Split-Phase 120/240V and High Output Alternator

[AdventureBus]

Hello folks,

I have been planning the electrical system for my rugged adventure bus and would like some feedback on my design. This is a simple diagram and does not include all of the wiring, fuses, switches, etc. that is will need but serves as a preliminary planning tool.
Link to my build thread: https://forum.expeditionportal.com/threads/international-3800-adventure-bus-build.219248/

Some things I desire from my system:

• Ability to power 120/240V split-phase dual head mini-split while on the road
• Enough alternator and battery bank capacity to be conservative with power demands

Unique features of this system not found in most RVs:

• Converting alternator power to split-phase 120/240V and passing it through the AC input of the Multiplus'
• Multiplus' stacked and configured for 120/240V split-phase output
• Ability to utilize Multiplus PowerAssist feature to supplement alternator/inverter power with LiFePo4 house bank
• 4 position switch for 50A split-phase 120/240V input, 30A/50A single-phase to split-phase input via Autotransformer, 6000W split-phase 120/240V input from alt/inverter
• Multiplus' will always be supplied with split-phase input and thus shouldn't need software configuring when changing input switch

Issues to mitigate (need help with this):

• Need to protect alternator from overworking/overheating
  • Plan to use Wakespeed WS500 and regulate alternator output with temperature sensors and conservative expectations
• Need to protect alternator and other components from load dump from LFP BMS disconnect
  • Will the starting batteries provide an adequate buffer for voltage spikes from load dump?
  • Alternator will have avalanche diodes
  • Will probably use Sterling alternator protection device as additional insurance

 

[Alloy]

You understand the loss that will be incurred putting a system like this into a bus?

I don't understand the purpose of the 6000w inverter?

 

[AdventureBus]

You understand the loss that will be incurred putting a system like this into a bus?

I don't understand the purpose of the 6000w inverter?

Are you saying there will be electrical efficiency loss or financial loss?

The purpose of the 6000w inverter is to pass through the Multiplus inverters. They would be able to tap the house bank to provide PowerAssist and 4800 additional watts of continuous output until the batteries were depleted. I would only need a fraction that capacity for normal use.

 

[llamalander]

I'm having a hard time seeing why you need so much output, do the windows close?
Looked at the build thread, obviously you're not afraid of engineering solutions, but I don't see the problem that 240v. answers. That's a huge mini-split for a bus-sized space, even if it is all metal and glass. I assume this is mostly for AC and not heat, but you could get at least 3, 1-ton heat-pumps (110v.) for the price of a pair of Multiplus, and you might not need 2 of them... why all the extra equipment and complexity?

 

[AdventureBus]

I'm having a hard time seeing why you need so much output, do the windows close?
Looked at the build thread, obviously you're not afraid of engineering solutions, but I don't see the problem that 240v. answers. That's a huge mini-split for a bus-sized space, even if it is all metal and glass. I assume this is mostly for AC and not heat, but you could get at least 3, 1-ton heat-pumps (110v.) for the price of a pair of Multiplus, and you might not need 2 of them... why all the extra equipment and complexity?

Do the windows close? - Yes

Heat will come from bus engine and diesel heaters.

Personal experience with RV usage in hot climates, solidifies in my mind that I will need at least two head units. I don’t want two outdoor units for packaging reasons. Even the smallest dual zone units are split-phase 240V.

This article has some good explanations for RV cooling needs:

What Size Air Conditioner Do I Need for My RV? (Ultimate Guide)

All of our reviews are based on exhaustive research, industry experience, and whenever possible, hands-on testing. When you make a purchase using one of our chosen links we’ll get a small percentage of the proceeds.

www.jeffsetter.com

Keep in mind that this is an all metal bus with lots of windows transporting 9+ people in desert climates as well as visits to sunny south Florida. The cabin is long and narrow and the rear bedroom will be separated by a short hallway. If you still think I can get by with one 120V mini-split, you might need your head checked.

Factory school bus air conditioners can be upwards of 100K BTU! Now thats in an uninsulated bus carrying 65 kids, but still, I don’t think I’m way off base with my thoughts.

I’m considering a 9+24k btu system from Mitsubishi:

Mitsubishi 28,600 BTU 19 SEER Dual Zone Heat Pump System 9+24 - MXZ-3C30NA2 / MSZ-GL09 / MSZ-GL24

The Mitsubishi 19 SEER Dual zone mini ductless split systems are a great choice to ensure that your home is heated and cooled comfortably through the entire year. With their high SEER ratings you will also save plenty of money on your cooling bills.

hvacdirect.com

Dual Multiplus’ in split-phase are common upgrades people make in the RV world. I don’t want to build a system that is lacking for my needs and then have to do it again. I want to build it right the first time.

Now, on to the real reason for my post, does anyone have any technical advice, not just opinions about what I do/don’t need?

 

[AdventureBus]

Fwiw,
I just looked at installation manual for this HVAC thing.
It's not a dual voltage 120-240V appliance.
It's input is 208-240V. It wont need a splitphase power supply.
It might workout better cost wise or efficiency to have dedicated 240V inverter for HVAC, and a 120V inverter for other loads.

Good eye, I had confused that voltage with another unit I was looking at. However, if I’m going to need two inverters anyway for enough capacity, I might as well configure them for split phase in case I need it later. The only difference in wiring the above mini-split is that it will not need a neutral wire, only two hots and a ground.

 

[Alloy]

Are you saying there will be electrical efficiency loss or financial loss?

Financial

The purpose of the 6000w inverter is to pass through the Multiplus inverters. They would be able to tap the house bank to provide PowerAssist and 4800 additional watts of continuous output until the batteries were depleted. I would only need a fraction that capacity for normal use.

Charge the lithium directly.

Consider making the system 48V

https://balmar.net/96-series-48v-alternators/

To run AC for any time 14.4Kw (600Ah@24V) isn't much. Worse is it has to be recharged. Might look at an engine driven compressor.

 

[AdventureBus]

Charge the lithium directly.

Consider making the system 48V

https://balmar.net/96-series-48v-alternators/

To run AC for any time 14.4Kw (600Ah@24V) isn't much. Worse is it has to be recharged. Might look at an engine driven compressor.

Thanks Alloy, I appreciate the suggestions.

I like the thought of charging the LFP batteries directly, but I haven't seen a good way to do so without risking damage to the alternator from load dumping.

I have been thinking about a hybrid battery setup, connecting flooded lead acid to the LFP with a solenoid and BMS.

This guy makes a device and has lots of videos about it: https://www.emilyandclarksadventure.com/bbms

48 volt would be cool and will probably be easy to do in the near future, but the market is still pretty green for those parts in the RV world.

Another alternator I've thought about is the Delco 50DN+: https://www.elreg.com/product/402-8600083-24volt-450amp-50dn-belt-drive-alternator/

Transit buses use those, so you know they have an extreme duty cycle. It puts out a whopping 11,500 watts!

I don't really want the expense of a separate inverter between the starting batts and the Victron inverters, but I think it would be an effective way to create huge output potential with Victron's PowerAssist feature.

I should probably also mention that most of our trips involve long distance driving every few days and I like to park in the shade, so solar isn't my number 1 priority.

 

[AdventureBus]

Here's another layout that would serve my needs. It's less expensive and less complicated. It doesn't provide as many watts of output from the inverters, but it would put less strain on the (bigger) alternator.

 

[AdventureBus]

Here are two more designs that would work for my application. I actually like the dual alternator version (V6) best for fast charging, good packaging, redundancy, and easier on alternators. The 48V version is the least cost-effective way to go about it, mainly due to the need of a 48V bank of series connected 12V lead acid batteries for load dump safety. The components are more expensive and the overall design won't even meet the needs of the mini-split and other loads. The 48V, 100A Balmar alternator puts out approximately 5kW while the dual 24V, 275A Delcos put out 14kW of power. I can buy the two Delcos for the price of one 96 Series Balmar.