step down converter

[opticalmike]

I am looking to upgrade my RV solar setup. Currently I have 4- 85 watt 12 volt panels, a midnite combiner box with 4 DC breakers and a 30 amp CC(not mppt). 4 T-105's. I have a 3000 watt pure sine inverter(overkill but it was cheap) to plug the shore power cord into. I have installed a battery disconnect that I use as a manual transfer switch, thats installed on the positive lead coming from the trailer converter.This prevents the trailer converter from trying to charge the batteries
I would like to add a kid and whiz bang jr as well as another big panel....a 235 watt 24 volt Hanwha. So to reconfigure the 4- 85 watt panels to 24 volts seems easy, but then will I need a step down converter to
drop down to 12 volts, or can the kid do this too?
Thanks in advance,
opticalmike

[chris]

well.....the kid will take the extra volts and convert them to amps for a 12 volt system, but in my opinion those panels are not really compatible.......you'd be better off ditching the 85 watters and just running 2 of the 235's

[opticalmike]

I have a rubber roof with mounting brackets for the 4 panels...trying not to make swiss cheese of it. just trying to get more watts without covering the entire roof of the fifth wheel with smaller wattage panels. I wonder what the biggest panel I could add that might be more compatable??

[tecnodave]

Mike,

The Hanwa panels are 60 cell and your older panels are 36 cell, the voltages are going to be too different to work well togather. If you can find 72 cell panels this might work for your situation. Chech the voltage at maximum power ( VMP ) ratings of each panel, if you are real close it will work well. I'm using 36 cell 55 watt Siemens panels in half of my array and 72 cell Suntech 280 watt in other half. I got the voltage within .5 volt so everything works well togather. I think your smaller panels are 18.7 v@max pover X2 is 37.4 and the Hanwa is 29-30 volts, no match.


Might I suggest that you slightly modify your shore power converter to save a bit of power, just add a toggle switch to turn off the 120 vac to 12 vdc converter , inside at the circuit breakers there is a small black wire about 18 Guage that feeds the transformer in the bottom half , switch that lead to turn off converter part of power panel , and you will save a lot of unnecessary power as your batteries will be charged by solar and the converter is not very efficient, maybe idle ing with no load at 100 watts power. There is a relay in the bottom of converter that runs all the 12 volt systems from this converter when you connect to shore power. If you don't disable this then power will go from batteries to inverter at 12 volts , get converted to 120 volts, then to converter at 120 volts ,converted back down to 12 volts then to trailer loads at 12 volts . Double converting = huge loss of power.

Or maybe easier, don't plug shore power cord into inverter, wire a separate inverter only circuit.

I hope I have explained this well enough. I have a Tioga Motorhome converted to a mobile cabin and have been through this one.

td

[chris]

Or maybe easier, don't plug shore power cord into inverter, wire a separate inverter only circuit.

I hope I have explained this well enough. I have a Tioga Motorhome converted to a mobile cabin and have been through this one.

td

  I found the easiest solution to this (31ft Keystone travel trailer/cabin) I added another breaker to the panel to shut off the converter....this way I could still plug the shore power into the inverter to light up all existing plugs.

[tecnodave]

Chris,

Yes that will work as long as you shut off the power transfer relay and the DC converter as well.

Mine has only 3 oddball breakers (G-E Pushmatic) and I would lose my counter top circuit as well so I hacked it.

td

[vtmaps]

I would like to add a kid and whiz bang jr as well as another big panel....a 235 watt 24 volt Hanwha. So to reconfigure the 4- 85 watt panels to 24 volts seems easy, but then will I need a step down converter to
drop down to 12 volts, or can the kid do this too?

Welcome to the forum,

You can keep your old panels and controllers as they are, and add a kid and new panel.  No problem having multiple controllers all charging the same battery.

Technodave's suggestions are smart... when you are inverting, don't let any of your 120 volt power get to the converter.

--vtMaps

[tecnodave]

Opticalmike,

<quote>
I wonder what the biggest panel I could add that might be more compatable??


I have found Epolly brand panels are 72 cell that work well with legacy 36 cell panels. They have a 26" wide module that is a way easier fit on a motorhome as the standard grid tie panels are wider at 34-36 inches and much harder to fit on coach. These are 190 watt, 72 cell, 26" X 54" or so skinny enough you can place alongside of roof vents etc.

Found at NAWS website, they also carry a Chinese clone with the same specs.

Best  $/watt value I've found in a non standard grid tie type of module

td

[opticalmike]

Thank you very much for the wealth of knowledge!
I would love to add the kid and one of those 26" Epolly panels.

what if......
I were to wire in a plug from my 3KW inverter to a ground fault receptacle behind my tv stereo area. Make up a suicide plug male both ends.
plug goes from my ground fault receptacle to the adjacent trailer receptacle thereby energizing the whole trailer. NEVER plug shore power in again...while suicide plug is hooked up.
I do have a breaker on my panel that says generator. I have no generator. Perhaps I could tie into that...
thanks in advance
opticalmike

[TomW]

what if......
I were to wire in a plug from my 3KW inverter to a ground fault receptacle behind my tv stereo area. Make up a suicide plug male both ends.
plug goes from my ground fault receptacle to the adjacent trailer receptacle thereby energizing the whole trailer. NEVER plug shore power in again...while suicide plug is hooked up.
I do have a breaker on my panel that says generator. I have no generator. Perhaps I could tie into that...
thanks in advance
opticalmike

Mike;

It would be best to install a transfer switch where the wiring enters the breaker panel. For years I used common plugs and outlets to switch circuits from grid to inverters. 2 outlets, one for inverter one for grid. A plug on the feed to the circuit. Switch where its plugged in to use the different source. Still funky compared to the transfer switch but better than the suicide plug idea. Pretty fool proof as you cannot be plugged in to both at same time unlike the suicide plug.

Just thinking out loud.

Tom

[tecnodave]

Mike,

As a practicing electrician........ Do not do a male plug to male plug........DEADLY UNSAFE!

The wiring in most campers, motor homes etc is 14 Guage wire rated at 15 amps at 120 volts , that is 1800 watts. You would not have any protection from over current and the possibility of fire as a result.

Your suggestion to use the generator breaker is excellent. It should have a transfer switch built into the breaker panel as in no condition you would want shore power and generator connected togather.
In any case get some kind of over current protection in there.

If you do connect to gen input of power control panel you will still want to shut off the converter part of the panel.  This is not difficult as all of the external circuits are solid wire, only the converter wire is stranded. Put this one on a separate breaker.  Most of these panels use Bryant breakers same as a household panel. If you have single space breakers you can subsistute tandem breakers in their place to gain a circuit. See what brand breaker is there and buy same brand twin breaker. Other brands will fit but will void your UL or ETL listings for that panel and may be an issue with insurance if a disaster happens.

td

[tecnodave]

Mike and TomW,

Motorhome circuit breaker panels are vastly different than home panels,

They are multifunction as follows:

1). AC power distribution panel ...main breaker and branch breakers

2). Sometimes includes transfer switch for shore power/ Generator

3) DC power distribution panel with fuses for DC in from batt and branch circuits

4) AC to DC converter to supply 12 volts to trailer loads when AC is present

5) house lighting battery charger....part of converter but has separate voltage control

6) power transfer relay.....this relay has a 120 volt AC coil but 12 volt contacts.....no AC output connected to battery input.....AC present ...DC output connected to converter box


To do solar properly you need to shut off functions 4 5 & 6......this is simple as the same wire that feeds the converter in the bottom half feeds AC to converter and power transfer relay.

All the external AC circuits are Romex type wire ( white outer jacket over black , white and bare solid wires.  There is only one stranded wire in the AC compartment that feeds the AC - DC converter normally 16 or 18 g.a.

If you put power into the AC panel from either direction (shore power plug or back feeding ) you will turn on the converter and power transfer relay same if you add a transfer switch before the converter box.

If not sure about minor wiring changes post exact model converter box, mine is B&W 6300 as are many other motor homes and I will try to walk you through this easy modification.

Due to lack of availability of G-E Pushmatics, I drilled a half inch hole in panel and added a SPST toggle switch to turn off converter portion of power panel.

By the way, I have found that IOTA brand battery floater/charger to be way more efficient for RV use so when I get a damaged B&W converter I generally wire the Iota in place of the original converter portion of power control panel. $$$. Good Iota. 45amp. =$135.  or so. Original B$W box 45a.  $$850.

Iota is way quieter <edited>and more efficient than original transformer design.

td

[tecnodave]

Most motor homes in Class C do not have shore power transfer switches, they accomplish this rather easily, the generator output is directly wired to a outlet box in the shore power cord storage area. To use generator, plug shore power cord into generator outlet connector....same connector as shore power cord......manual power transfer plug and socket. walla...No way to plug into shore power and generator at same time.......wire output of inverter to one of these RV connectors and plug in shore power cord to inverter output socket. These are special connector for RV use only and can be a bit tough to find. Home Cheepo used to carry them and OSH does but any RV dealer has them

I stock them and will post correct numbers for connectors soon.

td

[vtmaps]

Iota is way quieter and power factor corrected switch mode so much more efficient.

The Iota battery chargers are NOT power factor corrected.  They are rugged and reliable and cheap.  They work great with grid power, but have caused a lot of angst for folks who try to use them with small generators.  Two problems come up... very high inrush current and low power factor.

read: http://forum.solar-electric.com/showthread.php?10123

--vtMaps

[tecnodave]

vtMaps,

Thanks for that info, my bad, I thought that they were power factor corrected. I will edit that post as I do not want to give out bad info.

My generators have huge surge capability as I use wound rotor motors in a lot of my work and the Honda's and such do not survive this duty. I'm using Onan's as they have 4 times the copper in the windings as compared to generators of same power that have built in fuel tanks and wheels.

td