you have a diagram for that? Thanks

Here is a diagram with 4 strings of batteries connected in parallel with bus bars.  Each of the 4 strings is two 6 volt batteries in series. 

This diagram does not show the fuses, but each string should have a fuse.

--vtMaps

Btw the reason for the fusing is: if you get a chunk of plate fall off a cell, shorting the cell or battery out, if you have parallel strings the shorted string will dump the contents of the good strings into the dead short.

The reason for the busbars (or otherwise exactly equal cable lengths) is that batteries have low internal resistance and the higher resistance in your diagram of the cables to the batteries furthest from the main cables will tend to make current sharing uneven.

Indeed these are the forum breakers of choice:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1/mnepv.html
or
http://www.solar-electric.com/installation-parts-and-equipment/midnite/cipr1/stfubr1/pamodccibr.html

For something to put them in:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/misobigbabox.html
or
http://www.solar-electric.com/installation-parts-and-equipment/midnite/elenanddcdi/midcdipoce.html

Delivered to your door anywhere in the world. Aint it great?

There is a lot of expense involved in trying to use 5 batteries in parallel... fuses. bus bars, etc. And for what?  You will have an unstable, short-lived battery bank even if you have perfect wiring. 

You can put 8 of those T-105's in series to make a 48 volt system.... how much will it cost to make the switch to 48 volts?  And how much of that number will you spend trying to avoid 48 volts? (bus bars, fuses, conduit, electrical boxes, battery cables, etc).

Sizing of the fuses is tricky... If they are too large, you don't have adequate protection.  If they are too small, you may run into cascading failure. 

Cascading failure:  Suppose that the peak current you will ever draw from the battery bank is 500 amps.  You put a 150 amp fuse in each of the 5 battery strings.  If one battery has a poor or corroded connection or has high resistance, you would be drawing the 500 amps from just 4 strings... 125 amps per string in theory.

In practice, the batteries will not be perfectly balanced... as soon as one battery exceeds 150 amps, its fuse will blow and the 500 amps will be drawn from the remaining 3 strings, causing their fuses to blow in a cascade of dollars spent.

I don't know what advice to give regarding fuse size for individual battery strings... I would never design a system in which the question needs to be asked or answered.

--vtMaps