Truck camper 24V system MPP 2424LV-MSD with alternator charging

[Zekan]

Hello everybody!

Will’s YouTube channel and this forum has been a tremendous help for my DIY project. I am in the final planning stages and there’s a few issues I need to clear up before buying all the components. Annoyingly, the 2424LV’s manual does not explicitly state some information that would have been helpful.

My project is an off-grid system for my truck mounted camper based on the MPP 2424LV-MSD with alternator charging. The truck is a regular cab F-150 and the solar system will be installed at the front of the camper, so right by the rear wall of the cab (to give you an idea of the cable lengths). The core of the system will be compact, so most of the cables will be quite short.

Here’s a list of questions I have that I’m hoping you guys can help me with. Please correct me if my assumptions are wrong.

• The 2424LV manual states that the inverter/charged should be connected to a permanent grounded wiring system. This implies that an isolated system is not possible with the 2424LV. The ground screw on the inverter box is for AC out, but it looks to me like AC ground and DC negative will both lead to the truck’s chassis ground through the inverter box unless the AC ground screw is isolated from the DC circuit. Does anyone have any insight here?
• The 2424LV manual recommends 4 AWG and a 100 A fuse/breaker. I used the 125% rule of thumb instead, so I chose a 125 A fuse and upgraded to 2 AWG for the inverter/charger. Should I upgrade the DC ground cable as well to 2 AWG?
• The 2424LV manual makes no mention of a ground-neutral bond and does not explain how the transfer switch functions. I plan on having a floating neutral / no bond. I will not be using a generator. In that case, is it safe to assume that the ground-neutral bond will be handled upstream at the house or the RV power pedestal?
• Based on a few threads here and on other forums, mixing DC voltages for chassis ground is fine.
• Victron Orion cable and fuse sizes are based on the manual’s recommendations.
• 2 pole DC breaker for PV disconnect. Should I use a 2 pole anywhere else or is disconnecting only the positive sufficient?

If you have any comments on my choices of components, please let me know, I’m would love the feedback!

 

[time2roll]

Looks good overall. Yes the main negative bus, the inverter chassis ground, and the ground in the 120v distribution panel will all connect to the vehicle frame. Possibly at separate points.

Battery seems on the small side for the overall package. I tend to skip the switches and just bolt everything direct to the positive bus, your call.

Some of the wire seems oversize but no harm in that.

 

[HRTKD]

What accessories will you have that are 24 volt? I would keep the system simple and stick with 12 volt, but maybe you have an accessory that is only 24 volt?

Instead of a switch to the 24-12 converter, you could put in a Victron Battery Protect. It will prevent the DC accessories from draining the battery. I have one in my system. I set the Battery Protect to cut off slightly higher than the BMS low voltage cutoff. Using my phone, I can turn the Battery Protect on/off. That came in handy one night when the propane detector went on the fritz and decided to set off the alarm for nothing (it was well past it's replace-by date).

 

[Zekan]

What accessories will you have that are 24 volt? I would keep the system simple and stick with 12 volt, but maybe you have an accessory that is only 24 volt?

Instead of a switch to the 24-12 converter, you could put in a Victron Battery Protect. It will prevent the DC accessories from draining the battery. I have one in my system. I set the Battery Protect to cut off slightly higher than the BMS low voltage cutoff. Using my phone, I can turn the Battery Protect on/off. That came in handy one night when the propane detector went on the fritz and decided to set off the alarm for nothing (it was well past it's replace-by date).

I went with 24V because I will be using an induction cooktop. I'm trying to have everything run on 24V if possible. So far, I have only the water pump and ceiling fan that are 12V.

Thank you for the suggestion. The Battery Protect can function as a manual switch as well as an automatic low voltage disconnect? The small advantage I see with a switch is no power draw when in the off position.

 

[HRTKD]

The Battery Protect can function as a manual switch as well as an automatic low voltage disconnect?

Yes, switch and LVD. You can hardwire a physical switch to it using one of the ports. I have the Smart version of the Battery Protect, so I use Bluetooth to turn it on/off.

 

[SVincent]

I am very seriously considering obtaining a MPP 2424LV-MSD (or the hybrid version) for an emergency backup system. Obtaining answers from both ShopSolarKits.com (Tech service rep) and MPP Solar (Taiwan sales rep) to some basic questions has been . . . a challenge. As you have some practical experience with this unit, I was wondering if you could tell me if you have experienced any issues relating to the total Amp-Hr battery capacity that the unit "wants" ? I saw a YouTube video a short time ago where the individual said he said that anything less than 200AH (4-12volt/100Ah bats in series-paralllel) and the unit warned him of "overcharging." I could not tell if he was using SLA, AGM or LiFePO4.

 

[HarryN]

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I went with 24V because I will be using an induction cooktop. I'm trying to have everything run on 24V if possible. So far, I have only the water pump and ceiling fan that are 12V.

Thank you for the suggestion. The Battery Protect can function as a manual switch as well as an automatic low voltage disconnect? The small advantage I see with a switch is no power draw when in the off position.

There are 24 volt water pumps in case it is interesting.

Same for USB outlets.

I assume that you are using a max fan or similar - yes it is annoying that those only come in 12 volt. There are some marine related fans / blowers that come in 24 volt - may or may not fit your use.

 

[HarryN]

I am not completely sure about the value of the midnight solar surge protector in a vehicle application.

For panels that are mounted on a building it makes sense as there is a true connection to the earth.

In a vehicle, usually this does not exist. I have never seen that on a conversion van but maybe I am missing something.

 

[Marcaroni]

I am very seriously considering obtaining a MPP 2424LV-MSD (or the hybrid version) for an emergency backup system. Obtaining answers from both ShopSolarKits.com (Tech service rep) and MPP Solar (Taiwan sales rep) to some basic questions has been . . . a challenge. As you have some practical experience with this unit, I was wondering if you could tell me if you have experienced any issues relating to the total Amp-Hr battery capacity that the unit "wants" ? I saw a YouTube video a short time ago where the individual said he said that anything less than 200AH (4-12volt/100Ah bats in series-paralllel) and the unit warned him of "overcharging." I could not tell if he was using SLA, AGM or LiFePO4.

I am apprehensive about buying anything MPP for a few reasons. First was I sent an email with a few technical questions to MPP and the response did not address my questions and seems like from someone with poor English skills. So I have doubts about any post-sale tech help FROM MPP ITSELF.

Then I noticed that vendors may not offer much support for MPP products they sell. Read for example, Watts247’s varying caveats for certain Mpp products they sell. They offer only 30 days of service, and you deal with MPP for warranty claims. I think I saw one where you must send defective stuff to Taiwan.

So I would say that you really ask the vendor if they will help you when needed.

 

[Zwy]

I went with 24V because I will be using an induction cooktop. I'm trying to have everything run on 24V if possible. So far, I have only the water pump and ceiling fan that are 12V.

Thank you for the suggestion. The Battery Protect can function as a manual switch as well as an automatic low voltage disconnect? The small advantage I see with a switch is no power draw when in the off position.

Use a power converter to run 12V items off 24V. I never turn mine off, it doesn't draw but a few watts idling. I figured it out one time and it would take over 10 years of running the converter to completely drain my 24V bank. You can find my truck camper build link in my signature.

I prefer 24V, lighter wire, less voltage drop and you can use a 3000W inverter easily.

As for bonding, the MPP most likely bonds N-G in the inverter, a simple test by measuring continuity between N and G with all wires disconnected from inverter and inverter off will indicate if N-G bonding is dynamic and internal. If it has continuity, then the unit bonds N-G while under inverter power. This is what you want. I didn't check if the unit has an internal transfer switch, I'd assume it does like the Growatt I use. This is perfect for an RV, you can plug into shore power and the unit will not bond N-G under shore power.

I'm considering upgrading to an induction cooktop and 24V compressor fridge instead of the 3 way we don't use. We use a Dometic CFX95 and I run this off the camper solar system. The Dometic draws about 38W running, and I get ice cream in the middle of nowhere.

For charging off the alternator, I went a different route by adding another alternator and running the output to a 2200W Giandel mounted in the back seat of the truck. From that inverter I used a 30A RV cord and ran it to the rear bumper where I installed a 30A RV outlet. Used the remaining cord to fabricate a short cord to the shore power plug on the camper. This allows me to use the Growatt AC charger. The problem with a 24V system and 12V vehicle system is converting the 12V to 24V can be expensive for a DC to DC charger and the output on 24V is one half the 12V input. Most 12V to 24V DC to DC chargers I've found max out at 20A output. I can easily do 60A.