If separate charge and load bus, where to connect inverter/charger?

[fxykty]

We have a Victron Energy Quattro, which is a combined inverter and charger. That is, one set of DC cables connect to positive and negative bus bars to provide charging from AC sources to the battery or power from the battery to AC loads. The problem is, if you want to have separate charge and load bus bars, to which bus bar do you connect the inverter/charger DC positive cable? Is it OK to break the 'purity' of either the charge or the load bus? Or, do you need a third positive bus for the inverter/charger connection?

A) If inverter/charger is connected to the charge bus, what happens when you want to disconnect the battery from the charge bus (to absolutely ensure no charging can take place due to high cell voltages) but you still want to have inverter loads (that are being supplied from the charge bus)? Or do you have to live with no AC loads in the case of charge bus cut off? That's OK for all your DC equipment, but what if you run an electric galley, or Starlink, or whatever AC equipment that you don't really want to do without when you dont have to?

B) If inverter/charger is connected to the load bus, what happens when you want all loads disconnected from the battery (due to low cell voltages) but you also want to be able to use AC charging (AC generator or shore power) to get the battery SOC up?

C) If inverter/charger is connected to a separate bus then this will require another disconnect device and duplication of stop charge and stop load relays. Does this increase cost and complexity too much?

D) None of the above, just use a single, combined load and charge bus. If there ever is a disconnection event, I will manually manage the system until it is back to normal.

None of these options is without issues, though the realization that a well-configured and installed system should never get to the disconnect stage for either high or low voltage. With that in mind, which option would you choose?

[sailingunity]

I think D.

My set up is this:

I guess you could say I have a load bus and a charge bus, but my charge bus is connected to the load bus, so it's more of a common. The common is fed from a selector switch, so I can run my house off the start battery if I really have to. Lastly there is an on / off switch right at the battery. I also have an on / off switch to the inverter / charger. I have breakers for all of my solar, wind and start > house charger, so I can kill the charging quickly there if I need to.

If was in a high voltage situation, I would just cut the breakers to the charging sources. You might have your charging sources going through a fuse block, so just pull the fuse (I switched to the breakers because there is no spark and I don't need to go through the app). If plugged into shore power I would also switch the inverter / charger to off.

Low voltage, I would just cut the batteries off at the switch, then evaluate the situation. I might then flip all my DC main panel breakers to off and then switch the battery to on again. If I'm anchored the solar chargers would see the battery and begin charging with no loads.

What you're doing now is good, just have a game plan ready, you might need to tweak some things.

[wholybee]

C. You only need one 3rd relay, and it can be connected to the the other 2 via a diode and gate. Such that if both charge and load are on, the third will also be on.

The problem with D is that if an overvolt condition causes a cutoff, what do you do to manage that? You have no way to discharge the battery. And the reverse is also true, if a low voltage cutoff, you have no way to charge.

By far, preferable would be to not use an inverter charger, but use a separate inverter and charger.

[sailingunity]

Originally Posted by wholybee

C. You only need one 3rd relay, and it can be connected to the the other 2 via a diode and gate. Such that if both charge and load are on, the third will also be on.

The problem with D is that if an overvolt condition causes a cutoff, what do you do to manage that? You have no way to discharge the battery. And the reverse is also true, if a low voltage cutoff, you have no way to charge.

By far, preferable would be to not use an inverter charger, but use a separate inverter and charger.

I explained what I'd do during an overvolt condition - switch off the inverter / charger and charge controllers. No - I wouldn't have 120V, but that's not critical to have on a boat anyway (most of the boat's systems run on 12V). The DC loads would bring the battery charge down.

In an undervolt condition, just go through and flip off the AC and DC loads. Leave everything else on.

I guess if you wanted a completely automated system go the relay route and have a BMS control it. I just don't see the point considering how infrequent someting like that would be.

[PippaB]

The obvious one is don't have a combined inverter/charger....

With the available options I would probably connect to the load bus, since I suspect (guess) big loads from the inverter are more likely to trigger the LVC than charging from the charger is to trigger the HVC. That does leave you without the AC charge, but rebound may give you a connection again once the inverter load is removed.

Or, connect to both through an automatic transfer switch/relay in the positive cable. When shore power is on you are connected to the charge bus, when shore power is off the relay deenergizes and you are connected to the load bus.

[CaptainRivet]

Originally Posted by fxykty

We have a Victron Energy Quattro, which is a combined inverter and charger. That is, one set of DC cables connect to positive and negative bus bars to provide charging from AC sources to the battery or power from the battery to AC loads. The problem is, if you want to have separate charge and load bus bars, to which bus bar do you connect the inverter/charger DC positive cable? Is it OK to break the 'purity' of either the charge or the load bus? Or, do you need a third positive bus for the inverter/charger connection?

A) If inverter/charger is connected to the charge bus, what happens when you want to disconnect the battery from the charge bus (to absolutely ensure no charging can take place due to high cell voltages) but you still want to have inverter loads (that are being supplied from the charge bus)? Or do you have to live with no AC loads in the case of charge bus cut off? That's OK for all your DC equipment, but what if you run an electric galley, or Starlink, or whatever AC equipment that you don't really want to do without when you dont have to?

B) If inverter/charger is connected to the load bus, what happens when you want all loads disconnected from the battery (due to low cell voltages) but you also want to be able to use AC charging (AC generator or shore power) to get the battery SOC up?

C) If inverter/charger is connected to a separate bus then this will require another disconnect device and duplication of stop charge and stop load relays. Does this increase cost and complexity too much?

D) None of the above, just use a single, combined load and charge bus. If there ever is a disconnection event, I will manually manage the system until it is back to normal.

None of these options is without issues, though the realization that a well-configured and installed system should never get to the disconnect stage for either high or low voltage. With that in mind, which option would you choose?

If victron or studer inverter/charger combo the simple answer is c) and you don't need a 3rd and 4th relay for stop load and charge as the remote function of victron and studer works under all conditions to shut off the unit on the DC side. On AC ouput you need a fuse and a RCD. Before the situation arrises that the remote cannot cut the internal fuse blows and disconnects it. Adding additional relays just adds several unnecessary failure points, unwanted voltage drop and costs. On/off with a disconnect switch to be able to manually disconnect you already have anyhow. I connected my c) combo bus without a cut off relay to output of main battery fuse. That's how I have it and approved to be compliant with ISO in europe as mine is certified.

Elegant way of double security would be using trip coil breakers as they catch 3 bunnies at the same time being cable fuse, physical disconnect switch and emergency cutoff by BMS. but for 12V 300 or 400A for multi 12V 3000 I didn't find ones that I would trust to have an equal security to victron/studer remote cut off and been equal in security to an NH fuse. For 150A so 24V or 48V system eg Schneider has a DC trip coil breaker I would trust and that adds security.

[wholybee]

Originally Posted by sailingunity

I explained what I'd do during an overvolt condition - switch off the inverter / charger and charge controllers. No - I wouldn't have 120V, but that's not critical to have on a boat anyway (most of the boat's systems run on 12V). The DC loads would bring the battery charge down.

In an undervolt condition, just go through and flip off the AC and DC loads. Leave everything else on.

I guess if you wanted a completely automated system go the relay route and have a BMS control it. I just don't see the point considering how infrequent someting like that would be.

Under case D, that won't work. And overvolt condition will stop discharge as well. So, the DC loads will all shut off , leaving the boat without power and you with no way to discharge the battery. Only if you also have a way to bypass the BMS and force the relay closed will that work.

Really, the answer is to have a separate inverter and charger. The combined is just the wrong product for this application.

[newhaul]

Originally Posted by wholybee

C. You only need one 3rd relay, and it can be connected to the the other 2 via a diode and gate. Such that if both charge and load are on, the third will also be on.

The problem with D is that if an overvolt condition causes a cutoff, what do you do to manage that? You have no way to discharge the battery. And the reverse is also true, if a low voltage cutoff, you have no way to charge.

By far, preferable would be to not use an inverter charger, but use a separate inverter and charger.

Why only a separate inverter and charger?
I have no issues

Over volt issues won't happen with properly set charger side .
Undervolt won't happen either that's what the solar is for.

A single buss is the best option for 90% of us.in my opinion
KISS

[newhaul]

Originally Posted by fxykty

We have a Victron Energy Quattro, which is a combined inverter and charger. That is, one set of DC cables connect to positive and negative bus bars to provide charging from AC sources to the battery or power from the battery to AC loads. The problem is, if you want to have separate charge and load bus bars, to which bus bar do you connect the inverter/charger DC positive cable? Is it OK to break the 'purity' of either the charge or the load bus? Or, do you need a third positive bus for the inverter/charger connection?

A) If inverter/charger is connected to the charge bus, what happens when you want to disconnect the battery from the charge bus (to absolutely ensure no charging can take place due to high cell voltages) but you still want to have inverter loads (that are being supplied from the charge bus)? Or do you have to live with no AC loads in the case of charge bus cut off? That's OK for all your DC equipment, but what if you run an electric galley, or Starlink, or whatever AC equipment that you don't really want to do without when you dont have to?

B) If inverter/charger is connected to the load bus, what happens when you want all loads disconnected from the battery (due to low cell voltages) but you also want to be able to use AC charging (AC generator or shore power) to get the battery SOC up?

C) If inverter/charger is connected to a separate bus then this will require another disconnect device and duplication of stop charge and stop load relays. Does this increase cost and complexity too much?

D) None of the above, just use a single, combined load and charge bus. If there ever is a disconnection event, I will manually manage the system until it is back to normal.

None of these options is without issues, though the realization that a well-configured and installed system should never get to the disconnect stage for either high or low voltage. With that in mind, which option would you choose?

Honestly the best option in my opinion is D a single buss for charge and discharge. Anything else just creates a point of complexity and failure .
Why make cruising life difficult.

[cram]

I think you're overthinking the wiring ...

You should have an unswitched DC bus for essential loads (radio memory, bilge pump, chargers). The inverter connects to this bus (maybe your alternator as well?). You then have a service disconnect on the DC side of the inverter wiring.

If you have solar power, sending the MPPT outputs to the unswitched DC bus is also a good idea.

From there, wiring goes to the "house battery switch" which power your dc panel, windlass, etc...

To disconnect a battery from the bank, simply remove it's fuse.

So when you leave the boat, you can switch OFF the house switch and you know your battery is still being charged and bilge pumps will also work.

It might be worthwhile to pay for a consult / system design if you've never done this before. https://www.pysystems.ca/resources/diagrams/ there are many companies that offer this remote service.

[CaptainRivet]

Originally Posted by newhaul

Why only a separate inverter and charger?
I have no issues

Over volt issues won't happen with properly set charger side .
Undervolt won't happen either that's what the solar is for.

A single buss is the best option for 90% of us.in my opinion
KISS

The simple answer is if you have a Low frequency inverter or hybrid like Multi or Quattro the charge part is basically for free as its simply the inverter in reverse.
So why pay for a seperate charger if your inverter has a very powerfull one already included. You would pay nearly the amount of the multi to have a charger equal in charge current. That's also why rarely pure charger with high current charge are offered.

Which of his option he is choosing simply depends on the use. I use the combo 98% for inverter purpose and the charger is in 1.9% used via Honda gas gen as charge backup. I basically never plug into shorepower. Main source is solar.
So I treat it as load.
But as explained just C) is the best option and using the remote steering for load and charge, no seperate relays necessary. Simple and KISS.

[newhaul]

Originally Posted by CaptainRivet

The simple answer is if you have a Low frequency inverter or hybrid like Multi or Quattro the charge part is basically for free as its simply the inverter in reverse.
So why pay for a seperate charger if your inverter has a very powerfull one already included. You would pay nearly the amount of the multi to have a charger equal in charge current. That's also why rarely pure charger with high current charge are offered.

Which of his option he is choosing simply depends on the use. I use the combo 98% for inverter purpose and the charger is in 1.9% used via Honda gas gen as charge backup. I basically never plug into shorepower. Main source is solar.
So I treat it as load.
But as explained just C) is the best option and using the remote steering for load and charge, no seperate relays necessary. Simple and KISS.

While I agree to parts of your post
I am actually looking for the opinion reason from wholybee as he was the individual ghat posted concerning having separate inverter and charger.
Myself I run an old school trace 2512 inverter charger as I really like the infinite adjustment of the charge voltage and amperage it provides.

[fxykty]

Thanks everyone so far, it’s interesting discerning the different philosophies that inform the different responses. To add more information on our system, for charge sources we have shore power (very rare), diesel generator, solar panels, wind generator and alternators. For loads we have all the usual DC equipment, an electric galley and lots of AC appliances.

Captain Rivet has provided a good reason to go with option C and not have to add another disconnect relay. Super, can do that with existing equipment. Was leaning towards this anyway.


Regarding complexity, it depends on your system and the environment it’s in. We have extensive electrical usage and battery and charging systems to match. Having more granularity than option D suits our environment (this is our current setup BTW, but we’re about to combine our 2 paralleled 12V LFP batteries into a single 24V battery. This change provides an opportunity to further refine our existing system design.

Why combined inverter/charger? Because separate units would take up more space and weigh more than a combined unit.

Regarding the reply recommending an unswitched DC bus for bilge pumps etc., that’s a great idea but outside the scope of this design question. The disconnect relays (BlueSeas ML-RBS) are right after the main battery fuses and I’m certainly not pulling bolted-in 500A T-class fuses to disconnect my batteries! But I do have a manual switch to disconnect some but not all loads if we’re leaving the boat for an extended time. But as full time liveaboards that’s an interesting question - when do you empty your fridges and freezers?

[sailingharry]

I don't intend to have split bus, as I don't see a real value. But, if you are, I'd put it on either.


* For Charge, set the charger limit to below your HVC -- in theory, it will be shut down on it's own before HVC. Send a copy of the HVC disconnect signal to the inverter to tell it to stop charging (this is needed in case the shutdown is Cell based and not Pack based). In order to have a casualty from this, your charger would need to be smart enough to still charge, but dumb enough to exceed its setpoint and ignore the "stop charging" signal.


* For discharge, set a LV cutoff on the inverter. But this is a bad situation, as the flat curve means that you will be VERY low and about to get a disconnect. Have the BMS send a "shutoff" to the inverter at say 20% (unless you use the inverter for critical loads -- fridge perhaps, 20% is a nice time to shut it down). Have it also send a "shutoff" to inverter, if it is installed on the Charge bus, in parallel to the LVC signal to the load bus contactor.


Note, this requires a BMS able to send signals, and requires an inverter/charger smart enough to have a "disable charge" and "disable invert" external input.


As an aside, I don't agree with the idea of an unswitched critical bus. When the load bus is tripped by the BMS, the battery has well under 1% of energy left. If the first 99% wasn't enough, the last 1% won't make a difference. And trashing the battery in the process means you've got that much more recovery (if there is a recovery to do).

[MatF]

Victron has a bunch of diagrams available, this one suggests they vote with C:

https://www.victronenergy.com/upload...t-and-MPPT.pdf