geem
Well-known member
Since the B2B will charge 24/7 from the domestic battery if you want it to, you only need a low current version. A 10A unit is about £120.
I have three installed in this way, keeping battery on float 24/7
Solar panels, alternator; charging separate banks
- Thread starter sailoppopotamus
- Start date
I have three installed in this way, keeping battery on float 24/7
Buck Turgidson
Well-known member
I have a Cyrix which does what it says on the tin but I think it may have an intrinsic fault that had me scratching my head for a bit.
With solar charging the house side the batteries are connected whether you like it or not. You effectively start the engine off both batteries. This will hide a latent fault in your starter battery unless you occasionally either start your engine at night or disconnect the house battery or the sensing wire from the cyrix to ensure it’s open. I’m thinking about fitting a switch in the sensing wire so I can manually disconnect it to start. However, there is a timer built in so it doesn’t disconnect immediately.
I’m still thinking about a solution.
With solar charging the house side the batteries are connected whether you like it or not. You effectively start the engine off both batteries. This will hide a latent fault in your starter battery unless you occasionally either start your engine at night or disconnect the house battery or the sensing wire from the cyrix to ensure it’s open. I’m thinking about fitting a switch in the sensing wire so I can manually disconnect it to start. However, there is a timer built in so it doesn’t disconnect immediately.
I’m still thinking about a solution.
sailoppopotamus
Active member
Thanks for the detailed post. I wasn't concerned about flows when no source is active or when starting. The part that is unclear to me is how currents flow when a charging source is present but with the two batteries in a very different state of charge. One might require bulk absorption charging, the other might require just a float charge, but the Cyrix will put them in parallel. How does each one charge?
@Baggywrinkle chimes in with another excellent diagram. However I just realized that a small Argofet and the Orion 12-12/18A charger cost a similar amount of money. Still more than the Cyrix, but not absurdly so. I was therefore leaning towards the following setup:
Sidestepping the question of the windlass connection, this would seem to do what I want, I think. I connect the alternator directly to the house battery without the Argodiode's voltage drop, and do the same for the solar controller. If the start battery craps out I can presumably hot wire the two batteries without damaging the Orion charger. Does anybody see any issues with this setup, or disadvantages relative to a battery combiner based setup?
PaulGooch
Active member
That works fine for charging. You CANNOT use the emergency start switch unless you disconnect the BtoB
Baggywrinkle
Well-known member
Depending on the state of charge of the battery, the MPPT would most likely start in the morning by bulk charging (mine does) .... the empty house batteries will then draw current dependent on their internal resistance - the emptier they are, the more current they draw. This pulls the charge voltage down ... so during bulk charging, the voltage won't be enough to close the Cyrix.
As the batteries become fuller, they accept less current and the voltage climbs, until at some point the charger switches to absorption ... during this phase, the Cyrix will see the voltage rise to above the level where it will combine the house and starter banks. It will then close and the starter bank will be connected. The voltages and logic can be seen in the manual I linked to in a previous post.
If the starter is discharged, it will draw current and pull the voltage down, the MPPT will respond by re-entering bulk mode and will provide more amps (given enough sun). The starter will then be bulk charged and current will be flowing to all batteries dependent on their internal resistance (their need).
At some point the starter will also enter absorption, and eventually all batteries will end up on float.
If however, there are loads present because the boat is in use, (fridges, inverters etc.) then the MPPT will remain in bulk for most of the day as it can't tell the difference between a battery drawing charge current and a normal load like a fridge or an inverter. This is why it is not really worth getting hung up on bulk, absorption, float when the boat is in use, your shore power charger will also act as a power supply if the boat is in use - Charge profiles are really important when all the loads are disconnected and the solar is running to prevent self-discharge of the batteries, or you have an unused boat permanently on shore-power.
This Cyrix behaviour prioritises the battery bank to which the charge source is attached - with the Cyrix connect only happening once the charging battery bank has reached a high enough voltage (a high enough charge state).
Normally the alternator is attached to the starter bank, and the solar to the house bank. The combiner then allows cross-charging to the secondary bank once the bank with the charge source has reached a set voltage. Makes sense, after an engine start, you want the starter battery prioritised, and with solar, the house batteries - especially when the boat is in use.
In your diagram, the alternator should be on the starter side IMO, and I personally would drop the B2B and put a Cyrix between the banks with the emergency start option.
B2Bs really come into their own when you have either different voltages for house and starter (e.g. 24V / 12V) or different technologies Lead/Lithium which require different charging strategies.
The are particularly important in Lithium house battery installs to prevent the Lithium batteries from burning out the alternator.
Baggywrinkle
Well-known member
A typical engine start will pull the battery voltage well below 12V, and often below 10V dependent on the engine/glowplugs etc ...
The Cyrix spec for connect/disconnect is here:
A drop below 11V will disconnect the Cyrix immediately.
A typical battery voltage curve during engine cranking looks like this ... (Start is at 1 sec)
This curve would immediately disconnect the Cyrix. After 2 secs, the alternator starts charging and the voltage rises ... the Cyrix will reconnect again in 4 secs -5 mins dependent on voltage.
The Cyrix spec for connect/disconnect is here:
A drop below 11V will disconnect the Cyrix immediately.
A typical battery voltage curve during engine cranking looks like this ... (Start is at 1 sec)
This curve would immediately disconnect the Cyrix. After 2 secs, the alternator starts charging and the voltage rises ... the Cyrix will reconnect again in 4 secs -5 mins dependent on voltage.
Buck Turgidson
Well-known member
Unfortunately mine doesn’t do that. If the batteries are connected when I start the engine my odyssey PC1800 doesn’t flinch and the battery voltage felt on both sides of the cyrix remains the same.
Baggywrinkle
Well-known member
What is the engine that the PC1800 is starting?
geem
Well-known member
I would argue that a B2B is a far more satisfactory solution. Given enough solar and domestic battery capacity, the engine battery can be kept permanently on float from the domestic battery via a B2B. No cycling or over charging due to being connected via a VSR to a depleted house battery. The engine battery can be kept in tip top condition.
Buck Turgidson
Well-known member
2qm15. It’s my house battery. Start is a 60ah Agm
Baggywrinkle
Well-known member
I don't know, engine alternator to the house batteries instead of the starter just seems wrong. Failure of the B2B or problems with the house bank will mean the starter battery may not charge at all, instead it will discharge while the engine is running as the engine electrics run from the starter battery, including the glow plugs. It simply increases the number of possible points of failure that could put the engine out of action.
A dead starter battery will also mean jump-leads or a re-wiring exercise to start the engine from the house bank, or bypassing the B2B and shorting its input to its output with heavy-duty wiring and a switch.
When the engine is not running, the solar MPPT will be attempting to complete bulk, absorption and float cycles on the house bank, while the B2B, being fed by the MPPT, will be attempting it's own bulk, absorption, float cycle on the starter battery - the fluctuating voltage of the MPPT (due to cloud cover, shading) will be interpreted by the B2B as engine run/off, messing up it's charging cycles, this can be disabled, but then it will just be a parasitic load on the house bank until the MPPT kicks in, or the house voltage drops below the cut-off voltage. A B2B is only around 87% efficient so 13% of the energy is also wasted.
IMO a B2B definitely has a place in mixed chemistry battery banks, and it is also the go to solution for creating a proper charge profile for a battery that would normally be charged by an alternator - and most importantly, preventing an alternator from being burned out charging a Lithium bank.
To my mind, the Cyrix is a neat solution to the problem of multiple charge sources while keeping the engine electrical system and the house electrical system isolated and independent from each other in a setup where the battery chemistries are all lead acid. The added bonus of an emergency start button allowing starting from the house bank is a neat extra.
If you have a massive house bank, with a BMS controlling discharge so the house bank can never be damaged by the B2B load then this is a different story - but with a lead acid house bank, and no battery protection, the parasitic load could well be a disaster depending on the depth of discharge before the B2B shuts off - although I would seriously consider a trickle charger instead of any of the Victron B2B chargers as the smallest Orion-Tr Smart is 18A
geem
Well-known member
That's not how you do it.
The .B2B charging the engine battery is on permanent float once it is charged. The load on the house battery is maybe 5w to stop self discharge. It can sit like this 24/7 with a full charge every few weeks, initiated be a flick of a switch if you want. There is no conflict for MPPT. It just charges the house bank.
Engine and house bank emergency arrangement can be set up how you like. A switch to join them or a switch to send alternator charge to house in an emergency. Lots of ways to do that. Having the alternator charge the house bank means lots of charge to the battery that is most likely to need it. A far better arrangement. You just need to get used to using new tech and doing thing differently now that it is available.
Whist the boat is sat on a mooring or in a marina for days on end, the house bank gets a perfect three stage charge and the engine battery does the same through the B2B. What can be better than that for battery life
Baggywrinkle
Well-known member
OK ... where to start. When charging, engine stopped, where is the Starter B2B getting it's power from? Answer, the house bank, which is currently in either "not being charged" (night time) or in bulk, absorption or float from the MPPT dependent on available light and the charge cycle algorithm. If you're on the boat, and the sun is shining, then the MPPT will most likely be in bulk, not necessarily because the batteries need it, but because of the house loads. So you will have a MPPT in bulk charge mode, feeding house loads and a B2B to the starter. Don't know about your MPPT but mine switches back and forth between bulk, absorption and float all day dependent on the house loads and the available sunshine.
The B2B (at least a Victron-Tr Smart) has an engine on detection algorithm .... there is a clue as to why Victron chose to call it an engine on detection algorithm, it was conceived to allow current limiting and 3 stage charging from an alternator (with attached starter) to a house bank when there is a charge source present. The intended application can be seen in the diagram below, and here is a bit of info from their manual ...
Your MPPT for all intents and purposes looks like a smart alternator to the B2B, providing variable voltage at the B2B inputs so the B2B will be cycling on and off charging the starter battery. Dependent on how the charge algorithm is set up it may well start another charge cycle. You can turn this detection off, but then you produce a permanent parasitic load on the house bank, and a damaged starter will be able to deplete the house bank as they are no longer isolated. Setting the cut-off voltage to the float voltage of the MPPT will limit this, but but a B2B is only 87% efficient in the power it does transfer to it's output.
Why introduce a B2B and the complexity when you don't need to? and as for regulating everything with switches, IMO, a fit and forget solution wins every time.
As a second point, if using a B2B, then I fail to see why you would want to connect the alternator, which doesn't have a multi-stage charging algorithm, to the more expensive house bank and run a B2B to the starter instead of the other way round. I personally would wire it exactly as shown in the Victron diagram if I were to be using a B2B charger in a lead acid setup - or are you suggesting Alternator -> 1st B2B -> House -> 2nd B2B -> starter? 2 B2Bs in a lead acid system instead of a Cyrix?
But back to the original problem the OP had, which was to enable trickle charging of the starter from the MPPT which is connected to the house bank.
IMO, 1st option,
A Cyrix provides an emergency start out of the box. It allows charging in both directions, from alternator/starter to house and from MPPT/house to Starter ... it keeps both banks isolated from each other unless a charging source is present on either side of the Cyrix. Disadvantage is it charges the house bank from the alternator without a multi-stage charge algorithm, but from the MPPT both battery banks are in parallel and will both get a 3-stage charge from the MPPT. My boat ran like this with lead acid batteries for around 3 years with no sign of deterioration of either of the battery banks - I would not hesitate to wire another lead acid system the same way ... and the house bank was very effectively charged from the alternator as the starter was pretty much always full, so even though it was prioritised during alternator charging, the Cyrix closed quickly and the house batteries were being charged within a minute or so of the engine starting.
2nd option,
An Argofet, could be used to replace the Argodiode to remove the diode voltage drop, then the energise terminal could be used to provide 12V at the input. The MPPT can then be connected at the same Argofet Input as the alternator ... both MPPT and Alternator would then charge both banks and they would remain isolated. This is the setup I have in my VW Bus and it works superbly - again, all lead acid and no B2Bs. Disadvantage is no emergency start option out of the box.
3rd option,
Hang a trickle charger off the load output of the MPPT to charge the starter battery, so when the MPPT is producing power, the starter is charging - another good solution as the banks remain isolated and the starter battery is only being charged by solar, and not depleting the house bank. Both banks get independent and appropriate charging. No emergency start out of the box.
Or there is the 4th option which @geem seems to favour,
Connect a B2B between the house bank and the starter, run both the alternator and the MPPT to the house bank. Advantage, both banks get independent 3-stage charging from solar, disadvantage - 87% efficient B2B, engine panel charge light no longer indicates that the starter is actually being charged, and the wierd bit, the more expensive house bank doesn't get a 3 stage charge from the alternator, but the cheaper starter does - even though there is a B2B fitted.
Then there is option 3B where 2 B2Bs are fitted, one for the house bank and one for the starter?
IMO connecting the alternator to the house bank, and charging the starter using a B2B is pretty weird, even if only because the charge light on the engine panel no longer indicates that the starter battery is being charged .. and the OP has a lead acid system and much lower available house capacity.
Anyway .. some useful resources ...
Use of an Argofet in a lead acid system ...
https://www.victronenergy.com/uploa...h-BMV-Cerbo-GX-Touch-50-Argo-Fet-and-MPPT.pdf
Use of a Cyrix combiner in a lead acid system ....
https://www.victronenergy.com/upload/documents/13--CYRIX.pdf
https://www.victronenergy.com/upload/documents/Manual-Cyrix-ct-230-EN-NL-FR-ES-DE-.pdf
Use of an Orion-Tr Smart in a lead acid system ... the only example in the Victron library of an Orion-Tr Smart charging lead acid batteries is a bow thruster battery on a canal barge. In every other case they are being used between an alternator (connected to a lead acid starter) and a lithium house bank.
https://www.victronenergy.com/uploa...X-touch-50-Bow-thruster-Galvanic-isolator.pdf
The complete library of Victron schematics can be found here, covering off-grid systems, vans, boats etc. ....
System schematics - Victron Energy
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geem
Well-known member
Many liveaboards with large house banks charge their house banks with their alternator because it will put lots of amps in quickly. Far more efficient than a B2B in most cases. Many liveaboard install large banks and high output alternators for this reason. To keep the engine battery charged, a B2B is a simple easy, to do, solution. Not complicated. The status of the engine battery is available on your phone via Bluetooth. In addition, a voltmeter on the panel will tell you SOC or certainly if something is wrong.
Topping off the batteries then with solar and MPPT works well, but the heavy lifting is done with the alternator. The system ensures optimum engine starter battery condition. What's not to like?
It works for none liveaboards with solar who live on a mooring. Total investment is just the cost of a low output B2B to ensure your engine starts when you arrive at the boat
Baggywrinkle
Well-known member
The OP has 300Ah of AGMs ..... in what universe is that a large house bank? AGM charge current should be between 0.10 and 0.15 of the C20 AH rating. So a 300 AH battery bank should be charged at between 30 and 45 Amps - that does not require a high output alternator.
Use of a Cyrix or an Argofet will allow the alternator to directly supply both house and starter banks with full power - there really is no tangible benefit to connecting the alternator just to the house bank and then using a B2B to charge the starter.
The OP also stated that his starter is his windlass battery, so throttling the alternator output through a B2B to the windlass/starter battery when pulling up many meters of chain will mean that the heavy lifting is literally being done by an unassisted starter battery - even with the engine running. With your suggestion, the alternator -> B2B will be contributing a measly 10-18A to the task with the battery providing the rest. A 1000W windlass will pull around 85-90A while recovering the chain - the majority of that should really be coming from the alternator, not the battery. This is yet another reason to ensure the alternator can directly supply the starter battery.
At the end of the day, it doesn't matter what liveaboards do, the OP has a specific problem and the solution you propose for his specific setup is definitely sub-optimal. I get that your proposal works on your boat and others like it, if you choose to do it that way then fine, it's your boat, but consider the OPs problem rather than dogmatically pushing what you see to be the only solution.
In summary:
Your proposal means the charge light on the engine panel can no longer be relied on to show that the starter battery is being charged - you need the B2B on and a BT app to work that out.
The starter won't be charged very fast and the alternator can't effectively assist the windlass - while the starter battery heats the glowplugs, starts the engine, and pulls up the anchor chain then the alternator is only able to provide a measly 10-18A through a B2B.
When the engine isn't running, the B2B will see varying input voltages due to the MPPT 3 phase charging combined with the house loads, and it must be configured to work properly - with the danger that it will end up as a parasitic load on the house bank.
There is also no out of the box solution to allow engine start from the house bank in an emergency, you would have to rig your own solution.
For the OP, his own first suggestion is the way to go IMO.
... with the proviso to make sure the batteries are all the same chemistry.
Proposal 2 doesn't charge the battery not connected to the MPPT, and proposal 3 is effectively the B2B proposal which we have now discussed to death.
geem
Well-known member
Connect the windlass to the house battery. Mine has been like that for 10 years.
You obviously can't get your head around the fact that the big loads on a boat can all be run from the house battery. Its the biggest battery so use it for the large loads. It can have solar to give it good 3 stage charging and alternator charging. The tiny load of an engine pulling 80A for about 1/2second are easily met by B2B. Why do you want to make it so complicated?
Baggywrinkle
Well-known member
.... with a Cyrix, the starter battery becomes a house battery when it needs to be and an isolated starter battery when it needs to be .... I guess you could connect everything to the house battery, following your logic then you don't even need a starter battery or a bow-thruster battery .... lol
... and you have created one massive, single, complicated, point of failure because the two things you need to rely on to be able to bug-out - windlass and engine start are not isolated from the rest of the boat. Way to go 
geem
Well-known member
Why would you do that? It's stupid. Separating the engine battery is obvious. Keeping in perfect condition on a 3 stage charge is obvious. Running your main loads from the big battery is obvious. If you want a single point of failure carry on. Technology has moved on since the 1970s when engine had a battery and the cabin lights had a battery. Now boats have huge loads. You need to think differently..... with a Cyrix, the starter battery becomes a house battery when it needs to be and an isolated starter battery when it needs to be .... I guess you could connect everything to the house battery, following your logic then you don't even need a starter battery or a bow-thruster battery .... lol
sailoppopotamus
Active member
Thanks to both of you for your posts, I've been following the discussion with great interest. I'd like to draw your attention to this very pertinent article by a professional marine electrician, as well as episodes 10, 11, 27 and 38 of this series of videos on boat electrics. These resources go into some detail on the merits and drawbacks of battery combiners.
In an earlier post I wondered about what happens when the battery combiner closes during charging, with the two batteries in a disparate state of discharge, expressing concern that one of the batteries is kept at an absorption rather than float voltage when it isn't necessary. Reading the above sources I get the impression that this is only a concern in theory, but in practice it just doesn't impact the longevity of the (starter, in my case) battery. I was also concerned that charge may flow during charging from the (effectively full) starter battery to the (less full) house battery -- this is not a valid concern as explained in my first link.
Just a few thoughts I had on the matter
- In the wiring diagram I posted, I had a Victron Orion Tr between the house and starter battery. On one hand this is an overkill for the purposes of charging my starter battery, which a trickle charger could accomplish just as well. On the other hand, the 18A model is undersized, as it is only going to feed that much to the starter battery when running the windlass, which is less than my 35A alternator + 10A or so of solar. Therefore if I go down the B2B route I'm better off wiring the windlass to the house battery -- that is probably going to be fine, but I acknowledge the risk that some of my electronics might not like it. At any rate, the alternator and windlass should be wired together. In this respect the B2B solution is restrictive, since it won't allow me to connect the windlass to the start battery without sacrificing the ability to charge both banks with the alternator (without an Argofet).
- The lack of emergency start in the proposed B2B solution is a severe drawback. But this could be solved easily with a switch to isolate the B2B, and a jump-starting wire (which I already have on board in lieu of a 'Both' button).
- If the B2B fails, the starter battery won't charge. This is no biggie as long as the arrangements for the emergency start are in place. Either way, I don't have an engine panel alarm to warn me about this, or even a voltmeter for the starter battery (!) so the light on the charger would be the only way of knowing this has happened.
All in all, I've spent a lot of time thinking about this and have come to a conclusion that both solutions are actually good, which is perhaps why I'm having so much trouble with this. The B2B has the advantage of always keeping the batteries in isolation, but is significantly more expensive, and requires me to run the windlass off the house battery if I want to take full advantage of the alternator. The Cyrix is cheaper, allows more flexibility in the windlass/alternator wiring, but has the disadvantage of not isolating the batteries completely.
At this stage I will admit that I'm seriously tempted to forgo the B2B and just go with a Cyrix as @Baggywrinkle suggests. It's a 130 euro difference, which might be better spent elsewhere. Even if this arrangement does somewhat reduce the life of the start battery, which from the links I posted above doesn't really seem to be the case, it's still cheaper to save the 130 euros now. I'll have to make up my mind tonight as I'm going to the shop tomorrow to pick up the various bits and pieces.
In an earlier post I wondered about what happens when the battery combiner closes during charging, with the two batteries in a disparate state of discharge, expressing concern that one of the batteries is kept at an absorption rather than float voltage when it isn't necessary. Reading the above sources I get the impression that this is only a concern in theory, but in practice it just doesn't impact the longevity of the (starter, in my case) battery. I was also concerned that charge may flow during charging from the (effectively full) starter battery to the (less full) house battery -- this is not a valid concern as explained in my first link.
Just a few thoughts I had on the matter
- In the wiring diagram I posted, I had a Victron Orion Tr between the house and starter battery. On one hand this is an overkill for the purposes of charging my starter battery, which a trickle charger could accomplish just as well. On the other hand, the 18A model is undersized, as it is only going to feed that much to the starter battery when running the windlass, which is less than my 35A alternator + 10A or so of solar. Therefore if I go down the B2B route I'm better off wiring the windlass to the house battery -- that is probably going to be fine, but I acknowledge the risk that some of my electronics might not like it. At any rate, the alternator and windlass should be wired together. In this respect the B2B solution is restrictive, since it won't allow me to connect the windlass to the start battery without sacrificing the ability to charge both banks with the alternator (without an Argofet).
- The lack of emergency start in the proposed B2B solution is a severe drawback. But this could be solved easily with a switch to isolate the B2B, and a jump-starting wire (which I already have on board in lieu of a 'Both' button).
- If the B2B fails, the starter battery won't charge. This is no biggie as long as the arrangements for the emergency start are in place. Either way, I don't have an engine panel alarm to warn me about this, or even a voltmeter for the starter battery (!) so the light on the charger would be the only way of knowing this has happened.
All in all, I've spent a lot of time thinking about this and have come to a conclusion that both solutions are actually good, which is perhaps why I'm having so much trouble with this. The B2B has the advantage of always keeping the batteries in isolation, but is significantly more expensive, and requires me to run the windlass off the house battery if I want to take full advantage of the alternator. The Cyrix is cheaper, allows more flexibility in the windlass/alternator wiring, but has the disadvantage of not isolating the batteries completely.
At this stage I will admit that I'm seriously tempted to forgo the B2B and just go with a Cyrix as @Baggywrinkle suggests. It's a 130 euro difference, which might be better spent elsewhere. Even if this arrangement does somewhat reduce the life of the start battery, which from the links I posted above doesn't really seem to be the case, it's still cheaper to save the 130 euros now. I'll have to make up my mind tonight as I'm going to the shop tomorrow to pick up the various bits and pieces.
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PaulRainbow
Well-known member
In this instance, i would fit rhe Cyrix. Fitted to tens of thousands of similar boats without any of the claimed problems in this thread.
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