B2B sizing

Caladh said:
How do I know what size I need, and whether it should be isolated on non-isolated ? I currently (!) have 400a/h house bank and 90a/h start with 80w solar and main Sterling 30 amp charger.
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Based on the above there seems to be no reason to install a B2B.
I'd expect the alternator to be charging the starter battery direct, the solar panel to be charging the house bank direct and the sterling (presumably a multi output charger) to be charging both.
I'd expect there to be a vsr to link there two banks so that solar and alternator also charge both.

With a 400Ah battery bank a larger charger and much more solar charging would be appropriate
 
VicS said:
Based on the above there seems to be no reason to install a B2B.
I'd expect the alternator to be charging the starter battery direct, the solar panel to be charging the house bank direct and the sterling (presumably a multi output charger) to be charging both.
I'd expect there to be a vsr to link there two banks so that solar and alternator also charge both.

With a 400Ah battery bank a larger charger and much more solar charging would be appropriate
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Yes Vic i hav3 a plan for more solar. I had thought to get a VSR but understand a B2B is a better bet to get alternator to charge the batteries more efficiently under way with the engine. Alternator is 90 a/h from 1996.
 
Worst case scenario for recharging your 400AH house bank from the engine as fast as possible would mean you would want to take perhaps 70 amps from your alternator.
This would mean about 60amps through the B2B. So a max size for B2B. Any smaller would be fine but not recharge house bank so quickly and not make the most of your alternator. So longer engine run needed. If that is what you want. But not what I would see as a high priority. ol'will
 
Caladh said:
Yes Vic i hav3 a plan for more solar. I had thought to get a VSR but understand a B2B is a better bet to get alternator to charge the batteries more efficiently under way with the engine. Alternator is 90 a/h from 1996.
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You could wire the alternator directly to the domestic bank then use a small b2b to charge the engine battery. This would be economic in as much as a small output b2b would be sufficient to keep the engine battery charged. The benifit to this setup is that you get full alternator output to the domestic bank. I think it is a better setup than using a battery combiner like a VSR where one battery gets the voltage demanded by the other even if one battery is fully charged.
 
VicS said:
I'd expect the alternator to be charging the starter battery direct, the solar panel to be charging the house bank direct and the sterling (presumably a multi output charger) to be charging both.
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Please excuse the drift.
I have the three output Sterling charger but, if I remember correctly, the three outputs are merely commoned.
It seems the three outputs all depend on one feedback.
If one battery is fully charged, what happens to the outputs to the other two?
 
Caladh said:
……but understand a B2B is a better bet to get alternator to charge the batteries more efficiently under way with the engine.
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where have you got that understanding from? I have a VSR and it works fine. I think many have the same.

As a matter of interest, does your 1996 alternator provide 14.4v or so, or is it so old that it only provides about 13.5v?
 
Richard10002 said:
As a matter of interest, does your 1996 alternator provide 14.4v or so, or is it so old that it only provides about 13.5v?
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That seems the most relevant question. If around 14.4 volts then an additional boosting device seems redundant. If down as low as 13.5 volts then I would have thought a Sterling A2B would be more useful than a B2B. Unlike the B2B, the A2B has a heat sensor for the alternator, and because it also has un-boosted charge for the engine battery you can run separate circuits without need for a VSR or splitter.
 
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Richard10002 said:
where have you got that understanding from? I have a VSR and it works fine. I think many have the same.

As a matter of interest, does your 1996 alternator provide 14.4v or so, or is it so old that it only provides about 13.5v?
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Ok so I had a VSR on a previous boat which worked well with a smart charger on a Balmar 70 amp alternator. Perhaps you can therefore enlighten me as to the advantage a B2B provides over a dual VSR? I guess I’m trying to make sure the house and start banks are getting charged by the alternator as efficiently as possible.
 
Caladh said:
Ok so I had a VSR on a previous boat which worked well with a smart charger on a Balmar 70 amp alternator. Perhaps you can therefore enlighten me as to the advantage a B2B provides over a dual VSR? I guess I’m trying to make sure the house and start banks are getting charged by the alternator as efficiently as possible.
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If the alternator is outputting 14.4V and the VSR is closed (it should be), then all batteries will have the same terminal voltage and the alternator will put out as much current as the batteries can take. The engine battery will not take much, for long, (usually) so it's then exactly the same as having the alternator connected directly to the domestic bank, except that the charged engine battery will still have a 14.4V terminal voltage.

Geem has a point about the engine battery sitting at the absorption voltage of the domestic bank, but only in certain circumstances, to any degree. For instance, if you have a large solar array charging a deep cycle domestic bank at 14.8V, you would not want a VSR. In most cases, a VSR is perfectly acceptable, as you know from your last boat. My own boat has the batteries on charge every day during the Summer (solar panels) and during the Winter (when there's not enough Sun) 24/7 from the shore power, my engine battery has sat at 14.V all of those times, is about 5 years old and still in good condition.

If you don't fancy a VSR, how about a Victron Argofet ? It will charge all batteries from the alternator with low voltage loss, but you could leave the solar panels only connected to the domestic bank. Of course, when running the engine or on shore power all batteries will still be at the same terminal voltage.

IMO, a VSR is suitable for your needs.
 
Would fitting a Sterling Alternator to battery charger be a good option, thats what we use with a 100A alternator with 300AH domestic and 75AH engine battery. At normal cruising of 2500 rpm, we charge at circa 60 to 70 amps. This device boosts the charge voltage (and so current) to the house batteries but has a separate lower voltage output to the engine battery. Seems to work well, keep an eye on alternator temperature however, we fitted an extra cooling fan and remote temperature gauge.
 
yotter said:
Would fitting a Sterling Alternator to battery charger be a good option, thats what we use with a 100A alternator with 300AH domestic and 75AH engine battery. At normal cruising of 2500 rpm, we charge at circa 60 to 70 amps. This device boosts the charge voltage (and so current) to the house batteries but has a separate lower voltage output to the engine battery. Seems to work well, keep an eye on alternator temperature however, we fitted an extra cooling fan and remote temperature gauge.
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As the OP's alternator is charging at 14.4V it wouldn't worth fitting the A2B charger, as boosting the voltage in excess of 14.4V is going to be doing the batteries no favours. Unless, of course, the OP's batteries need a charging voltage greater than 14.4V
 
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PaulRainbow said:
If the alternator is outputting 14.4V and the VSR is closed (it should be), then all batteries will have the same terminal voltage and the alternator will put out as much current as the batteries can take. The engine battery will not take much, for long, (usually) so it's then exactly the same as having the alternator connected directly to the domestic bank, except that the charged engine battery will still have a 14.4V terminal voltage.

Geem has a point about the engine battery sitting at the absorption voltage of the domestic bank, but only in certain circumstances, to any degree. For instance, if you have a large solar array charging a deep cycle domestic bank at 14.8V, you would not want a VSR. In most cases, a VSR is perfectly acceptable, as you know from your last boat. My own boat has the batteries on charge every day during the Summer (solar panels) and during the Winter (when there's not enough Sun) 24/7 from the shore power, my engine battery has sat at 14.V all of those times, is about 5 years old and still in good condition.

If you don't fancy a VSR, how about a Victron Argofet ? It will charge all batteries from the alternator with low voltage loss, but you could leave the solar panels only connected to the domestic bank. Of course, when running the engine or on shore power all batteries will still be at the same terminal voltage.

IMO, a VSR is suitable for your needs.
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Ok ta Paul. Can’t help thinking you recommended a B2B when I was asking about replacing a Bosch relay which is currently in the circuit, some time ago.
 
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