oldjohnt

Glenn, wow talk about any code requirements (NEC or Marine or RV) to provide Overcurrent Protection for the feeders "AT OR NEAR THE SOURCE" I think that pretty well has you covered...…...Id use those in a heartbeat provided they are the sufficiently rated for your current requirements ???? Also anytime you can reduce the number of cables and extra connections that's good. Now that you have "Overcurrent Protection" well covered for the feeders FROM the battery TO Load Inputs, you can install a Disconnect at loads such as Inverters or others for safety and convenience and/or as required (Unit may already have that covered??) If you want a pure disconnect only or say a breaker suitable for switching that's between you and what the manufacturers suggest (don't want to void any warranty) and if its needed ??? but I prefer and have at least a disconnect method especially for loads far removed from my batteries. As you already know having the Inverter close to the battery saves on line voltage drop and wasted heat energy concerns...…. Although Marine Grade is great and typically high quality and corrosion resistant and has excellent vibration resistance, using it in strictly RV applications may or may not be absolutely required BUT ITS SO GOOD AND SUCH HIGH QUALITY I've used it and prefer it. I often (right now as a matter of fact) am dry camped right on a beach so Marine grade is a good thing required or not. I still want to camp right next to you and plug into your energy source as you have enough to power an entire zip code lol John T

rb, If you're using a 12 VDC to 12 VDC Converter/Charger that can deliver 40 max charging amps OUTPUT into an auxiliary 12 Volt battery, due to heat loss inefficiency it may (subject to design) require something under 50 amps being drawn from your primary battery... So, a 50 Amp circuit breaker at your primary battery and another 50 amp at your auxiliary battery will "likely" work. If it trips at your primary battery (depends on converter draw current and time and time current curves of the breaker) you may have to use a bigger breaker, but that's still okay to protect 2 gauge wire. Based on a max current of 50 amps, that #2 copper welding cable has more then adequate ampacity and Id venture a guess wont yield enough line voltage drop to require any bigger wire be used. Hey I've seen far worse and more marginal wire size (like maybe 6 gauge use) so that #2 and 50 amps breakers at each battery WORKS FOR ME. When designing a branch circuit you FIRST compute the maximum continuous current SECOND size the wire to have a minimum ampacity of 125% of that, THIRD size the overcurrent protection device TO PROTECT THE WIRE not the device, that's another story. Its fun spending YOUR money lol John T

Dutch, I once had an older Onan Genset (before they became Cummins Onan) with a circuit board that went bad IT WAS FULLY EPOXY ENCASED and Onan charged something like $500 for them grrrrrrrrrrrrrr I called Dinosaur and they didn't make a replacement nor did they know of anyone who could disect and repair them. After looking and shopping for new or used I finally broke down and bought one BUT HEY IT FIXED THE PROBLEM what ya gonna do especially when on the road...………..I've owned RV's over 49 years and unless you buy say a Prevost or similar and pay a small fortune the darn things are built cheap n flimsy and no matter how old or new it seems were (or me at least) always having to repair them grrrrrrrrrrr. Theres no free lunch but I still wouldn't trade this lifestyle for anything. A buddy went to Florida last year rented a Condo and sat in it or at the beach 2 months, never talked to anyone else all the doors are closed of course, and got so bored he came home HEY IM NEVER BORED with buddys in the RV Parks and Antique Tractor Shows (where Im an exhibitor) and Bluegrass Festivals all winter wooooooo hooo Best wishes Dutch and others John T

Good discussion Lou, so much depends on the quality and features of his DC to DC Converter and its INPUT requirements (how low yet still deliver sufficient regulated charging voltage and current) and OUTPUT charge parameters. Of course, I'd still advise the use of a single bigger gauge wire then a string of SIX conductors all wired in parallel (that's just strange at best)..... I cant in good faith recommend that (even if it will "work") but hey its his RV his money and his choice certainly not ours. Fun sparky chatting with yall John T

Good afternoon Dutch, I would say if it keeps water off the sensitive components it could sure help, HOWEVER the answer depends on there remaining sufficient heat dissipation as coating would obviously affect that. Thermodynamics and heat transfer was NOT my cup o tea when studying electrical engineering so take this with a grain of salt lol Best wishes, John T Live beach camping in Port Aransas Texas

rb, while sure it can "work" its NOT how this retired electrical engineer would recommend. While it may not be exactly the same in your situation, when designing AC Power Distribution the use of parallel conductors (typically two, NOT six) was NOT allowed below certain wire gauge in case one conductor opened...…... Your use of large cable and quality low resistance connectors will greatly improve the charge balance when connecting multiple batteries in parallel CONGRATULATIONS.....I think we already discussed its best for balance if multiple batteries are the same type and design and size and even age?? Of course, when using a DC to DC Converter much of these concerns are not so applicable since it merely requires energy from Battery A and uses it to charge Battery B and thus compensates. John T

Vern, based on your observations and experience it looks like ANY brand of control board would fail under those (moisture) conditions !!!!!!!!!! Thanks for the technical info, it could help others. John T

Good plan Glenn, works for me and likely ???? complies with any applicable codes. John T

George, that may well qualify for having "Overcurrent Protection" "At or Near" the energy source. Its been too long and I would have to look up the specs concerning amperage and wire size and voltage etc. Again, the Magnum likely has its own built in limiting and overcurrent protection ON ITS OUTPUT and if so you're good FROM it TO the AC Distribution Panel John T

Vern, great info thanks for posting !!!!!!!!! DITTO on your advice to Try a Dinosaur Board, I've yet to ever have one fail yayyyyyyyyyyyy John T

Glenn, I would expect the AC Output of the Inverter has its own built in limiting protection so no additional DIY after market protection would then be required. Of course, as I explained below, your RV Distribution Panel indeed has "its own 50 Amp Main Breaker" to monitor the current that passes THROUGH and AFTER it, but that doesn't protect the WIRING FROM Inverter output TO the Panels 50 Amp Main, the Magnums output protection and limiting should take care of that. SEHC DITTO Indeed there are as I recall numerous applications where fuses are preferred over circuit breakers. DITTO Also catastrophic fuse protection can be required "at or near" the battery, I forget the distances and current and voltage etc. requirements. Yall be safe and take care now John T

Glenn built in breakers are all well and good for their intended purpose and I'm sure your Magnum is properly designed... HOWEVER FYI even if you are already aware for those who aren't, don't forget in order to provide "Overcurrent Protection" for the huge cables FROM the battery TO the Inverter those overcurrent protection devices (fuses or breakers) must be located at the source of energy the BATTERY not later somewhere downstream which would leave that portion of the cable (from battery to a breaker inside the Inverter) UNPROTECTED !!!!!!!!!!!!!!!! Yikes !!!!!!!!!!! That's a serious potential hazard with 2/0 Cables and a 21 KWH battery !!!! A breaker can only detect current that flows THROUGH IT not elsewhere like from a POS cable shorted to the RV frame BEFORE the Inveter !!!!! Of course there's no problem in overcurrent protection at BOTH locations (battery and Inverter) as well as On/Off switches NOTE in the area of Electrical Power Distribution there are applications where fuses are favored and others where circuit breakers may be NOTE for certain applications "Switch Rated" breakers are required that may not be necessary elsewhere John T Longgggggggg retired n rusty power distribution engineer and codes change so NO warranty...Consult the manufacturer and local practicing electrical engineers and electricians where fire and life safety is concerned ………...

Glenn, in order to provide "Overcurrent Protection" you need only one device and I often prefer fuses versus breakers. An On/Off switch is a separate issue and hey I have no problem with those. Sure, a proper circuit breaker could ??? serve as BOTH if that's YOUR choice and Magnum approves of such ??????????? NO you DO NOT need a Fuse plus a Breaker to provide "Overcurrent Protection" ...………….The time current curves would determine which opens first. NOTE "Overcurrent Protection" for huge cables FROM a battery TO an Inverter need located at the energy source IE the battery, not far downstream leaving cable unprotected !!!!!!!!!!! John T

Thanks for the update rb, Yeppers I was mostly talking about the basic concepts regarding parallel connection of two batteries (with or without any fancy multi battery isolators) and the necessity of large cables and quality low resistance connections. Indeed any "smart" technology in your alternator or DC to DC Converter makes for a better quality charge as well as charge balance...….. You're well on top of this, good luck I rely on my Smart 3 stage solar charge controller to charge my three AGM house batteries but do have an "emergency" jump cable relay in place so if needed my engine battery and its (non smart) alternator can provide at least some degree of charging (albeit not perfect or balanced or politically correct lol) back to my house battery bank. I can also use it if my engine battery happened to run down which has happened and I was glad I had the emergency jump feature built in yayyyyyyyyyy John T Boondocked and live from Padre Island Texas but headed to south central Florida for most of the winter

rb, as you already know its best when connecting multiple batteries (to achieve better load and charge balance) they be the same type and design and even age but sure it can still 'work" even if not. That being said, especially if there are long cable runs joining two batteries, the cables should be as large as possible and likewise any connections be quality and low resistance....If one battery is near the alternator but another farther away you can realize (line voltage drop and resistance) how the one may not get the same charge quality and completeness as the other. I'm sure you're also aware they make both solid state as well as mechanical isolation relays intended for dual battery systems which allow the main battery to be charged as well as an auxiliary battery. Typically an automotive alternator and its charge control regulation is not as well defined and precise as say an RV type of Smart 3 or 4 stage charger and especially a smart charger which has provision for FLA or AGM or Lithium HOWEVER sure it will work its done often and the world goes on lol.. Quality cables and connections and similar batteries can just make it work better WELL DUH John T

Typically when an RV furnace (NOT all maybe NOT yours??) t stat calls for heat the blower motor will start, the sail switch makes up, the high temp limit safety switch must be properly as normal closed, and if all that's in place and working after a delay the circuit board will receive voltage, the gas valve opens and the HV ignitor tip (via HV coil/transformer usually on circuit board) starts sparking to ignite the gas. If there's no flame the flame sense safety circuit closes the gas valve. Some will try 3 times to light before they lock out...…... I say all this so you will realize YOUR PROBLEM MAY BE SOMETHING OTHER THEN THE CIRCUIT BOARD but sure it may well be I cant know from here...…. In 49 years of RV ownership and as a past used dealer I often saw faulty ignitor tips (incorrect gap or hairline crack or carbon trace) was the cause of no ignition as well as LOW VOLTAGE or loose or resistive wires, connections or corrosion or poor grounds. Insure there's good voltage to the furnace and control board and check all wiring and connections and grounds GET A MANUAL AND work through its troubleshooting tips but low voltage or poor or loose or corroded connections or bad grounds or faulty ignitor tips could be the problem. On appliances that used a flat ribbon cable that attached to the circuit boards I have seen where that connection just needs cleaned (caused low voltage to the board) and on my own furnace recently that failed to light like yours a simple ignitor tip gap adjustment cured the problem. Ive never had a Dinosaur replacement board go bad in case it turns out that's what you need...... John T Live boondocked in North Padre Island Texas

Good Point Dave, if he goes with a 48 to 12 Converter and no 12 volt batteries whatsoever, he needs a good quality and a sufficient rated, especially surge rating, DC to DC Converter. I prefer as simple as possible and as few as possible devices and appliances and black boxes, that's one reason Id opt for a SINGLE 120/240 Volt Inverter with enough power to run allllllllllll his 120 and 240 loads and no extra 12 volt batteries IF FEASIBLE THAT IS...…….?????? But of course, your method of having a 12 volt battery certainly has some advantages..... Best wishes Dave, nice sparky chatting with you John T

FOR THE RECORD, a typical RV has an internal often referred to as a "Converter/Charger" or just "Charger" which Converts 120 VAC shore power down to 13/14 VDC to Charge the 12 Volt Batteries. HOWEVER what Glenn needs and is talking about is a "DC to DC Converter" so he can uses his 48 Volt Battery bank (Converted to 12 Volt) to power his RV's 12 Volt lights and vent fans and water pumps and furnace and slide motors etc. etc. His 21 KWH 48 VDC Lithium Battery bank can power SEVERAL of our RV's lol much more then a typical say 100 Amp Hour to even 500 to 1000 Amp Hour 12 Volt Battery banks many use. John T

Glenn, As long as you have a quality high voltage (say 40 to 60 or so VDC) to 12 VDC Converter with sufficient power to operate all your typical 12 Volt Appliances (Vent fans, furnace, water pumps, slide outs, lights etc) I agree you have no need for additional 12 volt batteries.... BUT this is a choice and preference, sure there are other suitable methods should one so choose for whatever reasons such as the method posted above ... Hey you already have plenty of electricals lol John T

Good choice and I agree WE PRETTY MUCH BEAT THIS ONE TO DEATH LOL It was fun helping you design such a huge system and again CONGRATULATIONS. John T

EXACTLY what I've told him more then once ……………. He can EITHER use two 120 Volt Inverters that are correctly phased and synced to achieve 240 (When L1 is + 120, L2 is - 120) OR One true 120/240 Volt Inverter and be done with it. If a SINGLE 120/240 unit is available with sufficient power rating to suit his needs ???? that's a fairly simple operation. John T

Great, thanks for the updated info Glenn. Sooooooo since BOTH mini splits are 2800 Watts Max AND SUBJECT TO YOUR OTHER ENERGY DEMANDS (Need that energy audit) I would still think a minimum Inverter size "might" be around 5000 or so Watts. If your energy audit confirms 5000 is plenty ?????? (I cant say from here) it may be easier and cheaper to go with a SINGLE UNIT 5KW or larger if needed that offers 120 as well as 240 volts and no additional transformer is required......…. You're absolutely correct, voltage drop versus SOC is less on Lithium then lead acid and you can discharge Lithium deeper then Lead acid. However my own personal preference would be still not to discharge over 80% before recharging. John t

Glenn, if indeed ???? (not saying don't know from here) you need to power TWO mini splits at same time which could use 2800 watts each, you obviously need AT LEAST 6000 watts of Inversion capacity which doesn't leave much wiggle room for other loads running at the same time. Iffffffffff indeed ??? that's the case you would need AT LEAST (A) A couple 3000 Watt 120 Volt Inverters (Synced and phased so L1 & L2 are 180 opposite and 240 is available) orrrrrrrr (B) One single 6000 watt 120 Volt Inverter coupled with a 120/240 transformer orrrrrrrrrrr (C) One single 6000 Watt 120/240 Volt Inverter to power BOTH 120 and 240 loads. I still don't know the energy storage capacity of your battery bank which needs to be known to compute how long you might power up two mini splits for X time. Regardless if your batteries are LiFePo4os or Lead Acid or AGM they do have an energy storage capacity rating and remember Energy is Volts X Amps (or Watts) X Time such as Watt Hours or Amp Hours etc NOT just Watts. Watts represents instantaneous Power while Watts X Time represents Energy such as Watt Hours the Utility charges you for. NOTE DIVERSITY is another factor that can come into play when designing power distribution and that could (if applicable) possibly lower the above rough approximations. You're getting there John T

I LOVE LED's in my RV, have replaced all the old incandescent and wouldn't go back !!!! If you shop on Amazon or E Bay or any of the other thousands of sources you can find them in the Lumen and Kelvin temperature rating and the price and quality of your choice SO INEXPENSIVE. As an electrical engineer I like the fact they use sooooooooooo much less energy, more light per watt, and produce so much less heat. HOWEVER I believe each should use what they please and what works best for them be it incandescent or halogen or sodium or LED …. John T

Hey Glenn, I proudly consider myself to be a Geek but this is too complicated and unnecessary even for me lol. When one of my buddys and I are fabricating a project in our RV park and questioning just how good it needs to be, his response is "Its good enough for the women we run with" Nuff said, John T