Will I cook my starter battery by fitting a smart charger

[superboots]

I have a 60 amp alternator which charges through a buffer diode and gives the engine start battery 88 ah priority before charging the the service batteries 3 x 140 ah - all 12 volt
I have a mastervolt 90 amp alternator with external regulator which I want to fit. It has been suggested that if I do this I risk cooking the starter battery -Is this so? What should I do to avoid this? Also I am also thinking of adding 2 more service batteries and maybe some solar panels . Would this be an added problem?

 

[VicS]

I have a 60 amp alternator which charges through a buffer diode and gives the engine start battery 88 ah priority before charging the the service batteries 3 x 140 ah - all 12 volt
I have a mastervolt 90 amp alternator with external regulator which I want to fit. It has been suggested that if I do this I risk cooking the starter battery -Is this so? What should I do to avoid this? Also I am also thinking of adding 2 more service batteries and maybe some solar panels . Would this be an added problem?

If the alternator is regulated to the correct voltage there will be no problem. The battery will only draw the current it requires provided the alternator is so regulated.

Not sure what you mean by "buffer diode" ?

With two banks you have two basic choices:

• A diode splitter, which due to volts drop really requires the alternator to be battery sensed
  
• A VSR which does not suffer volts drop and can be installedto give priority charging to the battery bank you choose.

There are of course a variety of electronic devices to choose from as well.
Eg X-Split or a Sterling Alternator to Battery charger

 

[ghostlymoron]

A diode splitter does not prioritise either battery bank - it simply prevents the batteries discharging into one another. The charge from the alternator or other source will be split between the battery banks according to the internal resistance of each battery. i.e. the lowest charged will be topped up first.
To prioritise the starter battery, you need a VSR which will bring that battery up to fully charged state before switching to the house battery (unless you are American when you will have it connected the other way round!) The VSR solution is much better in my view as it means the starter battery is always fully charged.

 

[boatmike]

I have a 60 amp alternator which charges through a buffer diode and gives the engine start battery 88 ah priority before charging the the service batteries 3 x 140 ah - all 12 volt
I have a mastervolt 90 amp alternator with external regulator which I want to fit. It has been suggested that if I do this I risk cooking the starter battery -Is this so? What should I do to avoid this? Also I am also thinking of adding 2 more service batteries and maybe some solar panels . Would this be an added problem?

There could indeed be a problem if your service battery bank is significantly larger than your starting battery. The smart charger senses the service battery (usually) and if this is run down when the starter battery is not the "smart" charger will raise the voltage on both to 14.8 volts (or thereabouts) to "boost" the charge in the one sensed. It is quite possible that the starter battery (which only needs a 13volt float charge when full) will gas at this level and need constant monitoring for electrolyte level. Theoretically it won't harm the battery if you constantly monitor electrolyte level but if you let it run dry it will suffer terminally.

A better solution is to fit your larger alternator but replace the diode with a system like Merlin's smartbank. A simple relay system will work but smartbank is better. Combine it with smartgauge and you can monitor both batteries at the same time!

I don't have any connection with the company but that is what I have and it works extremely well. Go to their website www.merlinequipment.com and look under "split charging" There is a very good explanation of the problem there. Yes it's a sales pitch, but I can't argue with their logic. At least give it a read....

 

[pvb]

A better solution is to fit your larger alternator but replace the diode with a system like Merlin's smartbank. A simple relay system will work but smartbank is better. Combine it with smartgauge and you can monitor both batteries at the same time!

But Smartbank is essentially only a parallelling relay, which means that both the start and domestic batteries will be subjected to the same voltage.

 

[mitiempo]

A VSR (ACR over here) will parallel the batteries when a charging voltage is sensed.

 

[nigelmercier]

A diode splitter does not prioritise either battery bank - it simply prevents the batteries discharging into one another. The charge from the alternator or other source will be split between the battery banks according to the internal resistance of each battery. i.e. the lowest charged will be topped up first.
To prioritise the starter battery, you need a VSR which will bring that battery up to fully charged state before switching to the house battery (unless you are American when you will have it connected the other way round!) The VSR solution is much better in my view as it means the starter battery is always fully charged.

Pity, you started off well, but then fell into the same trap. A VSR does not prioritise either battery, all is does is short them together if there is charging voltage available - just like a pair of diodes does. But unlike diodes, there is no voltage drop. Connecting it "the other way around" also makes no difference, other than selecting which battery is always connected to the alternator, and which is switched.

 

[Relax]

The VSR I have fitted (sorry can't remember the make) is battery sensed - it only switches in the 'secondary' battery bank, the house bank in my case, when it senses a voltage of (I think) 13.8 and then disconnects when this goes down to something like 13.4.

Its actually a motorised switch with a time delay which prevents fluttering, rather than a relay as such.

 

[mitiempo]

Since bulk charging is between 14.2v and 14.6 give or take your VSR closes when charging starts, paralleling the banks. 13.4 is too high for a VSR to open as it probably means the other bank would not get a float charge. The Blue Seas VSR opens separating the banks at 12.35 after 10 seconds and 12.75 at 30 seconds. Battery sensing is normal.

 

[SvenglishTommy]

I have a 60 amp alternator which charges through a buffer diode and gives the engine start battery 88 ah priority before charging the the service batteries 3 x 140 ah - all 12 volt
I have a mastervolt 90 amp alternator with external regulator which I want to fit. It has been suggested that if I do this I risk cooking the starter battery -Is this so? What should I do to avoid this? Also I am also thinking of adding 2 more service batteries and maybe some solar panels . Would this be an added problem?

I often wondered about this too, both with smart regulators and battery chargers that sense and base their charging regime on the house bank. I must say I have never found the starter bank needs more water than the house, so I guess it is not gassing excessively in my setup, but my house bank is only 160AH. Maybe the empty house banks are so greedy that there isn't enough current to bother the starter bank, but maybe with large bank differences it could be a problem.

You could always just isolate the starter after a while if you know you're bringing up a very low house bank via a long engine run, and then switch it back in when it starts to float.

 

[sailinglegend420]

I have a 60 amp alternator which charges through a buffer diode and gives the engine start battery 88 ah priority before charging the the service batteries 3 x 140 ah - all 12 volt
I have a mastervolt 90 amp alternator with external regulator which I want to fit. It has been suggested that if I do this I risk cooking the starter battery -Is this so? What should I do to avoid this? Also I am also thinking of adding 2 more service batteries and maybe some solar panels . Would this be an added problem?

To try and simply answer the original posting.

Your starter battery could already be cooked!

Fitting a larger alternator would not make any difference. Its the charging voltage sitting across the starter battery for much longer than necessary that does the damage.

This is a complex subject so check out the download documents on split charging here:
http://www.power-store.com/view-item.asp?itemid=2186&id=365&

Other thoughts:

If you are fitting the 90 Amp alternator as a second alternator then you will fry both banks! Capacity/5 should be the maximum size for the alternator or charging device (shore power/genny).

We charge our house bank first via a BEP dual sensing VSR, We also take the windlass from the large house bank so the starter battery draws very little power. When the house is at 13.6v for 10 mins the VCR closes and starter battery is charged.

We also have a 5 watt solar panel that just charges the starter battery, which only needs 1 to 2 Ah to recharge. The problem is that this can lead to "chatter" of the relay - when it reaches 13.6 volts the VSR senses the starter battery as being the charge source and it turns on. So a 5 watt solar panel is then trying to charge the depleted house bank, the voltage quickly falls so the relay turns off. This on/off cycle is then repeated, so we turn off the VSR most of the time, but it does have an emergency parallel function if the starter battery gets low.

The SmartBank system mention about is an intelligent electronic relay that overcomes all these problems.

 

[pvb]

If you are fitting the 90 Amp alternator as a second alternator then you will fry both banks! Capacity/5 should be the maximum size for the alternator or charging device (shore power/genny).

This is both incorrect and unnecessary scare-mongering! Batteries accept charging current according to their own requirements, regardless of the size of the alternator. He could fit a 200A alternator without any risk to the batteries.

 

[boatmike]

But Smartbank is essentially only a parallelling relay, which means that both the start and domestic batteries will be subjected to the same voltage.

No because it senses on both batteries and as soon as the engine battery is fully charged it will disconnect.

 

[Jassira]

To prioritise the starter battery, you need a VSR which will bring that battery up to fully charged state before switching to the house battery (unless you are American when you will have it connected the other way round!) The VSR solution is much better in my view as it means the starter battery is always fully charged.

I have a VSR fitted that connects the two battery banks when the house battery voltage reaches the set voltage, and I'm not even an American

I have a 24v system with a pair of 90ah engine and 4 x 135ah house batteries. Generally the engine batteries are charged by the engine and the house batteries are charged by a AirX wind generator. When the house batteries are fully charged the VSR cuts in and tops up the engine batteries.

I did initially connect the VSR the other way round but found that if the house batteries where low, connecting the two banks (VSR connected) caused the voltage in the engine batteries to drop sufficiently to cause the VSR to disconnect, then the voltage increases until the VSR connects, then voltage drops and disconnects, and on it goes, bouncing in and out.

Currently the only way I have of charging my house batteries from the engine involves a set of jump leads, I am planning on changing that, but not yet decided on the best way.

Something to consider:
Saturday morning your on board, you've been plugged in to shore power all week, battery charger has done its work and both sets of batteries are full, the VSR will be connected. You plan to to start the engine and let it warm up whilst you make ready for sea. If the engine doesn't start well and/or you have a duff engine battery, the charger connected to your house batteries could cause your VSR to remain connected long enough to draw starting current through the VSR which was never mean't to carry that current, and that wouldn't be good. Short of a relay/solenoid that disconnects the VSR when shore power is connected I don't have an answer to the problem. I could of course, be searching for a solution to a problem that doesn't exist, wouldn't be the first time .

 

[boatmike]

This is both incorrect and unnecessary scare-mongering! Batteries accept charging current according to their own requirements, regardless of the size of the alternator. He could fit a 200A alternator without any risk to the batteries.

Totally agree.

What I forgot to say earlier though is a relay (smartbank or otherwise) will be kinder to the alternator too because it will probably need to deliver current at up to 1 volt higher with a diode system (actually the resistance varies considerably with current) but the smartbank solution actually maximises the performance of the system and allows the alternator to run at a lower output voltage.

 

[boatmike]

I have a VSR fitted that connects the two battery banks when the house battery voltage reaches the set voltage, and I'm not even an American

I have a 24v system with a pair of 90ah engine and 4 x 135ah house batteries. Generally the engine batteries are charged by the engine and the house batteries are charged by a AirX wind generator. When the house batteries are fully charged the VSR cuts in and tops up the engine batteries.

I did initially connect the VSR the other way round but found that if the house batteries where low, connecting the two banks (VSR connected) caused the voltage in the engine batteries to drop sufficiently to cause the VSR to disconnect, then the voltage increases until the VSR connects, then voltage drops and disconnects, and on it goes, bouncing in and out.

Currently the only way I have of charging my house batteries from the engine involves a set of jump leads, I am planning on changing that, but not yet decided on the best way.

Something to consider:
Saturday morning your on board, you've been plugged in to shore power all week, battery charger has done its work and both sets of batteries are full, the VSR will be connected. You plan to to start the engine and let it warm up whilst you make ready for sea. If the engine doesn't start well and/or you have a duff engine battery, the charger connected to your house batteries could cause your VSR to remain connected long enough to draw starting current through the VSR which was never mean't to carry that current, and that wouldn't be good. Short of a relay/solenoid that disconnects the VSR when shore power is connected I don't have an answer to the problem. I could of course, be searching for a solution to a problem that doesn't exist, wouldn't be the first time .

Again I suggest you read the technical explanation on the smartbank site. You are indeed searching for a problem that wouldnt exist with intelligent control of a relay. It doesnt matter where the charge comes from.

 

[ghostlymoron]

Pity, you started off well, but then fell into the same trap. A VSR does not prioritise either battery, all is does is short them together if there is charging voltage available - just like a pair of diodes does. But unlike diodes, there is no voltage drop. Connecting it "the other way around" also makes no difference, other than selecting which battery is always connected to the alternator, and which is switched.

Nigel, thanks for your patronising response. But you are wrong - see response from Relax 'The VSR I have fitted (sorry can't remember the make) is battery sensed - it only switches in the 'secondary' battery bank, the house bank in my case, when it senses a voltage of (I think) 13.8 and then disconnects when this goes down to something like 13.4.

Its actually a motorised switch with a time delay which prevents fluttering, rather than a relay as such. '

He correctly describes the operation of a VSR as does this extract from BEP website 'The Voltage Sensitive Relay (VSR) allows two batteries to be charged at the same time. When the engine is started and the start battery reaches 13.7 volts, the VSR engages, allowing two battery banks (start and house) to be charged simultaneously. When the voltage drops below 12.8 volts (eg the engine is stopped), the VSR disengages, separating the batteries. This system eliminates the possibility of draining the start battery and protects sensitive electronic equipment powered from the house battery from harmful engine start up spikes.'

 

[pvb]

No because it senses on both batteries and as soon as the engine battery is fully charged it will disconnect.

Really? I don't think so. It doesn't seem to say that anywhere on the Smartbank website. Can you tell me where I can find this information?

 

[sailinglegend420]

This is both incorrect and unnecessary scare-mongering! Batteries accept charging current according to their own requirements, regardless of the size of the alternator. He could fit a 200A alternator without any risk to the batteries.

I'm afraid pvb and Boatmike you are both wrong about the size of the alternator - others have made the same mistake on these forums and been corrected by me and by others.

This a very complex subject - try this site for more info.

http://www.windsun.com/Batteries/Battery_FAQ.htm

I quote:

"Battery Charging Voltages and Currents:

Most flooded batteries should be charged at no more than the "C/8" rate for any sustained period. "C/8" is the battery capacity at the 20-hour rate divided by 8. For a 220 AH battery, this would equal 26 Amps. Gelled cells should be charged at no more than the C/20 rate, or 5% of their amp-hour capacity. The Concorde AGM batteries are a special case - the can be charged at up the the Cx4 rate, or 400% of the capacity for the bulk charge cycle. However, since very few battery cables can take that much current, we don't recommend you try this at home. To avoid cable overheating, you should stick to C/4 or less."


I have a 100 amp alternator which will start to charge happily at 80 amps + another 10 amps or more going to instruments etc. If I stop the engine well before the voltage rises to 14.2v and charge the batterries with my 14.2 volt FP 4HP diesel generator the charging current can go up to 280 amps - so the current is a function of the charging source.

My alternator is always working flat out until it reaches 14.2 volts when the current starts to fall away. My generator goes to 14.2 volts immediately which is why it can deliver more current.

I suspect most standard alternators without a smart controller cannot deliver a high current and a high voltage because they don't have the wattage (VOLTS x AMPS) needed to overcharge most batteries. Also the rated current of an alternator is very different to its real output at temperature. Cable sizing and poor connections will also limit the current delivered. So in the real world a 30 amp alternator may well be OK with a 100Ah battery. The problem comes with a high power/high current "marine alternator" - Balmar type - which could overcharge a small depleted battery bank. A large shorepower charger could also have the same problem

pvb you were also wrong about SmartBank but someone has already corrected you on that one.

Maybe you should limit your comments to the Lounge where you can be critical, I object to your comments here of "unnecessary scare-mongering" when you are not knowledgeable on the subject. Maybe you should add some information on your profile so we can decide whether to take any of your comments on PBO seriously.

 

[pvb]

I'm afraid pvb and Boatmike you are both wrong about the size of the alternator - others have made the same mistake on these forums and been corrected by me and by others.

No, I'm not wrong. It's correct to say that ordinary lead-acid batteries determine how much current can be taken at a given charging voltage, irrespective of the source of the charge.

In the example you gave, it's possible that your batteries might have been able to take more current than your 100A alternator can deliver, which is why you say you had 280A charging current with your generator.

pvb you were also wrong about SmartBank but someone has already corrected you on that one.

No, I wasn't wrong about Smartbank, it is essentially a parallelling relay. In Boatmike's "correction", he claims that Smartbank separates the batteries when the engine battery is fully charged. There's no support for this theory in Smartbank's website.

Maybe you should limit your comments to the Lounge where you can be critical, I object to your comments here of "unnecessary scare-mongering" when you are not knowledgeable on the subject. Maybe you should add some information on your profile so we can decide whether to take any of your comments on PBO seriously.

What a strange comment. The problem is that there's a lot of misunderstanding about charging issues. You've misunderstood, as many others do. As for my technical contributions here, I can only say that many people have been grateful. As for my profile, it's meaningless - I could put anything there and you'd never know whether it was true or not.

And, if I might say it, your signature is very appropriate.