Solar panels, alternator; charging separate banks

[sailoppopotamus]

Current setup:
- A house battery (AGM 2x150Ah, 12V, in parallel) and an engine/windlass 80Ah battery (VRLA, non-AGM, possibly due for replacement).
- 2x100W 12V panels in parallel
- A single-output Victron PWM controller
- A Sterling 2-output mains charger
- A Victron Argodiode

The PWM controller charges the house batteries. The alternator (stock Yanmar 2GM20F) goes to the Argodiode, which is connected to the two batteries. The current setup is sub-optimal because the engine/windlass battery is chronically undercharged (due to diode voltage drop, not running the engine for long enough to replenish charge lost in starting it and weighing anchor, and when the boat stays on the hard for months away from a battery charger).

I would like to improve the setup so that the engine/windlass battery is also charged from the solar panels. I would also like to upgrade to an MPPT controller. My options from cheapest to most expensive look like:

1. Connect the MPPT controller to a Victron Cyrix combiner, which is then connected to the two batteries.
2. Connect the MPPT controller to a Victron Argofet VSR, which is then connected to the two batteries.
3. Connect the MPPT controller to the house battery, then a Xantrex Echo Charger to the starter battery.

Is there any reason why I wouldn't go for the first option? I realize that (1) and (2) require similar battery chemistries, so I'll have to swap out the engine/windlass battery for an AGM one if I go down this route. Will I have to modify the alternator wiring in any way? Also, this might be a stupid question, but can I remove the Argodiode entirely and connect solar and alternator to the same Cyrix combiner, or is that likely to cause problems?

I would be grateful for any feedback/help with this.

 

[Tranona]

Not a good idea to run the windlass off the engine start. Engine battery should be just that (with a means of using the house bank in an emergency). It will always be charged immediately after start. Replace the diode with a VSR would be a good move all round. Rewire the windlass to use the house bank or even consider a dedicated bow battery charged by a B2B from the start, although as you have the wiring back to near the house probably best to stick with that. No real need to connect the solar to the start and you can use one of the outputs for the mains charger for the winter.

If you are replacing the start battery consider a high output AGM such as commonly used for stop start cars. A 65Ah would be fine. If you have a long time horizon and deep pockets then a Red Flash or Odyssey is even better. Half the size and weight, can be mounted in any orientation and lasts - the Red Flash in my Morgan lasted 19 years!

 

[geem]

I would go for the Victron B2B to charge the engine battery off the solar via the house bank.
Nothing wrong with the windlass coming from the engine battery since the alternator charges the engine battery.
If you ever opt for lithium house batteries the windlass from the starter battery is the way to go as well. Inrush currents of large DC motors cannot be easily tolerated by a lithium house battery BMS.

 

[William_H]

I would think windlass running off engine battery would be right assuming you always have engine running when operating windlass. Because charge from alternator should go direct to windlass. However not so if you have a diode fitted between alternator and engine battery.
If the Argo diode is indeed dropping .7volt of charge voltage (not compensated by battery voltage sensing or regulator) then it should be replaced by FET type diode splitter or VSR. to give full charge from engine.
However I think the simplest way to keep engine battery topped up is with another (small) solar panel. With or without a regulator. 10w OK without regulator.
Or divide solar panels and have one for engine battery with cheap regulator. (use PWM reg for engine battery and buy a new MPPT for service battery.)
ol'will

 

[Baggywrinkle]

IMO .. E-bay the Argodiode, fit a victron battery combiner between the house and starter banks. It will close if a charging voltage is seen on either side of the combiner allowing both battery banks to charge from either solar or alternator.

It also supports a switch to close it for 30 secs to force it to close if you need to use the house batteries to start the engine. (wiring must be of appropriate size)

Cyrix Battery Combiners - Victron Energy

My system looked like this ....

 

[chris-s]

Or, sell all those bits and replace with a Renogy Onboard MPPT DC-DC charger. This will use both alternator and solar to keep both battery sets charged whilst keeping the battery sets separate. Just another option.

 

[Trident]

You can solve this very simply. Keep solar on to the house battery only and get an MPPT to improve charging. Also look at whether putting the panels in series might help in your case - it will depend on where they are, what shadows them etc but my give more power in the morning and evening when the sun is weaker .

Put a VSR between house and engine bank and this will charge the start from the solar when the sun is shining. No need to but expensive parts - Durite etc do very good 120A VSRs for £40. Take off all the other stuff between alternator and battery.

Total cost about £50 to get the VSR with fuses and £80 for an MPPT like the Renogy version which is very good

The MPPT DC DC from Renogy recommend above is also very good and does the job of solar regulation and DCDC between battery banks with charge profiles you can set to match the battery type and is only £100 more

Finally take the opportunity to check all your wiring and connections are good and tight while doing it

 

[sailoppopotamus]

Not a good idea to run the windlass off the engine start.

Nothing wrong with the windlass coming from the engine battery since the alternator charges the engine battery.

I would think windlass running off engine battery would be right assuming you always have engine running when operating windlass.

I don't have a strong preference for the current setup, which came with the boat. Without wanting to be dismissive of @Tranona's input, which I'm grateful for, this has been discussed several times on the forum so I'd prefer if this dilemma didn't derail this thread. From what I understand a large reason for separating house & start batteries is to ensure that you can always start the engine, even if your fridge/lights/electronics ran down the battery. I don't see how this could happen with the windlass. Either way, a dedicated windlass battery is a no-go for my 30ft boat that already carries more than 100kg in batteries.

However I think the simplest way to keep engine battery topped up is with another (small) solar panel. With or without a regulator. 10w OK without regulator.
Or divide solar panels and have one for engine battery with cheap regulator. (use PWM reg for engine battery and buy a new MPPT for service battery.)
ol'will

Aside from the practical difficulties of mounting yet another panel, this seems like an inefficient setup. I would like to use all charge available (solar, or alternator) to charge whichever battery needs it. Partitioning charging like you suggest might lead to scenarios where the engine battery is not fully charged and my 200W panels are not being used to charge it.

@Baggywrinkle thanks, the diagram is very useful.

It seems that it comes down to the question of a battery combiner or a DCDC charger. As far as I can tell, in my scenario the only practical difference between these options apart from price is that a DCDC charger will actually keep the banks completely separate, whereas the combiner will put them in parallel whenever the sun is shining. So if I start the engine or use the windlass during the day, I'll actually be using the house *and* start batteries to do this. Whether this is a good or a bad thing I'm not sure.

Unfortunately the Renogy product is not available locally -- I could of course order off the internet but I'm trying to get this sorted as soon as possible and go sailing.

 

[sailoppopotamus]

One more, potentially stupid question. The typical scenario in my application will be a mostly full starter battery, and a house battery that has been running the fridge all night and is in a deeper state of discharge. The sun comes out, the VSR/combiner closes, and the two batteries are now in parallel (and charging off the solar panels). Doesn't this mean that there will be an 'unregulated' current flowing from start to house? Isn't this similar to me just having two batteries at different SOC on a workbench, and just putting them in parallel to charge one from the other? Which I imagine is a very sub-optimal way of charging.

 

[sailoppopotamus]

One more, potentially stupid question. The typical scenario in my application will be a mostly full starter battery, and a house battery that has been running the fridge all night and is in a deeper state of discharge. The sun comes out, the VSR/combiner closes, and the two batteries are now in parallel (and charging off the solar panels). Doesn't this mean that there will be an 'unregulated' current flowing from start to house? Isn't this similar to me just having two batteries at different SOC on a workbench, and just putting them in parallel to charge one from the other? Which I imagine is a very sub-optimal way of charging.

To answer my own question, it looks like this is the difference between a battery isolator combiner (Cyrix) and a VSR (Argofet), in that the former will not allow current to flow from one battery to another. If a more knowledgeable person knows better please correct me.

 

[Tranona]

My reason for suggesting you run the windlass off the house bank is because you specifically stated that the start battery does not get recharged after use. Part of this is solved by changing the diode for a VSR, but the house bank is much more suitable (300Ah capacity!) for running the windlass as not only do you have the charge from the alternator, but also from the solar. I agree about not changing to a dedicated windlass battery as you already have the cables in place. £50 for the VSR and perhaps a little bit of cabling to run the windlass from the house. Then you can go for a smaller start battery which is quickly recharged from the engine, has a low rate of self discharge and can be charged from mains if necessary.

 

[PaulGooch]

To answer my own question, it looks like this is the difference between a battery isolator (Cyrix) and a VSR (Argofet), in that the former will not allow current to flow from one battery to another. If a more knowledgeable person knows better please correct me.

The Cyrix is a VSR.

 

[PaulGooch]

My reason for suggesting you run the windlass off the house bank is because you specifically stated that the start battery does not get recharged after use. Part of this is solved by changing the diode for a VSR, but the house bank is much more suitable (300Ah capacity!) for running the windlass as not only do you have the charge from the alternator, but also from the solar. I agree about not changing to a dedicated windlass battery as you already have the cables in place. £50 for the VSR and perhaps a little bit of cabling to run the windlass from the house. Then you can go for a smaller start battery which is quickly recharged from the engine, has a low rate of self discharge and can be charged from mains if necessary.

If the solar is charging the engine battery, it will get charged.

Using the windlass from what could be a depleted domestic bank could play havoc with sensitive electronics.

 

[sailoppopotamus]

The Cyrix is a VSR.

You are right. I understand that it's a VSR deep down, my phrasing wasn't very good. I was attempting to clarify the difference between the Argofet and Cyrix products.

 

[geem]

One more, potentially stupid question. The typical scenario in my application will be a mostly full starter battery, and a house battery that has been running the fridge all night and is in a deeper state of discharge. The sun comes out, the VSR/combiner closes, and the two batteries are now in parallel (and charging off the solar panels). Doesn't this mean that there will be an 'unregulated' current flowing from start to house? Isn't this similar to me just having two batteries at different SOC on a workbench, and just putting them in parallel to charge one from the other? Which I imagine is a very sub-optimal way of charging.

I don't like the VSR for this reason. A fully charged engine battery gets more charge and voltage than it needs when combined with a depleted house battery. Instesd, the B2B keeps the engine battery in isolation and charged on a proper 3 stage charge profile. A far better way for long battery life. You can also set the battery manufacturers specific voltage requirements for that battery

 

[sailoppopotamus]

To answer my own question, it looks like this is the difference between a battery isolator combiner (Cyrix) and a VSR (Argofet), in that the former will not allow current to flow from one battery to another. If a more knowledgeable person knows better please correct me.

Turns out this was just wrong. If anything it seems like the opposite is true -- the Cyrix will allow current to flow between the batteries, whereas the Argofet maintains the electrical isolation of the two batteries. It would seem Argofet is the way to go then, but you can't really put an MPPT on its input side precisely because there won't be any power to the MPPT from the battery when there is no solar. So the Argofet is not the solution to my problem.

 

[Baggywrinkle]

One more, potentially stupid question. The typical scenario in my application will be a mostly full starter battery, and a house battery that has been running the fridge all night and is in a deeper state of discharge. The sun comes out, the VSR/combiner closes, and the two batteries are now in parallel (and charging off the solar panels). Doesn't this mean that there will be an 'unregulated' current flowing from start to house? Isn't this similar to me just having two batteries at different SOC on a workbench, and just putting them in parallel to charge one from the other? Which I imagine is a very sub-optimal way of charging.

The battery combiner has a microprocessor in it which monitors the voltage on both sides of the combiner. It will not close if there is no charging source present .... this means there will be no "leakage" from a charged starter to a discharged house bank for example as the close voltage is above that which a battery alone provides.

The logic in the combiner is also such that if the combiner is closed due to solar charging, and you attempt an engine start, then unless you have a huge amount of solar, capable of keeping the house bank voltage above float during engine cranking, then the combiner will immediately disengage, and the starter current will only be drawn from the starter battery.

The combiner is not really doing anything different to the argodiode (apart from the fact if has no voltage drop) ... the argodiode charges both house and starter in parallel from the alternator, but prevents the solar from charging the starter and isolates the battery banks from each other.

Think of the battery combiner as a smart isolator, which allows charge in both directions, but prevents flow of current between the battery banks when no charging source is active (alternator or solar). It also has the benefit of allowing an engine start from the house batteries at the push of a button if the starter battery dies for example.

When combined and charging form solar, you will find that the combiner only closes when the house batteries approach the charge level of the starter, so the scenario where the house batteries deplete the starter does not in practice happen. I never saw this on my boat.

@geem is correct in that a good DC-DC Charger will charge the batteries more effectively as it will have a proper charging profile which an alternator doesn't. Something like a Sterling Alternator To Battery Charger will look after both starter and house banks - but it won't give a "push button" combine function in emergencies.

IMO, having run a lead acid system (not AGM) with a battery combiner for a number of years I can testify that it worked superbly, I didn't have problems with either battery bank while I had the boat.

It's a question of budget, what your own priorities are, and if you want to invest now to enable a later Lithium install. A combiner is only useful between battery banks of same technology batteries.

Have a quick read of the Cyrix manual ... https://www.victronenergy.com/upload/documents/Manual-Cyrix-ct-230-EN-NL-FR-ES-DE-.pdf

 

[Baggywrinkle]

Turns out this was just wrong. If anything it seems like the opposite is true -- the Cyrix will allow current to flow between the batteries, whereas the Argofet maintains the electrical isolation of the two batteries. It would seem Argofet is the way to go then, but you can't really put an MPPT on its input side precisely because there won't be any power to the MPPT from the battery when there is no solar. So the Argofet is not the solution to my problem.

Did this in my camper van using an Argofet to overcome this exact problem .... it works

The bigger Argofets have an "energise" option to provide 12v to energise an alternator. You can use this to energise the MPPT too.

 

[PaulGooch]

Turns out this was just wrong. If anything it seems like the opposite is true -- the Cyrix will allow current to flow between the batteries, whereas the Argofet maintains the electrical isolation of the two batteries. It would seem Argofet is the way to go then, but you can't really put an MPPT on its input side precisely because there won't be any power to the MPPT from the battery when there is no solar. So the Argofet is not the solution to my problem.

The ArgoFET is a modern, FET based device that would directly replace your ArgoDiode, but without the voltage drop. So it solves the voltage drop issue, but does not give the ability to charge the engine battery from solar. Victron do not support connecting the solar controller to an ArgoFET, the solar controller should be connected directly to the batteries.

The Victron Cyrix is a micro-processor controlled VSR, i wouldn't use cheap VSRs. You could connect the alternator output directly to the engine battery and the solar controller to the domestic bank and fit a Cyrix between the two banks. This is a common solution, fitted to millions of boats. A Cyrix will cost you just over £40, plus a bit of wire and a fuse or two.

Another alternative is the previously mentioned battery to battery charger. With this, you'd connect all charging sources to the domestic back, then use the BtoB to charge the engine battery. A 30a Victron B2B will set you back about £260, plus wiring etc.

 

[PaulGooch]

The battery combiner has a microprocessor in it which monitors the voltage on both sides of the combiner. It will not close if there is no charging source present .... this means there will be no "leakage" from a charged starter to a discharged house bank for example as the close voltage is above that which a battery alone provides.

The logic in the combiner is also such that if the combiner is closed due to solar charging, and you attempt an engine start, then unless you have a huge amount of solar, capable of keeping the house bank voltage above float during engine cranking, then the combiner will immediately disengage, and the starter current will only be drawn from the starter battery.

This not not quite right, the Cyrix will not immediately open, there will be a delay, based on battery voltages etc.

When combined and charging form solar, you will find that the combiner only closes when the house batteries approach the charge level of the starter, so the scenario where the house batteries deplete the starter does not in practice happen. I never saw this on my boat.

The combiner will close when the voltage at either battery reaches the set point for closing, the voltage of the other battery is not relevant. If the domestic battery was fairly depleted and the solar input was high enough to close the VSR the terminal voltage of the domestic battery would be higher than that of the engine battery and no current would flow from the engine battery to the domestics. So you are correct that the domestic won't drain the engine battery.

@geem is correct in that a good DC-DC Charger will charge the batteries more effectively as it will have a proper charging profile which an alternator doesn't. Something like a Sterling Alternator To Battery Charger will look after both starter and house banks - but it won't give a "push button" combine function in emergencies.

IMO, having run a lead acid system (not AGM) with a battery combiner for a number of years I can testify that it worked superbly, I didn't have problems with either battery bank while I had the boat.

It's a question of budget, what your own priorities are, and if you want to invest now to enable a later Lithium install. A combiner is only useful between battery banks of same technology batteries.

Have a quick read of the Cyrix manual ... https://www.victronenergy.com/upload/documents/Manual-Cyrix-ct-230-EN-NL-FR-ES-DE-.pdf