Charging Question - is a battery to battery charger the right way forward?

[West Coast]

Hi all, been considering this question for a few months now, reading threads and consulting manufacturers websites, so think I have a way forward. But before proceeding, would appreciate comments and advice if I have this correct.

System is 12 volt. Alternator is an Hitachi, 80 amp (fitted to Yanmar 54hp engine). Alternator seems to use an internal regulator, although I have not been able to identify all the wires on the back of the alternator (see piccie), I am wondering what the yellow one is, perhaps sensing battery voltage?



Alternator output is taken to a battery isolator, RCE 100-1E-3IG which is a electronic device of some kind with claimed very low voltage drop. The isolator has 3 outputs, which are used as follows:

A Single Engine battery, lead acid sealed 110Ah
B House batteries, 4 number, each lead acid sealed 110Ah
C Bow thruster batteries, 2 number, each AGM 50Ah (high current rating).

The system runs OK, but my objective is to charge the house batteries more quickly.

I fitted a Mastervolt Battery Monitor system last year so I could monitor what was going on. It has a simple voltage reading on Engine and Bow Thruster batteries (which are normally at rest) and current/voltage measuring on the House Batteries, also giving a % full reading.

If the house batteries start at say at 95%, overnight at anchor they can fall to around 75%. As you would expect, when engine is started, there is healthy current into the house batteries of initially around 30 - 35 amps. However this quickly falls to only around 15 amps (say 80% full) and then around 7 amps (90% full)

I understand the principles here, as the batteries become closer to fully charged, voltage rises and charge current falls. However, to charge the house batteries from say 75% full to 85% full takes around 2 hours and 85% to 95% takes around a further 4 hours.

I considered a smart controller on the alternator, but given I have mixed battery types and 3 battery sets with the isolator, this to me seems the wrong approach. I also considered a larger alternator, but this also seems wrong. I have reached the conclusion that the best approach would be to fit a Battery to Battery charger, with its input connected to the House Battery output of the isolator and output to the house batteries.

Does this seem the best plan? Should I be looking for a Battery to Battery charger, or an Alternator to Battery Charger (given I am not really charging from a battery, but an isolated output from the alternator)?

Cheers

 

[William_H]

The crux of the matter is that your charge rate goes down to 7 amps into house batteries. A charging device with "smart" charging regime can increase this number. So getting the house battery to a higher degree of charge with less engine running. Just how much is only found by fitting a smart controller of some sort. My opinion is perhaps not worth the cost/ trouble for the increase in charge rate.
However if you do think it worth while then the BtoB charger is an easily fitted solution. It takes the voltage given to it say 13.75 with engine running and converts it up to say 15v to push more charge into the battery. It does this at a controlled "smart" regime to ensure battery ins not overcharged. The converter however will operate at a power loss perhaps 90% efficient. The alternator will have to provide the added current. Experience will show if your alternator is then running near capacity or in fact current limited at the usual engine RPM. If so a larger alternator may be indicated.
As you realise an add on regulator to the alternator will increase the charge voltage in a "smart" way so achieve the same resuylt without the inefficiencies. However as you identified the different battery types might make it difficult to get the right charge regime.
I think ultimately your experience of how you use the whole system ie engine run time versus actual discharge use time is what matters. Or if aint broke don't fix it. As in if you don't find you are running out of 12v supply and find you have to start the engine to replenish don't fix it.
Lastly I am am very skeptical of volt meters that convert voltage to battery charge percentage. Actual voltage can be far more useful as it can vary with recency of discharge or charge. The really important part being voltages below 12v indicating near time to recharge. So my opinion do nothing just relax and enjoy. good luck ol'will

 

[West Coast]

I think ultimately your experience of how you use the whole system ie engine run time versus actual discharge use time is what matters. Or if aint broke don't fix it. As in if you don't find you are running out of 12v supply and find you have to start the engine to replenish don't fix it.
Lastly I am am very skeptical of volt meters that convert voltage to battery charge percentage. Actual voltage can be far more useful as it can vary with recency of discharge or charge. The really important part being voltages below 12v indicating near time to recharge. So my opinion do nothing just relax and enjoy. good luck ol'will

Sorry, should have said the boat is a sail boat. I used the engine more than I wanted last season simply due to lack of wind! Normally I would use the engine far less, so in normal circumstances I would have a problem. Hence the question.

Should also have said the mastervolt unit measures current (with a shunt) and voltage on the House batteries. It only looks at voltage on the Engine and Bow thruster batteries

 

[Mistroma]

The figures you quote were completely normal for my 42DS is Yanmar 4JH4AE (80A alt.) and 450Ah batteries. I'd agree that your 95%, 80%, 75% figure probably don't represent actual state of charge. Are you happy that you have configured the battery monitor for your system? Even the obvious one of capacity won't be accurate and could be wildly out. How new are your batteries? How well have they been treated, what's the charging regime etc. all affect their accuracy. Have you confirmed the battery state using temp. compensated Specific Gravity readings? Even that isn't easy as readings vary with make of battery and it's best to monitor regularly to build up a picture.

If you keep the boat on charge in a marina and only sail at weekends then you are likely to be starting from 100%. That's assuming your charger is setup correctly.

I have the Hitachi 80A LR180-03C (Yanmar part 119573-77201)
E Black Battery -ve
B Red Battery +ve
L Blue/Black (LB) Connects to charge warning alarm/lamp then ignition switch
R Red/Black (RB) Connect to ignition switch, for tachometer as far as I can remember
Y Yellow Internal IC regulator, not certain where it goes exactly (Orange on mine)

E & B are obvious, L & R from plastic T shaped connector to engine panel and Y is the fused one.
Pretty certain the Y one will go to the charge splitter to let the alternator IC regulator sense battery voltage.

I replaced all the battery wiring with much heavier wire and also replaced the charge splitter with a different system. The splitter and original wiring are still in place ready to connect again as a backup system. I seem to remember that the splitter has a sense wire connected. I assume I would have moved that but can't remember at present.

I thought about opening the alternator to modify the regulator but it hasn't really been worth it. My Smartgauge system would control the output by switching the mod. in and out to boost the Voltage. However, my solar array keeps the batteries fairly well charged and are a far better solution for my usage pattern. I run a Honda generator pretty infrequently when anchored for a week or two. Engine runs tend to be quite long when I do move and there's no wind.

I doubt you will get the batteries back to 100% very often without some sort of boost to the standard alternator. Batteries won't be fully charged unless you are motoring for at least 4-5 hours every day or on shore power a lot of the time. So certainly worth doing something.

It would be useful to get details of your boat, type of use, charging etc. You can check details of my system by looking at my profile if you want to compare with your setup (look at Extra_1..5 entries in profile).

 

[superheat6k]

So the single engine battery and three for the services are all similar.

Presumably once you are sailing or at anchor you are not using the bow thruster, with its AGM batteries.

I would install a smart alternator controller and manually isolate the bow thruster batteries from the charger say after 1/2 hour since the thruster was last used. It won't matter if you forget to de-isolate before next use as long as you have a reminder on your checklist to turn the alternator charger source back on when you next leave the boat. Indeed if you are on shorepower at your home berth perhaps consider having it the norm that the AGMs are left switched off from the alternator charge source, assuming they have a dedicated output from the shore-power charger. The short bursts of usage a thruster gets are not going to take that much from the AGMs, and with this arrangement you do have the option of turning the alternator source on for a period if you are on a longer trip, or find the thruster being used more.

 

[PaulRainbow]

I considered a smart controller on the alternator, but given I have mixed battery types and 3 battery sets with the isolator, this to me seems the wrong approach. I also considered a larger alternator, but this also seems wrong. I have reached the conclusion that the best approach would be to fit a Battery to Battery charger, with its input connected to the House Battery output of the isolator and output to the house batteries.

Does this seem the best plan? Should I be looking for a Battery to Battery charger, or an Alternator to Battery Charger (given I am not really charging from a battery, but an isolated output from the alternator)?

Your batteries are not really relevant, set a charging regime at the upper end of SLA batteries and the AGM ones will be fine.

A B2B charger is unlikely to be much help in this installation. You would have to disconnect the domestic bank from the current slit charge device and connect the B2B to the engine bank and the domestic bank. It would then act in a similar way yo a mains smart charger, taking it's supply power from the engine battery (pretty obvious). The problem would then be getting the Hitachi alternator to replace what the B2B was taking from the engine battery. In all likelihood the alternator would not be able to keep up, so the B2B would reduce it's output (or stop altogether) to stop the engine battery from being depleted.

A better alternator would be of more benefit than a B2B.

An even better solution would be to fit some solar panels. They will be charging all day, whether the engine is running or not, as long as the Sun is shining.

 

[Bobc]

Would replacing the diode splitter with an A to B charger be a better solution?

 

[PaulRainbow]

<snip> manually isolate the bow thruster batteries from the charger say after 1/2 hour since the thruster was last used. It won't matter if you forget to de-isolate before next use as long as you have a reminder on your checklist to turn the alternator charger source back on when you next leave the boat. Indeed if you are on shorepower at your home berth perhaps consider having it the norm that the AGMs are left switched off from the alternator charge source<snip>

There is no point disconnecting the AGM batteries, they are perfectly happy at SLA voltages and are also happy at slightly higher voltages. It's very common now to have AGM's for thrusters and i'm now routinely fitting them for engine start batteries, they live happily with SLA batteries.

 

[GHA]

The system runs OK, but my objective is to charge the house batteries more quickly.

I fitted a Mastervolt Battery Monitor system last year so I could monitor what was going on. It has a simple voltage reading on Engine and Bow Thruster batteries (which are normally at rest) and current/voltage measuring on the House Batteries, also giving a % full reading.

If the house batteries start at say at 95%, overnight at anchor they can fall to around 75%. As you would expect, when engine is started, there is healthy current into the house batteries of initially around 30 - 35 amps. However this quickly falls to only around 15 amps (say 80% full) and then around 7 amps (90% full)

I understand the principles here, as the batteries become closer to fully charged, voltage rises and charge current falls. However, to charge the house batteries from say 75% full to 85% full takes around 2 hours and 85% to 95% takes around a further 4 hours.

Doesn't sound too far out. What voltage are you seeing at the battery terminals during charging? And what voltage does the battery datasheet say for absorption voltage? Without knowing that it's tricky to say too much. Lead acid batteries take a very long time to get to fully charged, charge a bit quicker by upping the absorption voltage. sealed batteries will limit this, maybe you won't actually be able to gain much quicker charging time just based on the data sheet.

 

[West Coast]

I doubt you will get the batteries back to 100% very often without some sort of boost to the standard alternator. Batteries won't be fully charged unless you are motoring for at least 4-5 hours every day or on shore power a lot of the time. So certainly worth doing something.

It would be useful to get details of your boat, type of use, charging etc. You can check details of my system by looking at my profile if you want to compare with your setup (look at Extra_1..5 entries in profile).

Exactly my situation when away cruising. I am usually at anchor, and motoring per day is often only 1 - 2 hours (in and out of anchorages). I solved the problem on my last boat with a smart alternator controller, but that was a simpler set up (single engine battery, 2 house batteries and a VSR).

FWIW boat is a Jeanneau 439, built 2012, so has the typical french yard set up and equipment.

 

[pvb]

I considered a smart controller on the alternator, but given I have mixed battery types and 3 battery sets with the isolator, this to me seems the wrong approach. I also considered a larger alternator, but this also seems wrong. I have reached the conclusion that the best approach would be to fit a Battery to Battery charger, with its input connected to the House Battery output of the isolator and output to the house batteries.

Does this seem the best plan? Should I be looking for a Battery to Battery charger, or an Alternator to Battery Charger (given I am not really charging from a battery, but an isolated output from the alternator)?

I'd suggest you look carefully at fitting an Alternator-to-Battery charger. This will boost the voltage to your house batteries, to charge them faster. It will connect straight to your house batteries, and there are no modifications needed to the alternator. The A-to-B charger also has an isolated unboosted output to charge your engine battery. You can use your existing isolator between the unboosted output and the thruster batteries, so they will charge in just the same way as they do at the moment.

 

[West Coast]

Doesn't sound too far out. What voltage are you seeing at the battery terminals during charging? And what voltage does the battery datasheet say for absorption voltage? Without knowing that it's tricky to say too much. Lead acid batteries take a very long time to get to fully charged, charge a bit quicker by upping the absorption voltage. sealed batteries will limit this, maybe you won't actually be able to gain much quicker charging time just based on the data sheet.

Took a set of snapshot readings just before lift-out at the end of last season:
Engine running, readings on good quality digital multimeter
Volts at alternator terminals 14.3v
Isolator input voltage 14.0v
Isolator output voltages 14v/14v/13.9v
Charge current into house batteries 15 amps

I appreciate the 0.3v drop between the alternator and the isolator is an issue and am tracing the cables to find the reason. The negative cables go via a bolt stud on the engine which is corroded, so this is a likely culprit and is being sorted.

Would this 0.3 volt be significant in this discussion?

Dont have datasheets for the exide lead acid batteries so not sure of absorption voltage

 

[GHA]

I am usually at anchor, and motoring per day is often only 1 - 2 hours (in and out of anchorages). I solved the problem on my last boat with a smart alternator controller, but that was a simpler set up (single engine battery, 2 house batteries and a VSR)..

Unfortunately that actually sounds unlikely for lead acid down below 80%, just not possible to get back to 100% so quickly.

 

[West Coast]

A B2B charger is unlikely to be much help in this installation. You would have to disconnect the domestic bank from the current slit charge device and connect the B2B to the engine bank and the domestic bank. It would then act in a similar way yo a mains smart charger, taking it's supply power from the engine battery (pretty obvious). The problem would then be getting the Hitachi alternator to replace what the B2B was taking from the engine battery. In all likelihood the alternator would not be able to keep up, so the B2B would reduce it's output (or stop altogether) to stop the engine battery from being depleted.

OK, that makes sense

 

[GHA]

Took a set of snapshot readings just before lift-out at the end of last season:
Engine running, readings on good quality digital multimeter
Volts at alternator terminals 14.3v
Isolator input voltage 14.0v
Isolator output voltages 14v/14v/13.9v
Charge current into house batteries 15 amps

I appreciate the 0.3v drop between the alternator and the isolator is an issue and am tracing the cables to find the reason. The negative cables go via a bolt stud on the engine which is corroded, so this is a likely culprit and is being sorted.

Would this 0.3 volt be significant in this discussion?

Dont have datasheets for the exide lead acid batteries so not sure of absorption voltage

0.3V might not be much of an issue regarding charge time as that will tail off when the current drops off close to full charge anyway. Does sound a bit low voltage though, some sort of booster might help a bit though the battery max charge voltage rom the datasheets might not be too much higher than you have already. The voltages at the battery terminals are the really interesting ones.
Get some solar

 

[West Coast]

I'd suggest you look carefully at fitting an Alternator-to-Battery charger. This will boost the voltage to your house batteries, to charge them faster. It will connect straight to your house batteries, and there are no modifications needed to the alternator. The A-to-B charger also has an isolated unboosted output to charge your engine battery. You can use your existing isolator between the unboosted output and the thruster batteries, so they will charge in just the same way as they do at the moment.

Ah, OK, this sounds a plan. I had found such a unit from Sterling with 2 outputs, not 3, but using the isolator to further split the charge between the engine and bow thruster would make sense.

Sterling kit the best way to go?

 

[Bobc]

Ah, OK, this sounds a plan. I had found such a unit from Sterling with 2 outputs, not 3, but using the isolator to further split the charge between the engine and bow thruster would make sense.

Sterling kit the best way to go?

That's what I have and it sorted out my charging problems which were the same as yours.

 

[West Coast]

0.3V might not be much of an issue regarding charge time as that will tail off when the current drops off close to full charge anyway. Does sound a bit low voltage though, some sort of booster might help a bit though the battery max charge voltage rom the datasheets might not be too much higher than you have already. The voltages at the battery terminals are the really interesting ones.
Get some solar

Also took voltage readings from the mastervolt unit at the same time as the other readings, the mastervolt sensing wires are directly on the battery terminals. They showed House = 13.80v, Engine 13.96v and Bow Thruster = 13.97v. I did not use the multimeter to check these volt readings on the battery terminals, will do next time taking snapshot readings!

Solar is on the agenda, but initial focus is making best efficient use of the engine.

 

[PaulRainbow]

The Hitachi alternator is internally temperature compensated. Any attempts to force it to put more volts out will likely prove unsuccessful. AtoB, BtoB or external smart regulators will almost certainly raise the alternator temperature, which won't end well.

If you want more from the engine charging the only real way forward is to fit a better alternator, such as a Balmar. However, this is expensive and you'll still only be running the engine for short periods.

For spending time off grid solar is the best way to go.

 

[West Coast]

The Hitachi alternator is internally temperature compensated. Any attempts to force it to put more volts out will likely prove unsuccessful. AtoB, BtoB or external smart regulators will almost certainly raise the alternator temperature, which won't end well.

Not sure I understand - I thought the idea of the A-B was to lower the voltage seen at the A-B input to encourage the alternator to give higher current. The A-B converter then outputs higher voltage (with lower current) to charge the batteries. So the alternator voltage is not rising, but it is giving higher current. The Hitachi is 80 amp but appreciate this is max output (not continuous), so even at say 30 amp continuous output, it is running at 38% capacity which should not cause overheat?

Or am I missing something?