So If You Want To Ventilate The Battery Box .......

Our battery box has its original ventilation system from 1980. The battery box is sealed except for a 2" vent pipe that goes up to a dorade box and a centrifugal fan that can be switched on to force air through the box. The fan used to be interlocked to the engine so it could automatically be switched on by the ignition and the shore power battery charger. I don't bother with those interlocks these days. Our batteries are open cell 1000 amp hr
 
sounds like this is more for hydrogen ventilation. My last boat had two passive vent pipes at the top of the batt box leading overboard. On your setup, where does replacement air enter the box?
 
Dave100456 said:
sounds like this is more for hydrogen ventilation. My last boat had two passive vent pipes at the top of the batt box leading overboard. On your setup, where does replacement air enter the box?
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The exhaust pipe is at one end of the box and the fan is installed at the other end. The fan pulls air from the bilges so its quite cool. The system was installed for hydrogen ventilation I am sure but also would work well for heat extraction
 
Dave100456 said:
As I am planning this system I am trying to design out any potential problems. Its good to know your batteries did not get hot. Can you tell me what DoD you took them down to and how many amps you saw when you charged them back up at?
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Never discharged below about 50%. Never saw much more than 70 or 80A charge rate, using a 90A alternator.
 
Dave100456 said:
I do have 660w of PV but have no way of making the sun shine!
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OK. But modern panels will still give you something in cloud. I've got over 1A out of a 100W panel in torrential rain in NI in summer. Often when sailing along in summer a single 100W panel will balance the consumption.

You've clearly got a very big bank - mine is only 360Ah - but 400Ah is a lot of drain - over 8A solid for two full days. If you've 660W of panels on top of that then what on earth are you running to consume so much? Sounds like you might need a dedicated generator.
 
lpdsn said:
OK. But modern panels will still give you something in cloud. I've got over 1A out of a 100W panel in torrential rain in NI in summer. Often when sailing along in summer a single 100W panel will balance the consumption.

You've clearly got a very big bank - mine is only 360Ah - but 400Ah is a lot of drain - over 8A solid for two full days. If you've 660W of panels on top of that then what on earth are you running to consume so much? Sounds like you might need a dedicated generator.
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Its good to hear what you get from PV on overcast days as I've never had 'sophisticated solar', only temporary 30watt panels for combatting battery self discharge when I leave the boat.

Watermaker, heater, freezer and inverter for washing machine all heavy consumers. Trying to do without a genset. Calculations show there's no power issues when moving - hydrogenerator, however, at anchor for 3 overcast days my calculations show batts drain would be around 70% DoD. All is worst case scenario continuing to use consumers without hesitation and whilst I won't make it a habit of it, batts spec shows 1000 cycles at 70% discharge.
 
Seajet said:
I don't have a cooling problem with my battery but did fit a vent tube; as it's hydrogen which is given off,
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No, the gas produced is a mixture of hydrogen and oxygen in stoichiometric proportions, highly explosive if sufficiently concentrated i.e. not diluted with plenty of free air.
 
MartynG said:
I try not to abuse the batteries by discharging them too deeply.
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The subjective definition of abuse in a battery sense has much to do with the capabilities of the battery. Some batts will happily accept 95% discharge and do this 1500 cycles. Taking these batts repeatedly down to a 30% state of charge may not be considered abuse. However, a battery that has a cyclic life of only 300 at 50% depth of discharge may be considered as being abused if it was taken to below 50% repeatedly.
I think my battery spec is 1,000 cycles at 70% depth of discharge (ie 30% state of charge). Whilst I would prefer to have fully charged batts all the time, in the real world of weeks offshore, taking them occasionally to 40% state of charge I wouldnt count as abuse. It really depends on what setup you’ve got and how you use it.
 
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Dave100456 said:
Its good to hear what you get from PV on overcast days as I've never had 'sophisticated solar', only temporary 30watt panels for combatting battery self discharge when I leave the boat.

Watermaker, heater, freezer and inverter for washing machine all heavy consumers. Trying to do without a genset. Calculations show there's no power issues when moving - hydrogenerator, however, at anchor for 3 overcast days my calculations show batts drain would be around 70% DoD. All is worst case scenario continuing to use consumers without hesitation and whilst I won't make it a habit of it, batts spec shows 1000 cycles at 70% discharge.
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No one would call my solar installation spohisticated. It's an el cheapo Amazon 100W panel with a very cheap controller. I bought it to cope with self discharge when overwintering in one particular marina where leaving shorepower connected with minimal usage was extortionate. When sailing it is tied in position wherever is convenient but I do find it useful.

You do have a far heavier drain than I do, but I'm sure there are a few good ideas for mitigating it. Obviously if you're using your engine regularly just to recharge your batteries it's a lot of additional wear and tear on an expensive part of the boat. I guess getting back 400Ah will take a fair few hours of engine running.

Obviously your boat so you'll know what suits you best but I suspect a lot of people in your position and with your usage would have a big solar installation and would have looked seriously at a small diesel generator. Being a bit of a cynic I sometimes joke that these gen sets are sacrificial to protect the engine from unnecessary use.

Not sure where you're based, but it might be interesting to get feedback from PaulRainbow. I believe he has about 300W of panels in East Anglia that cover his liveaboard usage in the summer. I'm guessing you'll have more space on your boat so even if you could get, say, 400W of panels permanent set up. Let's say that gives you 15A for an average 8 hours per day, you should get more in summer, that's still 120Ah per day, so 360Ah over three days, which is quite a chunk of your usage (obviously battery (in)efficiencies mean 360Ah in isn't the same as 360Ah out).
 
Dave100456 said:
I think my battery spec is 1,000 cycles at 70% depth of discharge (ie 30% state of charge). Whilst I would prefer to have fully charged batts all the time, in the real world of weeks offshore, taking them occasionally to 40% state of charge I wouldnt count as abuse. It really depends on what setup you’ve got and how you use it.
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Battery specs are always quoted in optimum conditions, and cycle life will almost certainly be quoted on the basis of controlled discharge immediately followed by very carefully controlled charging. In the real world, this might not be easy to achieve, so cycle life might not be quite as high.
 
In my experience in the Caribbean anybody using a 12v watermaker needs 600-1000w of solar to keep their batteries charged and make water. Those that have less than 600w and dont have energy inefficient items like washing machines or poorly insulated fridges and freezers still need to occationally run their engines to top up the batteries whilst making water. You can deeply cycle your batteries but unless you get them fully charged regularly you will inevitiably shorten their life. Without sufficient solar to meet your demands or a good mains charger running from a generator it is very hard to fully charge your batteries with your use profile.
 
pvb said:
Battery specs are always quoted in optimum conditions, and cycle life will almost certainly be quoted on the basis of controlled discharge immediately followed by very carefully controlled charging. In the real world, this might not be easy to achieve, so cycle life might not be quite as high.
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I agree with you regarding lab specs and reality. I hope to not use them to 70% DoD but if I do so once a month they should last many years; I hope!
 
geem said:
In my experience in the Caribbean anybody using a 12v watermaker needs 600-1000w of solar to keep their batteries charged and make water. Those that have less than 600w and dont have energy inefficient items like washing machines or poorly insulated fridges and freezers still need to occationally run their engines to top up the batteries whilst making water. You can deeply cycle your batteries but unless you get them fully charged regularly you will inevitiably shorten their life. Without sufficient solar to meet your demands or a good mains charger running from a generator it is very hard to fully charge your batteries with your use profile.
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Thanks for the examples of actual cruisers and their PV sizes. It’s good to have reports of actual experiences. I have 660watt fixed PV and controller capacity provision for deploying temporary addition flexible panels at anchor if needed.
 
Plevier said:
No, the gas produced is a mixture of hydrogen and oxygen in stoichiometric proportions, highly explosive if sufficiently concentrated i.e. not diluted with plenty of free air.
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Will an oxygen-hydrogen mixture explode (ie detonate - supersonic propagation, high overpressure)? I thought it would only deflagrate (subsonic propagation, low overpressure) but I could be wrong. I've blown up a balloon full of the stoichiometric mixture loads of times in shows, and that's a deflagration. Still pleasantly loud, though.
 
JumbleDuck said:
Will an oxygen-hydrogen mixture explode (ie detonate - supersonic propagation, high overpressure)? I thought it would only deflagrate (subsonic propagation, low overpressure)
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Still, not the sort of thing you want going on in the battery box under your bunk at 2am.
 
I read somewhere (possibly on this forum) that hydrogen is pretty nippy stuff, and will readily find its way through modest openings and escape from a boat, and hence little in the way of vent openings/tubes was usually required.

Whether that's true I don't know, and given the astonishing sizes of the banks of batteries some of you lug around with you, maybe your into a whole other, more industrial, level of issues.

A thing that has occasionally puzzled me is that if hydrogen is given off during charging, presumably the battery needs to re-absorb hydrogen again when it is being discharged. Is this true? And if so, does the comparative reduction in hydrogen in the remaining air around the batteries have any notable qualities or issues?
 
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