Ron's RV Power Questions

RonShaw
RonShaw Registered Users Posts: 7
[moderator: Moved the following posts to its own thread--Was here before: 5th Wheel RV Solar/Battery/Inverter Upgrade -Bill B.]

Hoping to jump in for some advice. I'm in the process of cleaning up the wiring in my camper - very similar issues & questions.

I have a 1500w inverter, solar and 2 6volt batteries and a 45w converter already installed - all works well except the number of wires going direct to the battery. Now I am installing a Trimetric monitor with 500 amp shunt. The 500 shunt is supposed to be installed on the negative side of the battery. I want to clean up the wiring while I install the Trimetric.

Can I connect all the positive & negative leads/inputs - inverter, solar, 12 lights etc, converter to pos & neg bus bars, then the positive goes to the batteries and the negative goes to the shunt, then shunt to battery?

I'm trying to get my head around the way current flows to and from the battery and am getting confused.

Wiring size is the next question. The inverter already has 2 gauge and battery interconnect is 2 gauge. Converter is 4 gauge, solar is 8 gauge.
Several other 10 gauge etc.

If I connect the 4 gauge, 2 gauge and others to bus bars, should the wire that goes to the battery be significantly larger than 2?

Final question, the solar disconnect between the panels and the solar controller - does it have to disconnect both negative and positive wires. If so, what sort of double pole switch would be best. 350w solar power.

Thanks

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: 5th Wheel RV Solar/Battery/Inverter Upgrade
    RonShaw wrote: »
    Can I connect all the positive & negative leads/inputs - inverter, solar, 12 lights etc, converter to pos & neg bus bars, then the positive goes to the batteries and the negative goes to the shunt, then shunt to battery?
    That is correct. I presume that you want to also negative ground the battery bank too... That should go to the same side of the shunt as the rest of the return wires. You do not want any other electrical connections between the shunt and the negative post(s) of the batteries... Otherwise, the shunt will not measure the current flow for those devices.
    I'm trying to get my head around the way current flows to and from the battery and am getting confused.
    The shunt could go in either the positive lead to the battery bank or to the negative lead. I believe they use the negative lead because if there are any shorts to the shunt to ground (or the sense leads to the battery monitor to ground) there is no current flow/short circuit (everything is zero volts) so no fusing is required for shunt connections.
    Wiring size is the next question. The inverter already has 2 gauge and battery interconnect is 2 gauge. Converter is 4 gauge, solar is 8 gauge.
    Several other 10 gauge etc.

    If I connect the 4 gauge, 2 gauge and others to bus bars, should the wire that goes to the battery be significantly larger than 2?
    Any wire/cable that leaves the + Bus connection should have a fuse protecting the wire... I.e., a 14 gauge wire leaving the bus should have a 15-20 amp breaker.

    Fuses/breakers are only there to protect the associated wiring from excess current flow causing the wire to overheat and start a fire (it is not there to protect a pump, fan, lights, etc.--just the wiring to them).

    A 2 gauge wire can handle around 180 amps or so (there are lots of derating factors--type of insulation, in conduit, in bundles, etc.)... So you might use a 150 amp fuse or 175 amp breaker (mounted near the bus bar) to protect the wiring.

    Frequently for solar PV systems, we use much larger cabling because of problems with voltage drop. A 1,200 watt inverter may need a circuit rated for:
    • 1,200 watts * 1/10.5 volts * 1/0.85 efficiency * 1.25 NEC derating factor = 168 amp rated circuit/fuse.
    So, for that inverter, the minimum circuit would be 175-200 amps. But perhaps you want 1/0 cable to keep voltage drop lower--So, the fuse/breaker may be smaller than what would be used for the 1/0 cable. (check installation manual, they usually tell you the maximum input fuse/breaker you should use).

    Now, if you have 175 amps circuit going to the inverter and you have 50 amps from one charger and 40 amps from another charger. The total flow to/from the battery is never going to be 175+50+40=265amps because the 50+40 amps is subtracting from the 175 amps, not adding (one load and two charging sources).

    The wire back to the battery should be rated at what you expect the maximum supported current should be... For a standard lead acid battery bank, the max continuous surge current should be ~C/2.5 (20 Hour battery rating in Amp*Hours divided by 2.5). Say you have a pair of 100 AH batteries:
    • 2*100 AH / 2.5 = 80 amps recommended max surge from bank
    • 80 amps * 1.25 NEC rating = 100 Amp Battery Wiring Rating
    That is probably the minimum I would plan for... If you want to try and run a 1,200 watt inverter at full load, you are looking at needing a 168 amp (or 175/200 amp) rated circuit.

    So the wiring to the battery should have a 175 amp breaker and ~2 AWG wiring to support the 1,200 watt maximum output of the inverter (at low battery voltage) in the above example.

    Also, remember you may have the 1,200 watt inverter and some other loads too... Your battery probably may not be able to run all of them at the same time--So installation a too large set of wiring/breakers may be just a waste of money (unless you are planning on enlarging the bank later).

    -Bill

    PS: Forgot this part:
    Final question, the solar disconnect between the panels and the solar controller - does it have to disconnect both negative and positive wires. If so, what sort of double pole switch would be best. 350w solar power.
    Normally, for a negative ground system, you only need to switch/fuse/breaker the positive lead... Leave the negative/ground/return wires all connected with no fuse or switches.

    If you choose to switch/breaker the PV Array, switches are rated for AC/DC and Volts/Amps (the AC ratings typically larger than the DC equivalent for the same switch). So, what Voc/Imp rating will your array be?

    -BB
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: 5th Wheel RV Solar/Battery/Inverter Upgrade

    There is no reason you can run all the "home runs" to a pair of buss bars, and then shunt the negative near the battery. I would fuse the first positive at the battery, using a Bluesea terminal fuse of appropriate size for the total current expected along with the wire size. Your 1500 watt inverter might draw over 125 amps at 12 vdc so you will need to fuse that final cable for that load (as well as use a big enough wire).

    http://bluesea.com/category/5/21/productline/overview/378

    Then I would fuse each branch load at the buss bar, so inverter would get a big wire and fuse, the smaller 12 vdc loads would get separate fuses even if they feed a sub panel. You must protect the wire from the buss bar to sub fuse panel.

    Whether or not you need # 4 wire or something bigger is a matter of sizing the wire for the total load, once again, your inverter is going to be the biggest load.

    Bottom line, fuse every wire for the ampacity of that wire, as the loads get smaller, use smaller wires and smaller fuses.

    Hope this helps.

    Tony

    PS Damn your fast Bill!

    Just one more note,, you are not going to be wanting to run anywhere near 1500 watts from your inverter at 12 vdc! You battery and inverter is going to go to low voltage disconnect right smack away if you load them with ~ 1500 watts. The batteries are just not big enough for that kind of load. In our off grid house, with three times as many batteries, we run a 300 watt inverter and never have more than ~ 150 watts at a time for loads, and never more than ~ 200.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 5th Wheel RV Solar/Battery/Inverter Upgrade

    "PS Damn your fast Bill!"

    he is isn't he? he does that to me not only for post replies, but also when we're zapping a spammer at the same time.
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: 5th Wheel RV Solar/Battery/Inverter Upgrade

    Tony & Bill, thanks so much. Great info and explanations & a couple more questions.

    I have 2 - 6 volt - 232 a/h batteries. The 1500 w inverter was a deal otherewise I would have gone smaller, but not planning on using anywhere near that. Likely 100-500 max and only a few minutes at a time.

    The PV panels total 315watts - 18 amps.

    The Inverter came together with a fuse - I believe it was a 150 or 200 amp, already installed. I've seen the Blue Sea fuses for the battery at West Marine and was considering them. All the branch lines have fuses or circuit breakers already.

    Any recommendations or sources for a type of disconnect switch for the PV Array?

    Would you recommend soldering the crimp on connections, or is that overkill? I used to have a boat and due to corrosion getting into the wiring, soldered most connections after crimping.

    One theoretical question - I'm struggling with this one.
    With the truck's alternator or the RV converter when connected into 120volt/generator, putting a charge into the batteries while driving or plugged in, and the solar panels (which have a controller) also charging, do they work together well - are the amps going in cumulative or would the controller be fooled to think the batteries have more power because of the charging from the alternator &/or PV?

    Thanks again - appreciate the help.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: 5th Wheel RV Solar/Battery/Inverter Upgrade

    Ron,

    I moved to your own threads so we can better follow the Q&A. -Bill
    RonShaw wrote: »
    I have 2 - 6 volt - 232 a/h batteries. The 1500 w inverter was a deal otherewise I would have gone smaller, but not planning on using anywhere near that. Likely 100-500 max and only a few minutes at a time.
    Check the Zero load draw on the inverter--Larger inverters usually have higher losses when powering small loads...

    Also, if you have an MSW (Modified Square Wave) type inverter--you might want to read about TSW (True Sine Wave) Inverters... They do draw more power than MSW at low power--But some 10-20% of the loads driven by an MSW inverter (wall transformers, some electronics, motors, etc.) can draw upwards of 20% more power when on MSW and overheat.

    All About Inverters
    Choosing an inverter for water pumping

    MSW inverters can be rediculously inexpensive compared to TSW--But if you need reliability out in the middle of nowhere--I would consider getting a small TSW inverter (keep the big guy when you need lots of power).

    For 12 volt battery systems--The MorningStar TSW 300 watt (600 watt surge) inverter is hard to beat. It also has a "search mode" and a DC inhibit connection which puts the inverter into a very low power mode except when >6 watts of load is detected or your turn on a small DC remote switch.
    The Inverter came together with a fuse - I believe it was a 150 or 200 amp, already installed. I've seen the Blue Sea fuses for the battery at West Marine and was considering them. All the branch lines have fuses or circuit breakers already.
    You might want to look at a 175 amp DC Circuit Breaker for the inverter (if you do not already have a DC switch) to allow you to only turn the inverter on when you need it.

    Mini - DC Disconnect Power Center with 175 Amp Breaker
    Marine Rated 60-150 Amp DC Breakers

    DC breakers for higher currents are not cheap... (DC is more difficult to "break" than AC with similar voltage and currents).

    Otherwise, you can use a switch and fuse for the inverter.

    Oversizing the inverter can be very costly if you do not need anywhere near that amount of power.
    The PV panels total 315watts - 18 amps.

    Any recommendations or sources for a type of disconnect switch for the PV Array?
    In a previous lifetime, I would by DC breakers and switches from aircraft wrecking yards. But any switch rated for Voc of your panels (30-150 VDC and 20+ Amps) would be fine.
    Would you recommend soldering the crimp on connections, or is that overkill? I used to have a boat and due to corrosion getting into the wiring, soldered most connections after crimping.
    About the middle of this thread talks a bit about crimp vs solder and the tooling required.

    And a long discussion about the pros and cons of crimp vs solder.

    Short answer--People still like to use solder (after the wires have been mechanically secured) but most modern equipment uses purely crimp.

    My personal opinion is that crimp is the more reliable connection... If you have corrosion problems, need to seal the joint (tape, sealant, etc.). Solder creates its own problems with making stranded wire solid and creating a fulcrum for the copper wire to pivot, work harden, and fail.

    And, yes, as a shade tree mechanic, I have done way more than my share of soldered connections.

    A correctly done crimp will create a hermetic seal at the connection point anyway.
    One theoretical question - I'm struggling with this one.

    With the truck's alternator or the RV converter when connected into 120volt/generator, putting a charge into the batteries while driving or plugged in, and the solar panels (which have a controller) also charging, do they work together well - are the amps going in cumulative or would the controller be fooled to think the batteries have more power because of the charging from the alternator &/or PV?
    1) Assuming you are not doing something ridiculous like trying to push 100 amps into a 225 AH battery bank--Then you can connect multiple charge controllers to one battery bank... Which ever charge controller has the highest voltage set point will win the final charging voltage war.

    2) Yes, charge controllers will not "synchronize" when charging a battery bank. And depending on what the charging volt is set for (and available current from the charger--i.e., for solar charger, you need sun)--it is certainly likely that a charge controller will terminate the charge sooner than if it was the sole charge controller. Again, the charge controller with the highest voltage charging profile will set the battery banks' overall charging profile.

    As long as each charger you use is reasonable for charging that battery bank (i.e., Flooded Cell or AGM, etc.)--it will not be a problem.

    For fuel efficicency, a good practice is to run your genset charger first thing in the morning and bulk charge the batteries up to 80-90% state of charge before ~9am... Then let the solar panel take over for the rest of the day.

    Most chargers start to cut back on charging current after the battery is 80-90% charged--so you are left with a genset consuming lots of fuel to push a relatively small amount of current into the battery bank.

    Most generators are fairly fuel efficient down to ~50% load--below 50% electrical load, the fuel flow stays around 50%... So if you are running your genset at 10% to charge an almost full battery, you are using ~5x the amount of fuel for that electricity (50% fuel flow and 10% electrical load).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: Ron's RV Power Questions

    Thanks Bill, excellent tips, explanations and links.

    I was questioning the load draw of the larger inverter vs smaller inverter and received vague answers.... It has a remote on/off switch and a transfer switch so it powers the outlets in the camper when on and when the shore power is not plugged in - with shore power plugged in, the invereter is shut off. Will only plan on turning it on when we need it. It is a Pure Sine Wave inverter - like I said, price was right, but would have been good to get your advice first. We also have a small 150w inverter into a cigarette lighter plug for the small loads like charging up the cellphone.

    The explanation about multiple charging makes sense. Our converter is a Progressive Dynamics 45 amp converter (4 ga wire), smart charger - boost, bulk, float and desulfation - or close to that terminology. So as I understand you, when plugged in to 120v or generator on, I would presume it would take over from the solar. The truck alternator only puts out about 13.4 volts - small wiring from the 7 way connector - so I guess the Solar would be the winner there, on a sunny day. We have a Honda 2000 gen. Good advice for the charge early in the day. We've been handicapped without a battery monitor, so I would connect up the multimeter to check volts - wasn't ideal so hopefully the Trimetric will help.

    That should do me for a bit - I'm sure I'll come up with a few more questions. Thanks again for being there.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Ron's RV Power Questions

    Check the truck alternator (and your meter calibration)--I would expect it to output between 13.8 and 14.2 volts or so... 13.4 sounds too low.

    But you are correct, the long (and relatively small diameter/gauge wire from the truck to the RV will limit charging current to a hand full of amps most likely.

    The Battery Monitor should help you quickly identify how everything works together.

    Let us know how it all works out. There are many more folks out there that can learn from your experiences.

    -Bill

    PS: Typo in previous post--I was trying to type you can connect multiple charge controllers, not "cannot".
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: Ron's RV Power Questions

    Thanks for that Bill - will try to attach a schematic of my plans.
    Ron
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: Ron's RV Power Questions

    Bill, more advice please.
    I've been contemplating adding 2 more 6v to make 4 & 464a/h. A good location would be about 6' cable length from the existing ones. If I wire them together with large enough cable, will this work or what issues might I face?
    Thanks for the advice.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Ron's RV Power Questions

    Several issues... First, when connecting the batteries in parallel, you want the wiring to be equal length (actually equal resistance) between the two parallel sets so that the current is balanced:

    SmartGauge Battery Wiring Examples

    Next, you need to check understand design the cabling to have low enough resistance to carry your heaviest loads. Inverters can take a huge amount of current, so you will need larger AWG wires as the length increases. You can use a voltage drop calculator to figure out the drop (probably a maximum of 0.5 volt drop for a 12 volt bank at the rated maximum power you plan from the inverter).

    Lastly, many people do not, but you should (especially with longer wire runs) use a series fuse (or circuit breaker) near the battery in for each series string to protect against short circuits. High current fuses and breakers are not cheap.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: Ron's RV Power Questions

    Thanks Bill - excellent advice and articles. Planning on options to keep all 4 batteries in the same spot. Will have to make a battery box and ventilate it.
    Ron
  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: Ron's RV Power Questions

    Something that was brought to my attention today on the iRV2 forum is the alternators and voltage regulators produced by Balmar http://www.balmar.net
    These are primarily made for marine use but the programmable multistage regulators strike me as being an answer to care and feeding of both the starting battery as well as the trailer battery.
    I have just started looking at these as a possibility and have not yet delved deeper.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Ron's RV Power Questions

    We have discussed Balmar before here--As I recall, people liked them:

    Google search for Balmar on wind-sun.com forum

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RonShaw
    RonShaw Registered Users Posts: 7
    Re: Ron's RV Power Questions

    Thanks for the link. I have heard of them from the marine world - been around for a long time.
    I've decided on adding two more 6v to make 4, a new battery box and wiring. Just in the stage of gathering together the bits & pieces. Also looking at a 3rd solar panel.
    Tried the 600 w coffee maker with the 1500w inverter. Took 7 mins to brew, voltage dropped down to around 12.6 during the brewing, solar panels (overcast - low sun) only took half an hour to get the batteries (2-6v) back to 100%.
    With an additional panel & 2 more batteries should be pretty comfortable for our usage.