Connect Solar MPPT to House LFP or Battery Combiner Switch

[Capt.Don]

Hi,
I'm reworking our DC system to support a new LFP house battery. In addition to solar, I'm planning on using a Victron DC-DC 12V/30A charger to charge the LFP battery through the start AGM battery. The alternator and Xantrex XAR regulator will move to the start battery, keeping the current AGM charge profile.

With our old AGMs, I had the Victron solar MPPT controllers connected directly to the house battery. I used a Yandina battery combiner to maintain the start battery. This kept both banks properly charged/floated.

With the LFP battery, I'm debating whether to connect the solar MPPT controllers to the house battery (as with AGMs) or move to the BlueSea battery combiner switch. This gives me the option to switch the solar charge to the house or the start batteries.

During storage (3-4 months), we use a solar panel to float the house and start AGMs. LFP batteries do not require constant float so they can be stored for several months. By wiring the MPPT controllers to the battery combiner, I can switch to the start battery to keep it charged via the solar.

Is this a crazy idea?

I read that the Victron MPPT controllers need to be connected to the battery when solar panels are connected. With the battery combiner switch, it may be possible to disconnect the battery when switching between house/start/both/off. I also have isolation switches on both the house and start, so if either switch is off, there's potentially no path for the solar charge. Is disconnecting the battery a real problem?

If I keep the MPPTs connected to the house battery, should they be connected (1) directly to the battery (as current), (2) after the new house class-t fuse, or (3) after the new battery isolation switch?

Thank you,
Don

[sailingunity]

I have my MPPT controllers on individual breakers, both in and out, so I can break the connection to the solar panels before I cut power to the MPPT.

I have Lithium as well, with the same alternator DC DC charger setup that you have. The positive from my solar goes to the battery combiner switch. I figured if I had a problem with the lithium bank, I could pull the class T fuse on it and set the switch to All, thus charging the start battery from the solar like you're saying (with a slight reprogramming of course)

[Capt.Don]

Originally Posted by sailingunity

I have my MPPT controllers on individual breakers, both in and out, so I can break the connection to the solar panels before I cut power to the MPPT.

I have Lithium as well, with the same alternator DC DC charger setup that you have. The positive from my solar goes to the battery combiner switch. I figured if I had a problem with the lithium bank, I could pull the class T fuse on it and set the switch to All, thus charging the start battery from the solar like you're saying (with a slight reprogramming of course)

Thanks -- and I'm adding an isolation switch after the class T fuse to switch off the LFP.

In the same way, my ancient Heart Freedom charger/inverter is connected to the combiner switch, so it too can be switched between house and start. If we put the boat on shore power, I can switch it over to start, let the DC-DC handle the LFP (or isolate off).

[noelex 77]

Most of the time this will not cause any damage to the MPPT controller, but it can occasionally, so is not good practice.

The other possibility is that the solar controller can be connected to systems (instruments etc) without a battery in the circuit. A great deal of damage can be done to some of these systems. Without a battery to stabilise the voltage the controller will have trouble regulating the voltage to a safe level. High voltage spikes will occur when the controller struggles to regulate the voltage fast enough as the solar conditions change. These spikes can reach voltages where sensitive electronics may be damaged.

It depends on how the system is wired whether or not it is possible to leave the Solar controller suppling power while there is no battery in the system. If this is a possibility, sooner or later it likely to result in an expensive mistake.

[sailingunity]

Originally Posted by noelex 77

Most of the time this will not cause any damage to the MPPT controller, but it can occasionally, so is not good practice.

The other possibility is that the solar controller can be connected to systems (instruments etc) without a battery in the circuit. A great deal of damage can be done to some of these systems. Without a battery to stabilise the voltage the controller will have trouble regulating the voltage to a safe level. High voltage spikes will occur when the controller struggles to regulate the voltage fast enough as the solar conditions change. These spikes can reach voltages where sensitive electronics may be damaged.

It depends on how the system is wired whether or not it is possible to leave the Solar controller suppling power while there is no battery in the system. If this is a possibility, sooner or later it likely to result in an expensive mistake.

That is precisely why I have the solar going to the battery terminal on the combiner switch instead of the common post.

[sailingunity]

Originally Posted by Capt.Don

Thanks -- and I'm adding an isolation switch after the class T fuse to switch off the LFP.

In the same way, my ancient Heart Freedom charger/inverter is connected to the combiner switch, so it too can be switched between house and start. If we put the boat on shore power, I can switch it over to start, let the DC-DC handle the LFP (or isolate off).

I thought about the on / off switch to the bank, but determined it was probably not necessary. If I need to service the bank, I just set the combiner switch to off, and pull the fuse.

[Capt.Don]

Originally Posted by noelex 77

Most of the time this will not cause any damage to the MPPT controller, but it can occasionally, so is not good practice.

The other possibility is that the solar controller can be connected to systems (instruments etc) without a battery in the circuit. A great deal of damage can be done to some of these systems. Without a battery to stabilise the voltage the controller will have trouble regulating the voltage to a safe level. High voltage spikes will occur when the controller struggles to regulate the voltage fast enough as the solar conditions change. These spikes can reach voltages where sensitive electronics may be damaged.

It depends on how the system is wired whether or not it is possible to leave the Solar controller suppling power while there is no battery in the system. If this is a possibility, sooner or later it likely to result in an expensive mistake.

That could be a real problem, especially with the battery isolation switches. I could easily see 20v into the house loads....

[Capt.Don]

Originally Posted by sailingunity

That is precisely why I have the solar going to the battery terminal on the combiner switch instead of the common post.

Right - which is why you sets to 'Both'. Again, if both batteries are isolated off, we are back to the voltage issue on the house loads (instruments).

I can isolate the house loads via the main on/off switch. I'm worried about the inadvertant combination of switches killing the house loads.

[flasher702]

I also have MPPT solar charge controller, 1 house and 1 starter battery banks, and a Victron Orion DC-DC charger between the starter battery and the house battery.

Where my system differs from yours: I have an Epever DuoRacer MPPT dual battery solar charge controller. It connects to both battery banks and charges them independently of each other. Also lets me check the voltage on both battery banks. It's really the ideal solution.

How do you manage turning your DC-DC charger on and off? I have a manual switch. If I ever forget to turn it off I could potentially drain my starter battery. What I want it to do is wait until the starter battery has reached float for a period of time, then charge the house battery, and stop as soon as the starter battery drops even a tiny bit below float (as soon as I turn the engine off, basically). Kinda lame that Victron didn't see fit to give the Orion any smarts beyond max voltage for the small fortune they charge for their stuff...

[Capt.Don]

Originally Posted by flasher702

...How do you manage turning your DC-DC charger on and off? I have a manual switch...

As I understand the Victron DC-DC charges have a smart alternator sense that checks for a change in voltage. I'm hoping this works --or-- the green plug can be used as an on/off switch.

This is one of the after install and how to live with issues I haven't dealt with yet.

[noelex 77]

If the solar controller cannot supply electricity to systems such as marine electronics without a battery in the system that removes most of the risk. However, you did mention in post #1 that you have separate battery isolation switches, and there is still the battery BMS to consider. Check that these cannot inadvertently lead to solar power being directly fed to sensitive electronics without the buffer of a battery, if you want to avoid the magic smoke escaping .

Edit:I see you have considered this in post#7 .

[Capt.Don]

Revising my wiring to move the MPPT to the house battery after the house isolation switch (same connection as house battery combiner). Here's my logic for using the solar to charge the start battery,

1. House loads off while setting switches, so house electronics not connected direct to solar panel
2. House battery isolation switch off (disconnect LFP for long-term storage)
3. Start battery isolation switch on (connect start battery)
4. Solar MPPT charge profile set to AGM
5. As with SailingUnity, battery combiner to Both; this routes solar to the start battery
6. DC-DC should be off due to alternator sense (or wire switch), or no connect output battery

After switches set, can turn on house loads. Solar direct to start AGM; house LFP isolated.

I think this is better -- thanks for everyone's input,
Don

[flasher702]

Originally Posted by Capt.Don

As I understand the Victron DC-DC charges have a smart alternator sense that checks for a change in voltage. I'm hoping this works --or-- the green plug can be used as an on/off switch.

This is one of the after install and how to live with issues I haven't dealt with yet.

Oh, you have the "Orion-Tr Smart" then? It seems I have the Orion-Tr "Stupid"...

[Capt.Don]

I'm not sure if wiring the solar to the LFP house is such a good idea.

If the LFP's BMS shuts down or I disconnect the LFP battery, we then are back to the solar feeding directly the house loads as per post #4. In this case, there's no battery between the solar MPPT and the house loads.

The obvious solution is to connect the solar to the start AGM battery and let the DC-DC charger charge the house LFP.

On a side note, leaving the DC-DC powered without the LFP battery connected appears to draw only .1A.

This is starting to converge! Thanks again,
Don