Battery to battery charging

[morgandlm]

I currently have a fairly simple two battery set-up of lead acid starter and domestic batteries each with a battery isolator. Both batteries are charged from the alternator through a Victron Cyrix VSR. I’m planning to remove the VSR and install a battery to battery charger but am undecided between a Victron Orion TR Smart 18 amp unit or a Sterling Power Saturn BB1225 which is rated at 25 amps. The Beta engine has a 40 amp alternator so the Sterling is perhaps over-rated?
I note that the Victron relies on an external heat sink for cooling whereas the Sterling has an internal cooling fan. I’d be grateful for any advice on the selection and feedback from anybody who has fitted either of these.
The domestic battery is currently a sealed lead acid but when it needs replacing I may upgrade to a LiFe PO4.
David Morgan

 

[Tranona]

Can't see any reason to use a B2B with you current batteries. Their charge rate is limited to what they can accept rather than the output of the alternator. The B2B would be necessary if you go lithium to avoid charging direct from the alternator as the acceptance rate is likely to overload the alternator which needs either to be better regulated or not used to charge direct. You don't say what size your domestic bank is but you describe is as "simple" so would guess unlikely to be bigger than a 40 amp alternator can deal with.

Ignoring the lithium option what are you hoping to achieve with a B2B?

 

[morgandlm]

The plan was to get the domestic battery more efficiently charged as result of the B to B having a pre-programmed algorithm which gives a better charging profile so gets more Ah into the battery without damaging it. I used to have a Sterling external battery sensing regulator which worked well but has a tap into the alternator which invalidates the warranty.= ( its a new engine) My hope was that the B to B would achieve the same thing .... am I wrong?

David Morgan

 

[Tranona]

Charging is limited by the acceptance rate of the battery. The latest alternator will regulate for maximum charge as appropriate. The Sterling works by upping the voltage which was necessary with older style alternators. I have a new Beta 30 (70A alternator) and a 190Ah AGM bank and I never see more than 15A going in, but I keep well within the suggested 50% SOC and once you get above that the acceptance rate quickly falls. It is only at low SOC that you require higher charge rates and even then unless you have a large bank, well within the output of your alternator. Suggest you spend the money on a bigger domestic bank so that you avoid going down to low SOC.

 

[Daverw]

I did this last year, fitted the new Victron Orion which is rated at. 50 amp and quite a lot small than previous model and with no heat shrink, the reason for this was to prepare for lithium upgrade which I’m just in the process of completing. Prior to this I had vsr which worked as needed for the agms, did change this for Argofet when started splitting the house and starter wiring again in prep for lithium project.

Luckily as most redundant kit as it was removed had £ value helped finance the next part.

Agree with others though if not planing of upgrading house to lithium cannot see the value of fitting b2b as you will actually loose some power with the B2B, Victron report 96% efficiency though so not much, the old model was reported to be only 60%

 

[Neeves]

If Geem does not add to the thread - I recall he reported adversely to a Victron unit (one of the few adverse Victron comments and normally he is supportive of Victron) as it overheated and had a reduced rate of charge. He tried using a computer fan, or 2, without success. You could send him a PM - as it was a few weeks ago and I do not recall the detail.

If you install Lithium and use it, as is possible, to a low SOC then it will take for ever, or a long time, to recharge to near 100% dependent on a B2B. It will take even longer than forever if you intend adding a larger Lithium battery bank - and your engine run times will be high. You don't mention how big a Lithium bank nor whether you have a large, or intend to have a large, solar array.

Jonathan

 

[Poecheng]

Agree with Tranona FWIW. Previous boat had 2005 Beta 20 and current boat has 2010 Yanmar 40. I have previously installed Adverc on Bukh 36 which did improve things but, measuring both boats' voltage and capacity carefully (some might say obsessively), I have not found the need to do anything about the charging circuits and I have a spare Adverc hanging around.
If I may suggest, the best improvements generally are
* solar panel (potentially also having the facility for flying panels) and Victron MPPT
* smaller engine battery (it will take almost nothing to start a small Beta), emergency link and additional domestic battery.

A story with a purpose: We left the car (BMW320d tourer, therefore 184hp diesel) for a couple of months at the marina having headed off this summer. On our return the battery was dead-ish and incapable of starting the car, which was not welcomed! By a complete fluke and after asking around, we met visitors and one of the chaps had just been given a new Nico boost but had never been able to use it in anger. Bingo ! It was simply amazing and started the car instantly.

I am sure there is a downside somewhere (and will soon be told )but, as I have never discharged the domestic bank anywhere near the point it would not start a large engine, let alone the ones I have actually had/have, I wonder whether the batteries could all be combined for dual purpose and, if things go wrong, have a Nico boost to hand - walk it between boat and car.

 

[PaulRainbow]

The plan was to get the domestic battery more efficiently charged as result of the B to B having a pre-programmed algorithm which gives a better charging profile so gets more Ah into the battery without damaging it.

You will not get more ah in, it will likely be less, the B2B will be limited to 18a or 25a, whereas the alternator is 40a. Plus, the charge rate is limited by the battery resistance (as per post post #4)

I used to have a Sterling external battery sensing regulator which worked well but has a tap into the alternator which invalidates the warranty.= ( its a new engine) My hope was that the B to B would achieve the same thing .... am I wrong?

David Morgan

Sorry, but you are mistaken here. The B2B doesn't do the same thing as the Sterling regulator.

 

[William_H]

As I understand both the B2B and the smart alternator regulator provide a profile of high voltage ie 15+ to get more amps into the battery until near full when voltage is backed off to float in a suitable profile.
I under stand that a modern alternator with built in regulator will provide 14volts perhaps a little more at all times.
So yes for a short engine run you should get more AH into a low battery or half full battery with the B2B or the smart regulator.
However the plain engine fitted alternator regulator should be able to push a fair bit of charge into batteries via the VSR as it is.
What OP needs is an amp meter on the batteries indicating exactly how much current is going in to the batteries when being charged. he will see when the charge current has fallen so far as to make engine run not sufficiently productive for battery charging.
If this result is not enough for him then perhaps the B2B will give more charge. it will still be limited by alternator capacity (not rated capacity but that possible at the actual engine revs.
I suspect that improvement with B2B as already intimated will be disappointing.
As said, another way to get more AH into batteries with short engine run is to add more batteries. They may not get to full charge but will make more power available for discharge use. ol'will

 

[[70521]]

Your current system is working. Save your beer tokens and if you want to spend out on this new fangled Lithium in the future then make the change then.

 

[PaulRainbow]

As I understand both the B2B and the smart alternator regulator provide a profile of high voltage ie 15+ to get more amps into the battery until near full when voltage is backed off to float in a suitable profile.
I under stand that a modern alternator with built in regulator will provide 14volts perhaps a little more at all times.
So yes for a short engine run you should get more AH into a low battery or half full battery with the B2B or the smart regulator.
However the plain engine fitted alternator regulator should be able to push a fair bit of charge into batteries via the VSR as it is.
What OP needs is an amp meter on the batteries indicating exactly how much current is going in to the batteries when being charged. he will see when the charge current has fallen so far as to make engine run not sufficiently productive for battery charging.
If this result is not enough for him then perhaps the B2B will give more charge. it will still be limited by alternator capacity (not rated capacity but that possible at the actual engine revs.
I suspect that improvement with B2B as already intimated will be disappointing.
As said, another way to get more AH into batteries with short engine run is to add more batteries. They may not get to full charge but will make more power available for discharge use. ol'will

How will a 18a or 25a B2B charge the batteries faster than a 40a alternator ?

If you charge LA batteries at 15+ volts they aren't going to last very long, the Victron LA profiles do not charge at anything like that, they will be hardly (if at all) any higher voltage than the OPs new alternator.

He will be swapping a 14+v 40a alternator for a 14+v 18a DC-DC charger, that's slower charging in my book.

DC-DC chargers come into their own if you want to charge 12v batteries from 24v batteries, or you are fitting Lithium and it's only one solution of several for Lithium.

 

[Trident]

I can't see any reason to swap from the VSR - its a good piece of kit, works well and the B2B will not add anything and may do less - all for the princely sum of quite a lot
If you eventually change to LFP then a B2B is a good idea. Take a look at Renogy when the time comes - less expensive, very well made (I've fitted dozens over the last 5 years with zero issues) and have a fan built in as well as heatsink so stay nice and cool .. but for now just keep the VSR .

 

[Pye_End]

A quick look at the Sterling site - like the AB charger, the BB allows multi stage charging on the domestic bank.

With Lithium lurking somewhere in the future for all, a BB upgrade rather than an AB upgrade looks to make more sense.

Surely with higher appropriate stage voltages charging times should be better than using alternator alone, and multi stage is better for the battery?

 

[mattonthesea]

If you do go down the B2B route just be aware that the Sterling fan can be very loud!

 

[William_H]

How will a 18a or 25a B2B charge the batteries faster than a 40a alternator ?

If you charge LA batteries at 15+ volts they aren't going to last very long, the Victron LA profiles do not charge at anything like that, they will be hardly (if at all) any higher voltage than the OPs new alternator.

He will be swapping a 14+v 40a alternator for a 14+v 18a DC-DC charger, that's slower charging in my book.

DC-DC chargers come into their own if you want to charge 12v batteries from 24v batteries, or you are fitting Lithium and it's only one solution of several for Lithium.

The whole concept of smart or staged charging voltage either by alternator control or B2B is to overcome the problem that as the actual voltage of the battery rises with charge it takes (a lot) less current. So by boosting the charge voltage you can force more current in to the battery to get closer to full charge more quickly.
I don't believe batteries suffer from the higher charge voltage simply because by the time the battery takes the higher current the voltage is somewhat lower. Of course the idea relies on reducing the charge voltage when the battery is sensed to be charged. Generally in practice the charge current is a lot less than the capabilities of the charger.
So a charging source with profiled charge voltage should get the battery to take more current for longer into the charge period. Certainly more than an alternator set up to charge at 13.75 to 14 volts.
In practice I am not sure this is so valuable unless a sailor often runs the engine purely to charge the batteries. ol'will

 

[Alex_Blackwood]

The whole concept of smart or staged charging voltage either by alternator control or B2B is to overcome the problem that as the actual voltage of the battery rises with charge it takes (a lot) less current. So by boosting the charge voltage you can force more current in to the battery to get closer to full charge more quickly.
I don't believe batteries suffer from the higher charge voltage simply because by the time the battery takes the higher current the voltage is somewhat lower. Of course the idea relies on reducing the charge voltage when the battery is sensed to be charged. Generally in practice the charge current is a lot less than the capabilities of the charger.
So a charging source with profiled charge voltage should get the battery to take more current for longer into the charge period. Certainly more than an alternator set up to charge at 13.75 to 14 volts.
In practice I am not sure this is so valuable unless a sailor often runs the engine purely to charge the batteries. ol'will

In the "Old days, when I were a lad" Before all this new fangled stuff, there were two types of battery charging. Constant voltage and Constant current. With Constant voltage the current reduced as the battery charged. With Constant current the voltage increased as the battery charged. The latter at the appropriate 10 or 20 Hr. rate was the preferred method. (A 100ahr battery would be charged at 10 amps for 10Hrs or 5 amps for 20Hrs.) With constant voltage the battery would be charged at XX volts until the charge voltage and battery voltage were equal and the current virtually Zero.
PS You had to keep an eye on the SG to ascertain state of charge!

 

[PaulRainbow]

The whole concept of smart or staged charging voltage either by alternator control or B2B is to overcome the problem that as the actual voltage of the battery rises with charge it takes (a lot) less current. So by boosting the charge voltage you can force more current in to the battery to get closer to full charge more quickly.
I don't believe batteries suffer from the higher charge voltage simply because by the time the battery takes the higher current the voltage is somewhat lower. Of course the idea relies on reducing the charge voltage when the battery is sensed to be charged. Generally in practice the charge current is a lot less than the capabilities of the charger.
So a charging source with profiled charge voltage should get the battery to take more current for longer into the charge period. Certainly more than an alternator set up to charge at 13.75 to 14 volts.
In practice I am not sure this is so valuable unless a sailor often runs the engine purely to charge the batteries. ol'will

If you charge LA batteries at 15+ volts they will gas, a lot. 15v is an equalisation voltage and is not to be used on sealed batteries as they cannot be topped up. If you do they die very quickly.

A B2B is not there to increase charging voltage to that level. It is used in a Lithium installation to protect the alternator, a system with different battery voltages or sometimes in a system where the alternator is not capable of providing a high enough voltage to charge the batteries properly. In the latter case, it only raises the voltage to the correct level for the batteries, not to increase the voltage to one that tires to "force" charge the batteries at the expense of killing them off in a very short time.

Modern alternators have long since output voltages higher than 13.75 to 14.0 volts. The OP has a brand new engine with a brand new alternator, it will output an appropriate voltage and he will gain nothing from changing the VSR for a B2B, apart from an emptier bank account.

 

[Pye_End]

If you charge LA batteries at 15+ volts they will gas, a lot. 15v is an equalisation voltage and is not to be used on sealed batteries as they cannot be topped up. If you do they die very quickly.

A B2B is not there to increase charging voltage to that level. It is used in a Lithium installation to protect the alternator, a system with different battery voltages or sometimes in a system where the alternator is not capable of providing a high enough voltage to charge the batteries properly. In the latter case, it only raises the voltage to the correct level for the batteries, not to increase the voltage to one that tires to "force" charge the batteries at the expense of killing them off in a very short time.

Modern alternators have long since output voltages higher than 13.75 to 14.0 volts. The OP has a brand new engine with a brand new alternator, it will output an appropriate voltage and he will gain nothing from changing the VSR for a B2B, apart from an emptier bank account.

What voltages will this alternator give?

The spec of a Sterling 4 stage BtoB charger talks about 14.8v for open lead acid, or 14.4v for sealed as a boost, and then ultimately decreasing to float.

For best effect Sterling recommend open lead acid. OP is using sealed, so 14.4 would be the setting for boost before float. How does that compare with the alternator behaviour?

 

[[203264]]

An alternator will not put out its maximum rated current continuously. Certainly not when motor-sailing or charging at moderate revs. Think more like 50% or less. So the 40 amp alternator is more like 20 amps in the real world.

A B to B charger uses a proper charging profile which raises the voltage above alternator voltage, and lowers it, as appropriate. This will achieve longer life for your batteries. Reducing sulfation. This will result in reduced costs over time. This can be offset against the £135 for the Victron for example.

You will only ever get 80%-ish charge from an alternator - you will get 100% from a B to B charger.

I therefore propose that a Battery to Battery charger is better all round than direct alternator charging with a relay. Just size it to your battery capacity. Don't have a charger that is bigger than 20% of the house bank battery capacity (in Ah) for lead acid. Therefore the Victron would seem like a good bet.

If you do change battery chemistry in the future, a charger will cope with the mix. But there are other factors to consider with lithium.

This video does a fine job of explaining it better than I can:

Hope this helps

 

[William_H]

An alternator will not put out its maximum rated current continuously. Certainly not when motor-sailing or charging at moderate revs. Think more like 50% or less. So the 40 amp alternator is more like 20 amps in the real world.

A B to B charger uses a proper charging profile which raises the voltage above alternator voltage, and lowers it, as appropriate. This will achieve longer life for your batteries. Reducing sulfation. This will result in reduced costs over time. This can be offset against the £135 for the Victron for example.

You will only ever get 80%-ish charge from an alternator - you will get 100% from a B to B charger.

I therefore propose that a Battery to Battery charger is better all round than direct alternator charging with a relay. Just size it to your battery capacity. Don't have a charger that is bigger than 20% of the house bank battery capacity (in Ah) for lead acid. Therefore the Victron would seem like a good bet.

If you do change battery chemistry in the future, a charger will cope with the mix. But there are other factors to consider with lithium.

This video does a fine job of explaining it better than I can:

Hope this helps

Quite so except of course the AB to B charger can not supply any more current to the battery than the alternator is able to supply. Indeed somewhat less due to conversion inefficiencies. You will not get 100% rated current from AB to B if you have not got the capacity of the alternator (size and engine RPM) to supply it.
The real advantage of the enhanced voltage charging profile is to get the battery to take more current as it gets charged. So even if your alternator can only supply 20 amps the AB to B can ensure that the batteries will take near 20 amps through a larger portion of the charging process. ie quicker to get to near 100% charge. ol'will