gee rhett,
you have been holding out on us! what other good stuff have you got tucked away over there?
as you know those Mitsubishi modules are what we are calling an 18 volt nominal panel ( a half step between nominal voltages?). lucky for us that we also have an mppt controller to go with it. now before we get too excited, a word^ about those bz 500's. i use the plural because that same controller came/comes in two different flavours and that may make a difference in our application here. first off these are all around great products for the price and i cut my teeth into mppt with these controllers, however they are not true open format mppt controllers like the mx, fx or apollo products and are "optimized" for their expected use. i have found that the 500 is good across limited ratio of mppt voltage conversion. example: on a 12 volt system we can run a 12 volt nominal module, an 18 volt or a 24 volt nominal array with good results. and any array with a volts open circuit (voc) above 50voc makes the bz 500 unpredictable. now thats the first flavour...the same looking model the bz500hv seems to like a voc between 30 and 80 voc and still has that same voltage conversion ability. ie across one full step in voltage. example: 24 volt system using 24 volt nominal, 36 volt and 48 volt nominal array.
if you take the four screws off the front cover you will find a paper label giving the firmware version and the 500 or 500hv designation. i could never get a series pair of 18 volt nominal modules (36 volt nominal for the string) to run with the 500. but had no trouble at all running them with the 500hv.
so i would have a look at the label and see what we have. if it's the 500hv i don't see a problem if it's the bz500 i would still try it and see if it might work. it would do no harm as they are both rated with a 100 voc limit. worse case would be to send it in for the upgrade service they offer. that company is very customer friendly, don't be surprised if you call and get frank himself on the line.
or via email:
Frank Lewon BZ Products bzp @ bzproducts.net "
see a full discussion of topic on this thread:
http://forums.altenergystore.com/Renewable-Energy/Technical/BZ-Products-MPPT500-step-down-voltage/index.php/topic,676.10.html"* Will the 2 different type controllers work with each other?"
they should play well together, folks do this all the time.
"* If I need to get another controller, should I get the MPPT?"
these oddball modules are most efficient with mppt but will work with standard pwm with lots of lost potential.
"* When I combine them,whatever they are, is it OK to let them wire together on the bars inside of the Trace DC 250 Disconnect, or can the two leads not 'touch' each other? If not, how then?"
yep, right to the same busbars.
rhett, about adding onto that bank. for the purposes of this public forum lets assume that the existing battery bank is less than a year old and is in good shape. what i would do is double my bank with the exact same batteries using identical cable, lugs and wire lengths. an exact copy of what you have. then run that second series string up to the dc250 power center and parallel them there at the dc buss.
best regards, dave
^ comments about the bz controllers are based on my experience only..your mileage may vary.