Looking for Feedback on 400W PV System Design

[JonSchroeder]

Hi Everyone,

I'm in the process of adding solar to our 1984 Sovereign 27 (rear-bath twin). I've pasted a diagram of the system below. I would welcome any and all feedback regarding the design, but I do have a few specific questions I was hoping to get input on:

1) I'm planning to locate the system in the non-curbside closet (hence, the 'vertical' layout shown in the diagram). Any concerns with relocating the batteries from their original location in the front of the trailer? Note that they will be LiFePo4, so no off-gassing concerns.
2) I'm planning to run a 2AWG positive cable to the original DC box which is in the front of the trailer. Would it be beneficial to run a 2AWG negative cable from the DC panel back to the negative bus bar in the closet, or would it be ok to simply chassis ground the DC panel?
3) I'm planning to run shore power (90% of the time this will be a Honda EU2200 generator) through the inverter (Victron MultiPlus 12/2000) at all times. Any reason not to do it like this?
4) I'd like to add a battery isolator and connect the system to tow vehicle power for charging. I haven't figured that part of the system out yet, but any feedback on how this should be done would be appreciated.

Thanks in advance,
Jon

[rickst29]

Jon, this looks very good - you've done your homework well.

WRT your question #2 ("A new and separate "Ground" wire from the DC Distribution "Ground" Bus, back to the new high-current closet "Ground" Bus?") I have just two concerns which could justify making this new connection.

First, note that these frame lugs connect different metals, and any exposure of that actual connection to an electrolyte (such as most air, especially ocean spray) will cause the steel side to rust quite fast. (The copper side acts as the cathode, this is "galvanic corrosion".) And second, vibration of the frame during travel could tend to screws holding them together. And of course, any developing rust will weaken the screws more.

Second, I see that you are expecting to draw up to 100A through that DC Distribution panel. That amount of current makes the return path more critical. Will you really be needing all of that, when you have 120VAC available from the Multiplus?

[rickst29]

But I'll answer here anyway.
- - - - - -
For charging from a TV, you could buy one of these: https://www.renogy.com/renogy-12v-dc...ttery-charger/. It contains a DC Boost Converter (boosting low Voltage from the Tow Vehicle) followed by a PWM Solar Charge Controller which reduces the boosted Voltage back down... into something your batteries can use, based on SOC. You would set DIP switches to specify charging mode == 14.6V Lithium.

Very easy to install. The only possible problem (which might actually be very likely to occur, if you buy the 40A model), is burning your Bargman cable or TV wiring. It won't reach 40A output, being power-limited @ 500W. But 500 output watts, divided by 90% efficiency, and then divided by Bargman Cable endpoint Voltage as low as 11.0V (after huge "wire losses" generating heat within the cable, due to high current) requires the unit to draw about 50A through the cable. YIKES.
But, if the the 20A 250W version would be sufficient for your needs, it should be OK on your current AS cabling.
- - - - -
Before these cheap Renogy "Bargman Converter/charger" devices came on the market, I did a "build from scratch" version of my own. But in my version, I put the Voltage Booster in the Tow Vehicle, allowing up to 500W of power through the Bargman at 1/3 as much current (higher Voltage).

Within the Trailer, I already had a nice MMPT Solar Controller. A "detector Relay" sees that Voltage on the Bargman "Trailer Battery Charge" has increased to high value, and it switches another Relay. The second Relay switches the MPPT "Solar "+" terminal from the 3*120W "genuine" solar panels on the roof (360w max, 65V total in series) and connects the "fake" solar panel on the Bargman cable (about 500W max, 36V appearing as a single big panel.)

In comparison to Renogy, I have almost no Voltage drop "wire losses" and waste heat going out of the cables. I also cost a lot less, because I used a better "Solar Controller" which I already have (and use quite a lot in the normal way). The cost? Far less money, but a lot of "new stuff" to install inside the Tow Vehicle. (The trailer mods are comparable to installing the Renogy.) My way takes a lot more time.

[JonSchroeder]

Regarding your response RE ground wire vs. chassis ground: Great points.
Sounds like it will be safer to run a negative wire back to the system neg. bus. Since I'm already running the pos. wire, that really won't be much extra work (just a few more $$$, but who's counting at this point...).

Your point about needing 100amp service to the DC panel is also a good one. Considering that the current fuse size from the battery is only 50amp, i can't imagine why I would need to go higher than 50 amp. That being the case, seems like 4awg wires (pos. and neg.) should probably do the trick!

Thanks again for the input. Very helpful!
Jon

[JonSchroeder]

Regarding your tow vehicle charging response: Seems like the Renogy 20A DC-DC charge controller would be a very simple solution. Two follow up questions for you (if it's not too much trouble):

1) would I need any kind of a relay or automatic transfer switch to avoid charge coming from multiple sources at the same time (ie, PV + TV)? Alternatively, would I just disconnect the panels from the system when charging from the TV?

2) Since I'll be charging by PV while driving, do I really need the ability to charge from the TV? Seems a bit redundant, but I could be overestimating the charge I'll get from my panels.

Thanks again Rickst29.
Jon

[rickst29]

Originally Posted by JonSchroeder

Two follow up questions for you (if it's not too much trouble):

1) would I need any kind of a relay or automatic transfer switch to avoid charge coming from multiple sources at the same time (ie, PV + TV)? Alternatively, would I just disconnect the panels from the system when charging from the TV?

No. The Renogy, and the better but much more expensive Redarc, are both built to take from both sources simultaneously. No external relay or switching is required.

Originally Posted by JonSchroeder

Since I'll be charging by PV while driving, do I really need the ability to charge from the TV? Seems a bit redundant, but I could be overestimating the charge I'll get from my panels.

The Panels are only effective under clear skies between roughly 10:00AM - 4:00PM (daylight time) in Summer. Shorter days with lower sun angles (Early Spring, Winter, Fall) perform much worse. Cloudy and rainy days get virtually nothing. For boondocking, you need to have an alternate power source.

[ghaynes755]

Jon you will need the Victron Digital Multi Control for running the Multiplus. Lots of great diagrams available with other information at www.amsolar.com. Victron makes the Cyrix-ct for the charging line through the tow connector.

AMSolar also has a smart transfer box that might be of interest. It eliminates the need for a sub panel.

[waninae39]

this is our design with mostly victron parts

we have 350W solar with three panels(two on the roof, one hinged on the back side )

be sure to get a shore line power surge protector. it has save our bacon many times

BTW, we have three victron displays
- bmv712
- colour monitor
- mulitplus control panel

[JonSchroeder]

Thanks for the additional recommendation/info ghaynes755 & waninae39. Regarding the need for a multiplus controllers, I was hoping to leverage bluetooth (I ordered the multiplus bluetooth dongle) along with the VictronConnect app (for mac) for setting up my systems. It's my understanding that the latest version of that app allows for setting 'basic' system parameters (ie, charging conditions, AC disconnect/connect voltages, etc.). Since my system is quite simple, this seemed like it should work for me. Are there important parameters that you don't think i'll be able to control and/or monitor using the victron connect app?

Note that the app includes 'demos' of pretty much all of their equipment, so I'm able to explore the settings before my dongle gets here. Quite a nice feature.

Thanks again,
Jon

[uncle_bob]

Hi

The Victron Multi 3000 is virtually the same price as the Multi 2000. If you have space for it, there is no real reason not to put in the 3000. I had space issues with my install so indeed I have a 2000.

With any inverter "surge" is part of the issue. Running 2/0 cable is probably better than running something smaller. Victron recommends 4/0 for both the Multi 2000 and the Multi 3000, for the 2000 I think that is overkill.

You will need a fuse at both ends of the cable to the batteries. One fuse protects the wire from the power out of the charger side of the 2000. The other fuse protects the wire from the power out of the battery. With both of them in place, a short is much less likely to start a fire.

There is absolutely nothing wrong with a rotary switch for a battery disconnect. I happen to be lazy so I went with the Blue Sea 7000 solenoids for disconnect. Push a button and it's done. Indeed it also lets the wife spot the red LED on the switch as you exit the trailer and ask "did you disconnect the batteries?" .... I have data on this ....

One other thought. As you do this, you might think about allowing space for more batteries. I'm not suggesting you have to put them in right now. Only that they just *might* be something to plan for.

Bob

[JonSchroeder]

Hi Bob,

Thanks for the feedback. I went with the 12/2000 thinking for the size of my initial bank and PV, anything bigger would probably be overkill. Knowing that the MultiPlus units can be paralleled, I figure that if (when) i'm ready for more power, I'll probably go that route (i should have plenty of space for a second 12/2000 in the closet).

Regarding space for more batteries, this is one reason why I relocated to the road-side closet. I can fit three (possibly 4) battle born 100Ah's on the closet floor. Plus, if I want to expand beyond that, I have space for at least two more in the access hatch area under the twin bed. Can't imagine I'll need (ie, be able to afford...) more than 400Ah of lithium.

Really great point about the fuse at the battery terminal to protect the wire from a short. Completely missed that one.

Thanks again for all the help!
Jon

[waninae39]

we have space for two BB lion battery under the bed. that takes the space of 1 of 4 containers.

+ve. this takes a load on the tongues as the BB are lighter and moved closer to As center

-ve, 25% less space under the bed in the AS22FB. if i take up any more storage space, i may get shot

[uncle_bob]

Originally Posted by waninae39

...... if i take up any more storage space, i may get shot

Hi

Pretty much exactly what got two of our batteries out on the tongue. The other two going into "dead space" under the sofa didn't have any death threats associated with them either

Bob

[rmkrum]

Fuses to protect the wiring downstream of any high current battery is a darn fine idea.

Blue Sea Systems makes ones that bolt right on the 3/8 inch battery terminals. Look on Amazon for the hardware and appropriate fuses. Select a fuse to protect the wire size.

Easy and helps with safety.

[57Vintage]

I have the Multiplus 3000, not familiar with the 2000. On the 3000 there is a separate grounding lug that should go directly to ground (not to be confused with the 12 volt and 120 volt negative terminals).

Since mine sets directly over the frame rail, I took a small hole saw (narrower than the frame rail) to cut through the floor. Then drilled and tapped for a stud in the frame rail and ran the 3000 ground lug directly to that. A serrated nut tightens the stud into the frame rail. Above that I double nutted the stud with a serrated nut upside down, to create more surface contact for lugs, and put a serrated nut on top of the lugs.

[uncle_bob]

Hi

The 2000 and 3000 are very similar units. The outer dimensions are the biggest difference between them. The 2000 has the same "ground point" on it.

One other note on the 2000 / 3000: To fully set them up you need a special programming dongle from Victron. It's not expensive, but getting it to work is a chore. The instructions are "less than ideal" in terms of describing the sequence that *must* be used to get it to recognize the unit. Each time I use it I mean to write down the sequence that *finally* worked

Bob

[JonSchroeder]

I’ve been trying to figure out the best way to ground the equipment (MP2000 and MPPT) as well as the system Neg to the chassis. A small hole over a frame rail and a tapped hole in the rail seems like a great idea. Thanks for that tip Vintage57. Now I just need to find a good spot to do that. Fingers crossed there happens to be a frame rail under that closet...

Regarding the dongle: I’m a Mac user, so I was quite relieved to see that the VictronConnect app was recently updated to add Multiplus control. With the MK3-USB dongle, it connected to my Mac on first try and seems to have all the settings controls I need for my relatively simple setup.

Here a couple pics of progress to date:

[uncle_bob]

Originally Posted by JonSchroeder

I’ve been trying to figure out the best way to ground the equipment (MP2000 and MPPT) as well as the system Neg to the chassis. A small hole over a frame rail and a tapped hole in the rail seems like a great idea. Thanks for that tip Vintage57. Now I just need to find a good spot to do that. Fingers crossed there happens to be a frame rail under that closet...

Regarding the dongle: I’m a Mac user, so I was quite relieved to see that the VictronConnect app was recently updated to add Multiplus control. With the MK3-USB dongle, it connected to my Mac on first try and seems to have all the settings controls I need for my relatively simple setup.

Here a couple pics of progress to date:

Hi

Both the positive and negative leads come down off the roof and go into the MPPT solar controller. Neither one is grounded anywhere. Nothing on the roof gets grounded.

The frame of the Multi gets grounded to the same bus structure that ties the 120 V and 12V to the frame of the trailer. There are multiple bus bars scattered around the trailer doing this. Simply ground the multi chassis to one of them.

All return lines (12V negative) get a cable all their own to route back to the battery. The chassis does not get used for this. Indeed there are ties for safety, but the normal design is to route the negative current through cables.

120V ground all gets done at the breaker panel. The ground on the transfer switch and it's tie to neutral is detailed in the Victron manual.

Bob

[JonSchroeder]

Hi Again Everyone,

I'm in the final stretch of of the install of my system. I'm trying to test each part of the system as I go to look for potential issues. Yesterday, I got the wiring to the DC panel finished up. To test functionality, I ran a couple of tests. First, I turned all the lights in the trailer on (about 180 watts total draw). Then, I ran the fridge on DC for a while (about 250 watts). Everything worked fine, but I noticed the Neg bus on the DC panel was getting quite warm with the fridge running. On further inspection, it seemed to be the non-insulated grounding wire that was getting hot (so hot I couldn't keep my finger on it for long).

Does this make sense? Shouldn't the fridge have a neg. wire running back to the panel? Or could this just be chassis grounded?

Note: I haven't added a chassis ground at the new battery location yet, but I do have a 4awg neg cable running from the DC panel to the new battery location. That cable didn't get warm at all when running my DC tests.

As a reminder, this is a 1984 Sovereign. Pic of the DC panel pasted below.

[daleyocum]

I can’t help with the issue of the ground wire heating up in your older trailer but I can say in newer ones the chassis isn’t expected to conduct significant power. Airstream always runs both a positive and a negative to every device. This avoids ground loops and corrosion problems. If yours IS using the chassis as the negative for some devices yes you will need a more significant wire going to the chassis.

We use our Victron multi control panel several times a day to turn and off the inverter. You’ll want one too. It allows anyone in the trailer to quickly turn the inverter on and off as well as set the current the system is allowed to draw from shore. It really is necessary.

You’ll also want a battery monitor, like the Victron BMV712. Without it none of your equipment will know the state of charge of your Lithium batteries and thus won’t know when to turn off. They are able to figure it out just by voltage with AGM or other Lead acid batteries but Lithium has such a flat discharge curve they need help.

When it comes to adding more Lithium later, I wouldn’t wait too long. Ideally you want lol of your batteries in parallel to have roughly equal characteristics. If you, for example, added two new batteries to two old batteries several years later they’ll have different capacities with unpredictable results. I started out with 300ah and then added another 200ah the following season and it seems fine but I’m glad I didn’t wait multiple seasons to upgrade.