Apologies for the length, but I wanted to ensure I provide adequate context. I am working on a food truck that will operate all its equipment from a battery-based system. Below, I have outlined the system specifications, the proposed setup, and a few technical questions
System Overview:
We are aiming to run the entire food truck operation electrically, with a 48V / 80kWh battery system, which must be fully charged daily. A 3kW solar array is available, but it alone cannot meet the daily charging requirements, hence the need to integrate a Level 2 EV charger for supplemental charging.
System Components and Configuration:
Battery Configuration:
Five (5) 48V x 16kWh batteries
Each battery lands on a Victron Lynx Distributor, aggregating to power a 15kVA Victron Quattro inverter/charger
The Quattro’s maximum DC input current is 350A @ 48VDC
Charging Source:
A ChargePoint Level 2 EV charger providing 50A @ 220V
Capable of charging the battery system from 10% to 90% in approximately 7 hours
Grounding:
The neutral-to-ground bond will be disabled on the Quattro to allow for external bonding control
Load Requirements:
Max 160A @ 240V
Max 50A @ 120V
Proposed Setup:
Input Side:
The Level 2 charger will supply 50A @ 220V via two hot wires and one ground wire to a J1772 Type 1 Socket Inlet (preferred).
An optional secondary shore power inlet (also 50A @ 220V) may be installed.
Both inlets will exclude a neutral conductor for safety considerations.
An Automatic Transfer Switch (ATS) will manage the switch between shore power and EV charger input.
Output Side:
Each of the Quattro’s AC outputs will connect to a 100A Victron Autotransformer.
Configuration: 2 x 100A @ 220V and 2 x 32A @ 120V
both autotransformers outputs will feed into the main AC breaker panel.
Technical Questions:
Input Side Safety:
Is this input configuration (two hot wires and ground only, without neutral) safe and compliant, particularly with the use of a J1772 inlet and ATS?
Equipment Grounding:
Given the high voltage and current in the system, is it safe and advisable to bond equipment enclosures (such as inverter housings, breaker panels, transformer casings) to the vehicle chassis?
Neutral Bonding Strategy:
Since the grid input does not supply a neutral, and the only neutral exists on the output side of the autotransformers, do I still need to establish a neutral-to-ground bond in the AC breaker panel?
If so, what are the implications of bonding in the panel while the system is charging or in passthrough mode? Is there a risk of back-feeding or ground loop issues?
Autotransformer Isolation:
What is the recommended method to **wire the two autotransformers outputs ** to the AC breaker panel in such a way that, if one transformer shuts down or fails, power from the other transformer does not back-feed into the inactive unit?
Anything metal that contains hazardous AC voltages should be bonded to AC ground.
The real question is, “should AC ground be bonded to the vehicle chassis?”
I would think so, but I’m not an expert on vehicle grounding.
There must always be one and only one neutral-ground bond at all times regardless of power configuration. That can be very challenging to implement with an AT.
The big problem with using an autotransformer is that its neutral must be bonded as well.
But if you mix neutrals, the AT will try to balance shore power (not good).
Or, if there are two N-G bonds while in passthrough, the ground lines will carry objectionable current (very bad). There is no clean way to fix this without switching neutrals, and that is dangerous as well. Autotransformers are fine in fixed static installations, and painful for mobile use where multiple power sources are available.
Thanks Rick. For Equipment Grounding Chatgpt agrees with you. As far as neutral I am not bringing neutral into or out of the truck. I am only planning to wire 3 wires at the truck inlets 2 hot (L1, L2) and a ground. neutral is only created by the autotransformer and bonded once at the AC breaker box.
so at charging or in passthrough mode ? Is there a risk of back-feeding from the truck AC panel back to the building or even worse energizing the ground in the truck?
so far there is a lot of unknows about the autotransformer to breaker connection and it seems that I can’t find info about it so I might need to test system on the ground before putting them in the truck. I have seen professionals on Youtube having dual autotransformers in their food truck system but I can’t find anything to help answer my question, * What is the recommended method to **wire the two autotransformers outputs ** to the AC breaker panel in such a way that, if one transformer shuts down or fails, power from the other transformer does not back-feed into the inactive unit?
I think I found solution for the way to wire the auto transformers. if we are trying to power 220v load there is no reason to even send it to the transformer in the 1st place instead we can send it to a dedicated 220v only breaker panel straight from the quattro using one of the AC out . and we then can use the second AC out from the quattro to go through one auto transformer and create a split phase then a separate breaker for the 120v load and with a bit of load managements that could work. I have 2 * 15A coolers, led lights and a pc. what do you think ??
Hey Rick, I think I found solution for the way to wire the auto transformers. if we are trying to power 220v load there is no reason to even send it to the transformer in the 1st place instead we can send it to a dedicated 220v only breaker panel straight from the quattro using one of the AC out . and we then can use the second AC out from the quattro to go through one auto transformer and create a split phase then a separate breaker for the 120v load and with a bit of load managements that could work. I have 2 * 15A coolers, led lights and a pc. what do you guys think ??
Yes, you can send the 220V straight to a 220v-only panel, but you will need to have a main breaker on it sized appropriately.
Truthfully, the autotransformers do nothing to the 220V loads when connected anyway, other than supply a convenient 100A breaker. But there are some advantages to directly wiring the 220V to a dedicated panel. Your 220V loads will still work fine if the AT fails or its breaker trips. This panel must be properly labeled “220V only” because if someone later thinks ground is neutral and can put in a 120V breaker, the current will go through the ground wire.
Even though you have not included a neutral on the input side, that neutral is still bonded to the ground line at the source of shore power presumably. If you bond the autotransformer neutral to ground in the 120v panel, you have effectively connected the AT neutral and the shore power neutral through the ground wiring. Objectionable current will flow through the ground line. Frustrating, isn’t it?
If you don’t bond the autotransformer neutral to the panel, then you have a safety issue when not running on shore power. I guess I would use the ground relay in the AT as it is designed for this case when running from inverter only, and not hardwire bond the neutral to ground in the 120v panel.
This solution does not address the potential mismatch of voltage between the AT neutral and the ground when running in shore power mode, and I’m not sure if that will be a hazard or not.
I have no experience with two ATs in the same system, so I can’t comment there. In principle, they can be wired in parallel to increase available neutral current.
Hi Rick, thanks for the Validation, I was hopping that the AT has a ground relay setting like the one in the inverter but I couldn’t confirm it because it’s not mentioned anywhere. I know that victron has documentation for the settings parameters for it’s hardware. But I can’t seem to find one for the AT. Thanks again.
The Victron Autotransformer has a ground relay that can automatically switch using the external ground relay function of a multiplus or quattro, so that part is easy. You enable the ground relay on the quattro but set a DIP switch to send 24V over to the AT. You need to run a pair of low-voltage wires. The relay in the Quattro is not activated. The AT itself has no firmware or software settings.
That’s perfect. Thanks for the explanation. Now question, is the AT limited to 32A of split phase or it’s 32A of imbalanced split phase load? my 120v load is 2 coolers peak at 15A, water pump, lights and 2 PCs registers. If I put the coolers on separate legs to balance the load will that be ok or I am going to over heat the AT??
The autotransformer limitation is on neutral current, which is caused by imbalance on the L1 and L2 lines. The limitation is 28A continuously, and 32A maximum. The breaker trips based on temperature of the coil. Both the 32A and 100A models have the identical limitation because they use the same coil. The 100A version simply allows more 240V loads to be used through its breaker.
Balancing the coolers on separate legs is the way to go. Heat generated is proportional to the neutral current. If both coolers are identical and active, the neutral current will be near 0A. 120V * 28A is 3360 VA, so watch out for single loads that approach that wattage being the only thing running.
" This solution does not address the potential mismatch of voltage between the AT neutral and the ground when running in shore power mode, and I’m not sure if that will be a hazard or not." I am not worried about shore power pedestals because you can easily test power pedestals before plugging in however I can’t say the same about the public level 2 EV chargers, that’s going to be figured out later I guess.
" I do own two Victron autotransformers, and they generally get lots of questions here."
You know a lot about this subject I truly thought you work for Victron, lol
** follow up, I found out that the Victron Quattro 2nd AC out is only available when connected to the grid So I setup all the AC output to go to a 200Amp 230V only Breaker panel to power all my 230V load and then I also added a 50Amp breaker to feed the autotransformer 230 AC in. I was able then to step that down to 2* 110V lines going to a 100 Amps 110 V sub-panel. and for safety I am also going to use all GFCI breakers as well. I am also going to bond ground and Neutral in the transformer only when I am not in the pass through mode using the relay in the quattro.