RV solar & electrical - Charging questions & general advice?

PNW_Steve

Good Morning Everyone,

I am in the process of converting a bus into an RV. This is not my first and I though that I had a pretty good handle on the electrical side until I threw solar and "Over the Road" charging using a battery isolator in conjunction with the coach charging system.

My past projects have relied on a single charging source for the house batteries and I am concerned about potential issues when using three different charging sources: RV converter/charger, Solar and Coach charging system. Any advice in this area would be appreciated.

I would also appreciate any input regarding my general design. I have been tinkering with this stuff for a few years but his is my first "real" solar install.

My intention is not to be totally grid independent but instead to use the available solar to reduce generator run time when I am not plugged in as well as supporting only the refrigerator when parked for extended periods in a sunny location.

I have another rig that I installed a 10.7 cu.ft. refrigerator that runs on battery/inverter. No solar just the generator or shore power to recharge. Not ideal but functional. This fridge has an Energy Star estimate of around 400kwh/year. I have measured an actual consumption of .5-.8kwh daily. I can run it overnight on a pair of golf cart batteries without a problem (2x6v-190AH).

I have not measured the consumption of the 5.5 cu.ft. refrigerator but the Energy Star estimated annual consumption is 15-20% lower.

I am building out to accommodate two Trojan j-185 batteries but due to initial budget I will likely only install one to get started.

I have spec'd  a 40A MPPT controller that (as I understand) can accommodate  running either 12v panels in parallel up to 40A capacity or series pairs of 12v panels paralleled up to 40A capacity. I plan on starting with two pairs (4) of 12v/100watt Renogy panels and adding a third pair next year.

I will attach a draft drawing of my system. Below is a list of components:

Item	Description	Link
Refrigerator	Igloo 5.5 cu.ft. 338Kwh / year	https://www.walmart.com/ip/36758017?wmlspartner=wlpa&adid=22222222227026396574&wl0=&wl1=g&wl2=c&wl3=42531716792&wl4=pla-81188469872&wl5=9033354&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=online&wl12=36758017&wl13=&veh=sem#about
Inverter	?? 3kw Pure sine wave – undecided	https://www.amazon.com/dp/B0131PZ9J2/ref=wl_it_dp_o_pC_S_ttl?_encoding=UTF8&colid=KH7SFUD03QTA&coliid=I12HV2CG4GULG8
Inverter ATS	DIY 20A transfer
Main ATS	30A ATS	https://www.amazon.com/Go-Power-TS-30-Automatic-Transfer/dp/B00153EYTO/ref=sr_1_1?ie=UTF8&qid=1478450483&sr=8-1&keywords=30+amp+transfer+switch
Converter	55A Converter/3stage Charger & load center	https://www.amazon.com/dp/B004BC59S6/ref=dra_a_rv_lb_hn_xx_P3148_100?tag=dradisplay-20&ascsubtag=e6f529f219a88518022c6687c20d531b_S
Battery Isolator	140 Amp Isolator	https://www.amazon.com/NOCO-IGD140HP-140-Battery-Isolator/dp/B001DKRF2M
Generator	Champion 3100 Inverter Generator	https://www.amazon.com/Champion-Power-Equipment-75537i-Generator/dp/B00JZQUSAC/ref=sr_1_1?ie=UTF8&qid=1478450308&sr=8-1&keywords=champion+3100+inverter+generator+remote
Battery	1 or 2 Trojan J-185 or equiv.	http://www.trojanbattery.com/product/j185p-ac/
Solar panels	4x Renogy 100 Watt	https://www.amazon.com/Monocrystalline-Photovoltaic-Module-Battery-Charging/dp/B00V4844F4/ref=sr_1_8?ie=UTF8&qid=1478450604&sr=8-8&keywords=renogy+100+watt+solar+panel
Charge Controller	Renogy 40 A MPPT	https://www.amazon.com/Renogy-Tracer-Charge-Controller-100VDC/dp/B00E7NI9PE/ref=sr_1_1?ie=UTF8&qid=1478450679&sr=8-1&keywords=40+amp+mppt

 

PNW_Steve

Here is the link to the electrical design: https://drive.google.com/open?id=0B0r8AcTUU9thZXRVVjRBODdiVzg

Also, the reason for the 3kw inverter is to support the occasion that I need to run the coffee maker, microwave or clothes iron when I am unable to run the generator. That will be a rare occasion and a short duration load.

BB.

What are you expecting from Solar? A reasonably sunny area (non-winter, no coastal overcast/fog) may get a minimum of ~4 hours of "noon time equivalent sun" per day... A 400 Watt array will produce (no shade):

• 400 Watts * 0.52 off grid system eff * 4.0 hours of sun = 832 Watt*Hours (0.8 kWH) per day

A 3 kWatt AC inverter may take 20+ watts just "turned on" (20 watts * 24 hours per day = 480 WH per day)... That is about 1/2 of your present (wild guess) solar production (spring/fall).

The battery you are looking at is 12 volts @ 205 AH (20 hour rate)--At best, a single battery would "reliably" run a ~500 Watt AC inverter at full rated power (plus ~1,000 Watt surge load for a few seconds). To run a standard energy star refrigerator, you would probably need a minimum of 2-3 of that class battery to reliably run the fridge (they have ~>600 watt of surge current to start the motor, and 500-600 Watt AC defrost heater).

Anyway--Before I go too far down this rabbit hole--I suggest getting a very good handle on your loads... And look at "extreme" energy conservation (if you want to run from solar/battery bank). And--For RV usage (unless you are going to live full time off grid)--Perhaps propane fridge (plus stove) would be a better fit. If you are committed to a standard fridge--Then, looking at the solar power system more closely and be ready to commit more space/weight to battery bank and solar array. And/or prepared to run genset/shore power more.

-Bill

PNW_Steve

PNW_Steve said:

Also, the reason for the 3kw inverter is to support the occasion that I need to run the coffee maker, microwave or clothes iron when I am unable to run the generator. That will be a rare occasion and a short duration load.

PNW_Steve said:

 
My intention is not to be totally grid independent but instead to use the available solar to reduce generator run time when I am not plugged in as well as supporting only the refrigerator when parked for extended periods in a sunny location.

I have another rig that I installed a 10.7 cu.ft. refrigerator that runs on battery/inverter. No solar just the generator or shore power to recharge. Not ideal but functional. This fridge has an Energy Star estimate of around 400kwh/year. I have measured an actual consumption of .5-.8kwh daily. I can run it overnight on a pair of golf cart batteries without a problem (2x6v-190AH).

I have not measured the consumption of the 5.5 cu.ft. refrigerator but the Energy Star estimated annual consumption is 15-20% lower.

softdown

You need a smaller inverter and a larger battery bank. Forget using electricity for cooking, propane is perfect. Get the smallest microwave that you can...I have seen 800 watts and suspect that 600 watts is available. Ironing? Get the smallest one you can find.

 I would try to get by with a 300 or 600 watt inverter. Their surge capability is often double their rated capacity but that must be verified. Trying to run an electrical fridge with a smallish array is asking for problems.

I come across a bit harsh at times though that may be the best medicine.

BB.

If you pick the right devices, you can get your peak microwave/coffee maker/iron to ~1,100 watts or less... That gets into a 1/2 as large AC inverter (1,500 Watts) pretty easily. And you can stick with a 12 volt batter bank (other house loads)--Unless your chassis is a 24 volt system--Then you may want to look at a 24 volt house bus too.

To run everything at once is just a huge draw on a 12 volt battery bank. For example a 3kW AC inverter (remember ~6 kWatt surge for a few seconds is 2x the current):

• 3,000 Watts * 1/0.85 AC inverter eff * 1/10.5 volt battery cutoff (less than full battery, wiring drop) = 336 Amps of current

That is not a small amount of current. 1,200 Watts of load on a 12 volt battery bus is nice--Some folks run 1,500 to 1,800 Watts peak and are happy with that.

-Bill

PNW_Steve

Thanks for the input,

I left out a couple of details to try and avoid confusion.

I will also need to OCCASIONALLY run larger loads at times when I cannot run the generator. Along with the iron and coffee maker mentioned I will have to support a commercial sewing machine and serger.  Not optional. No "Energy Star" model available. 

As far as running a 600-1200watt inverter, even without the loads mentioned above, that will not come close to  running just my refrigerator. With inductive loads, such as refrigerator compressors or other electric motors, you require a startup capacity that is MUCH greater than the running load. If I recall, my running load on my last fridge was around 350 watts. I tried a 600 watt and a 1500 watt inverter that I had on hand before I bought the 2000 that is running that fridge today.

The bus has a 12v charging system so 24v is not practical. If I were looking at a solar install larger than 600 watts it may have advantages but I am not. 

I understand that batteries are not infinite sources of energy. I understand that with the batteries that I am looking at that I will have a bit less than 1kwh of available energy on a full charge. If I maxed out that inverter (load) I would be lucky to get 15 minutes run time. That is NOT what I am trying to do. 

I will be adding solar, battery and inverter to SUPLIMENT shore power and generator power. Not replace them. I understand that one j-185 battery is not ideal. I intend to make allowances for a second one as budget allows. I could leave out the solar panels and that would make room in the budget for a second one. Somehow I suspect that may not work very well....

I did ask for general input and I do appreciate it. My biggest questions involve the care & feeding of those $300 a piece batteries. I have assembled similar systems in the past but with only a single source of house battery charging. 

What kind of pitfalls or concerns should I be looking at when considering connecting: solar, converter/charger and coach (OTR) charging?

Any thoughts regarding the solar panel / charge controller configuration that I have spec'd?
Yes, I would love to install more that 400 watts initially but again budget dictates a modest starting point. 

Thanks again.

S.

westbranch

you want to check out the output from that CONVERTER....  mine was not suitable for a decent recharge, so it is  solar all the way unles we have shore power and the Xantrex True charge comes out...

PNW_Steve

westbranch said:

you want to check out the output from that CONVERTER....  mine was not suitable for a decent recharge, so it is  solar all the way unles we have shore power and the Xantrex True charge comes out...

From the manufacturer:

The WF-8955 model provides 55 Amps and a clean, constant 13.6 VDC nominal output, for reliable operation of electronics and appliances. Automatic three-stage charging extends the life of your battery with output voltage modes of 13.2 VDC range “float” mode, 13.6 VDC range “absorption” mode, and a 14.4 VDC range “bulk” charge mode. The 8900 Series also maintains peace and quiet, as the cooling fan runs only when needed.

Converter Type	Three-Stage Converter Charger
Output Current	55 A
Voltage Output	13.2 – 14.4V DC Range
Absorption Mode (Nominal Voltage)	13.6V DC (nominal voltage)
Bulk Mode (Quick Charging Voltage)	14.4V DC (quick charging voltage)
Float Mode (Trickle Charge Voltage)	13.2V DC (trickle charge voltage)
Over Current	Yes
Over Temperature	Yes
Over Voltage	Yes
Reverse Polarity	Yes

PNW_Steve

Is the answer to your question regarding the output answered in that info? I am not sure exactly what details regarding the output you were concerned about.

This is not an old school "buzzbox" that you see in many older RV's.  It claims to be a "modern 3 stage intelligent" charger. I have no first hand experience with this one but it is very well reviewed and I have talked to folks that have replaced their old units with one from the WF-8900 product line and they raved about apparent increased battery capacity after installing the WF-89XX. That would give me some indication that it is doing a superior job of giving the batteries a full charge.

Thanks.

S.

westbranch

Steve, sorry they don't answer my  concern.  What batteries are you using for the solar side?  The major manufacturers have absorb  and Float numbers that are higher than what that unit will provide...  see this for example about the bottom of page 1 http://www.trojanbattery.com/pdf/datasheets/T105_Trojan_Data_Sheets.pdf... I note that there is no Equalization charge option on that unit either...

I agree the users of those converters would have seen much better battery performance especially if they were using 'car' batteries as that is the norm for those batteries'

PNW_Steve

westbranch said:

Steve, sorry they don't answer my  concern.  What batteries are you using for the solar side?  The major manufacturers have absorb  and Float numbers that are higher than what that unit will provide...  see this for example about the bottom of page 1 http://www.trojanbattery.com/pdf/datasheets/T105_Trojan_Data_Sheets.pdf... I note that there is no Equalization charge option on that unit either...

I agree the users of those converters would have seen much better battery performance especially if they were using 'car' batteries as that is the norm for those batteries'

One of the gents I was talking to regarding this converter is running 4x Interstate golf cart batteries. 2 pairs in series/parallel for a 12v 380AH battery bank. I would suspect that going from a really crappy converter to a "less crappy" one is likely to help regardless of (reasonable) battery type. He was VERY happy with the improvement that he saw when he replaced his old converter with the new one. 

I understand the lack of adjustable set points for charging and the lack of equalization are downsides. The solar controller does have these features.

This is where the root of my biggest questions lie. The converter charge settings are conservative and are not ideal for the spec'd battery(s). How would the solar controller interact with the converter? I have never placed a line powered battery charger on a solar battery bank to observe how they respond.

An example:

I am plugged into shore power overnight with the batteries charging from the converter. They receive as complete a charge as the converter is able. In the (sunny) morning I hit the road and am reliant on the solar charger to top off the batteries. The output from the solar array should outpace the DC load by a good margin allowing charging per the MPPT controller setup.

If it plays that way then the features of the MPPT controller would substantially offset the shortcomings of the converter.

BTW: P-185 not T-105 one T-105 would not play very well in this setup........ 

PNW_Steve

I just spoke with the MPPT controller manufacturer. Their advice was to simply connect the MPPT controller in parallel with the converter and when the converter fails to give the batteries an ideal full charge the MTTP controller would pick up the slack and finish charging.

If budget were no issue I would not be using the RV converter. I would buy the best charger that I could find and have custom 12v and 120v  breaker panels made by a local marine shop. It would only cost me another thousand bucks. Most all of us would love to drive Ferrari's. In reality some of us drive old used Ford's....

westbranch

T 105 was just the first one I got the charging table for, just an example...  you are right about a poor match, they would not play well together...

 If I knew then what I know now I would be looking at real robust chargers, that are designed and built for solar systems and stay away from the 'smart' chargers, they are best fit for a dying car battery...  a bad cell killed one that I have, it let the magic smoke out!
I trusted my Campers 'converter' to 'do it right' one time and after 3 days charging,  the house battery is DEAD  out at the lake..... well no shower that night, no LED reading lights either.  The battery had needed an EQ to revive it... not a love tap...

YMMV

softdown

PNW_Steve said:

I just spoke with the MPPT controller manufacturer. Their advice was to simply connect the MPPT controller in parallel with the converter and when the converter fails to give the batteries an ideal full charge the MTTP controller would pick up the slack and finish charging.

If budget were no issue I would not be using the RV converter. I would buy the best charger that I could find and have custom 12v and 120v  breaker panels made by a local marine shop. It would only cost me another thousand bucks. Most all of us would love to drive Ferrari's. In reality some of us drive old used Ford's....

I just bought a '93 GMC box truck with torn up seats and a mirror that is prone to falling off. With a 454 to boot. I need to use it about four times to move my stuff from Denver. In$urance company wants over $50/trip. I can see where they are coming off but I am still balking at that. I may just wait until springtime and better weather...

My old guru did the parallel with the charge controller...he is old school. The system works great, it is the batteries that can be a pain. Opinions vary on most everything.

Most of us are on limited budgets. A few here are pretty well off. A few here sell and install to the pretty well off...