What makes the most sense for my bus conversion build?

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Matthew Woods asked Mar 15, '21

What makes the most sense for my bus conversion build?

Howdy! I'm looking for a little help as I've figured out the beginning and end of my solar set-up but it seems like there's multiple ways to fill out the middle. I was originally piecing together a build based off of youtube but I like the idea of a mostly victron system where I can still cheap out on a couple of the components.

Here's what I'm working with so far:

4* 400W solar panels (50.4V / 10.18A)
24v Lithium battery bank

My panels are going to be wired in series so I've been eyeing up the EasySolar II since it seems capable of handling the 200v input from the panels. I will be using 120VAC and 12VDC in the bus so I need to figure out the best way to handle the 240VAC output from an easy solar II unit.

Alternatively, it seems like I could just get a 250|70 mppt solar controller and work that into a cheaper 2000W 24V inverter connected to a battery monitor and then the battery bank.

Will there be a 120v easysolar ii coming out? Is there a different product(s) that makes better sense for assembling my system?

Side question: how feasible/complicated/expensive would it be to integrate my 24v solar power system with the 12v system of the schoolbus?

Thanks in advance for any insight!

EasySolar All-in-One offgrid solar Help

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Answer 1 · 2021-03-15T04:02:32Z

Kevin Windrem answered · Mar 15, 2021 at 04:02 AM

Look at the open circuit voltage at LOW TEMPERATURE. PV panel voltage goes up as temperature goes down. 250 might not be enough with 4 panels in series.

There are no combo units sold by Victron that handle 120 volts AC. You'll need to use a Multiplus. Either the Compact for 2000VA or the large package size of the 3000 VA depending on your load needs.

The only other way is to use transformers in and out but that doesn't make sense from a size, weight or cost standpoint.

No word on what new models might be available for the US 120 volt market.

You must match the inverter's DC input voltage with that of your battery bank. That said, you can use a DC-DC converter to make 12 volts for your DC loads from a 24 volt battery bank. But for a 2000 watt system, I'd just stick with a 12 volt battery bank.

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Matthew Woods commented · Apr 01, 2021 at 06:48 AM

I checked the low temp voltage and ended up following the other posters advice. Going to run 2 sets of 2 panels. Settled on the multiplus as well.

There are 4x 12v lead batteries on the bus as it stands currently, I think I'm better off leaving that system as is and having my 24v solar kit largely separate besides perhaps charging off the alternator if I can wrap my head around that.

Thanks for the reply!

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Answer 2 · 2021-03-15T06:21:09Z

Vance Mitchell answered · Mar 15, 2021 at 06:21 AM

I would choose the 3000va Multiplus and 2x 150/35 Smartsolar controllers.

The larger multiplus will give you more flexibility later on. (In my motorhome I started with the 1600va compact unit and soon upgraded to a 3000va due to loads.)

Using 2 separate mppt controllers will be slightly more shade tolerant and will give you some redundancy if something ever fails.

For converting 24v down to 12v there is a few options,

The Orion smart (24/12)would be the best choice allowing proper charging of your 12v batteries.

A smart charger ran from the inverter would be another option and allows you to use it for charging other batteries.

Then there is the orion dc-dc converters (non-smart) which will supply power to your 12v circuits but won't properly charge your batteries at the same time.

As for charging your 24v batteries while driving,

another Orion smart (12/24 this time) could be used and would limit the charge rate to prevent damage to your alternator.

There is multiple ways to handle each piece of the puzzle, which one is best for you can be difficult to determine.

The best thing you could do would be work out all your loads (and how and when you will use them) then have a chat with your local dealer. They might have another solution that will work even better for you.

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Matthew Woods commented · Apr 01, 2021 at 06:45 AM

Okay thank you very much for the response! I went ahead and got myself a multiplus 3000 and the 2x 150/35 smart controllers. Additionally I have a mk3-usb which i understand is used to connect to a computer for set-up/updates. I also have the BMV-712 smart battery monitor. My main hang-up at this point is figuring out the best option for integrating a DIY battery into the system. I am considering using an Overkill BMS but I'm not sure if that operates on it's own or if it is Victron compatible - other threads seem to be able to make it work.

The components I need to figure out:

DC-DC converter (24/12) for wiring leds/fans/etc- does it need to be smart? isolated?

DC-DC converter (12/24) for charging 'house' batteries with alternator

Isolator? somewhere in there? lol

Accessories for the multiplus- do i need temp/voltage sensors that go on the multiplus if the 3rd party BMS has low-temp protection already?

Am I missing a particularly useful/necessary component to my system?

Thanks for any help!

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Vance Mitchell Matthew Woods commented · Apr 01, 2021 at 07:44 AM

I don't have any experience with the overkill BMS but my thoughts are as follows.

The BMS should be used as a safety device more than a controlling device. If the Multiplus and Smartsolar units are configured to stay inside of the BMS limits it shouldn't cause any problems.(ie if the BMS High voltage is set to 29.2V keep your charge voltages below 29V - From memory Victron recommend around 28.2V . And your Multiplus Low voltage disconnect should be higher than the BMS cutoff)

Low temperature charging can however be an issue depending on where you are and where in your bus the batteries are located. (The multiplus comes with a Temperature sender and can be set to stop charging at low temperatures)

Victron have some really good examples of system wiring which include Isolators and fuses, but if you are not sure then please consult a dealer to confirm requirements for your location.

This would be a good starting point

Your 24-12 reducers can be fairly basic, normally you would have a common negative in a bus and as it is not charging a battery you don't require a smart version. Personally I wired my bus as 24V and then added smaller 24-12 reducers anywhere they are required.(My bus was 24V originally though)

For charging your house battery while driving you have a few options depending on how much power you wish to transfer.

If you expect to need a lot of charge whist driving, I would consider if a separate alternator could be fitted, (not cheap for lithium compatible)

Next best option would be the smart 12-24 converter as it has the necessary charge profiles for your battery.

Another option which is possibly not recommended, is to use a seperate 12V inverter and have it's output going to the Multiplus input. (I am interested to hear others opinion on this)

That last option is not the most efficient, but I would be interested to know how it compares to an Orion 12-24 Smart. (cost, Efficiency and redundancy)

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