Lead Acid Battery Safe?

pvb said:
A simple fuse fixes that risk.
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OK for domestic batteries where total load may be only 20-30 amps max. But what rating fuse do you put in the starter battery circuit ?

200 amp? = potentially 2.4 Kw of localised heat in a short-circuit before the fuse reaches it's rating.
500 amp? = 6 Kw
 
jwilson said:
OK for domestic batteries where total load may be only 20-30 amps max. But what rating fuse do you put in the starter battery circuit ?

200 amp? = potentially 2.4 Kw of localised heat in a short-circuit before the fuse reaches it's rating.
500 amp? = 6 Kw
Click to expand...

A 250A or 300A MegaFuse will protect the wiring adequately on most small yacht engines.
 
jwilson said:
OK for domestic batteries where total load may be only 20-30 amps max. But what rating fuse do you put in the starter battery circuit ?

200 amp? = potentially 2.4 Kw of localised heat in a short-circuit before the fuse reaches it's rating.
500 amp? = 6 Kw
Click to expand...
Well, yes and no....
If you have a complete short then the load (and heat) is spread all along the cable, which provided it is properly rated can carry at least the expected load current and therefore the fuse rupture current.
If you have a partial short, then yes virtually all the heat is in one spot which is most likely to become either open circuit or total short at such power.
In the unfortuneate circmstance where there is a fault that is a partial short that remains so, then yes you have a fire, but no simple protection device can help in that situation. So fuses do work, fuses do protect cable, equipment and batteries, not in all cases, but certainly in some.
 
Dougal Tolan said:
Well, yes and no....
If you have a complete short then the load (and heat) is spread all along the cable, which provided it is properly rated can carry at least the expected load current and therefore the fuse rupture current.
If you have a partial short, then yes virtually all the heat is in one spot which is most likely to become either open circuit or total short at such power.
In the unfortuneate circmstance where there is a fault that is a partial short that remains so, then yes you have a fire, but no simple protection device can help in that situation. So fuses do work, fuses do protect cable, equipment and batteries, not in all cases, but certainly in some.
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I agree with this. I still do not like the idea of a fuse in the starter circuit: on a really cold day I'd rather the starter cranked rather than a fuse blew, and if you fuse at a rating above the absolute worst-case amperage for the starter motor it's not really going to give much protection if there is a localised "hotspot" in the circuit.
 
Three simple actions:

1. Put a vent in the locker case, I have one at the top of one of the sides, just below the cushions. If you can't fit a decent sized vent then the batteries shouldn't be in there.
2. Fit a 150 amp mega fuse very soon after the positive cable leaves the bank, a catastrophic short will blow that, regular use won't get anywhere near 150 amps!
3. Ensure your charger has a temperature sensor to disconnect charging if the batteries are over temp or fit a cheap temp alarm.

Then leave and forget, you're covered.
 
jwilson said:
I agree with this. I still do not like the idea of a fuse in the starter circuit: on a really cold day I'd rather the starter cranked rather than a fuse blew, and if you fuse at a rating above the absolute worst-case amperage for the starter motor it's not really going to give much protection if there is a localised "hotspot" in the circuit.
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The fuse is to protect the cable, which can handle far greater current than the starter motor will ever demand.
 
kocha44 said:
Are there any preferred brands I have to look out for... I see Amazon offers fairly priced numax 110ah...

Thanks...
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Trojan, Banner and Varta make true leisure batteries, the rest are mostly re-badged standard batteries. Conforming to EN 50342 helps confirm if they are leisure batteries which Banner and Varta do.
 
pvb said:
The fuse is to protect the cable, which can handle far greater current than the starter motor will ever demand.
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Yes, but something connected to the cable, or perhaps a damaged/weakened section of the cable itself could have a slightly higher resistance than a dead short but still pull though enough current to generate 150x12 =1.8 Kw of heat which is quite enough to cause a fire if next to something flammable.

I'm not suggesting not fusing the main battery feed to domestic circuits (can't hurt) but tens of thousands of production boats are sailing around with no battery-line fuses, only individual circuit fuses or circuit-breakers.

Going back to the original question, yes, batteries emit hydrogen and oxygen, but both disperse fairly fast unless the battery box is truly sealed. Some boats (eg HRs) have dedicated vent pipes, but mostly a couple of holes in the surrounding joinery of the battery box is adequate.
 
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Hmmm, two cases reported in yachting monthly over the last year of battery boxes exploding would suggest otherwise. One was a yacht going bluewater and the insurance refused to pay out thinking it was deliberate - it clearly wasn't.
 
The real danger isn't really hydrogen that can somehow be predicted and controlled, but rather runaway charging that happens unexpectedly. I believe now that the safest batteries are Lead Acid. AGM batteries can be subject to runaway charge/heating cycles until inevitably they catch fire. It is important that a temperature sensor is fitted on top of the batteries to tell the charger to stop charging when the temperature is above the limit. As I understand the worst can happen to Lead Acid is that the solution boils away until there is no longer any current flowing. With AGM there is no liquid and thus no chance to break the circuit with overheat.

Good chargers like mastervolt have an optional external temperature sensor. The trouble is that they take only ONE sensor and instead we charge at least two batteries, often more, so only one battery at a time can be monitored.

Did I experience runaway batteries? Yes
Which batteries? YUASA 12V
Fitted where? My home computer Uninterruptible Power Supply
How many times? TWICE in 4 years, always in the summer when the room gets hot
Was it scary? YES IT WAS, woke up in the morning with great stink of sulfur and UPS impossible to touch due to heat. Plastic cover melted. Batteries case melted.

What if I was not at home?
What if the batteries where fitted to the boat?

I have since fitted temperature sensors for the solar charger and the mastervolt charger. But as I said, only one for all the batteries.

Also I use only lead acid batteries since. Not AGM.
 
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If a battery gasses, it produces hydrogen. This is lighter than air - it is the lightest gas. It also has very small molecules, so it diffuses very rapidly - hydrogen balloons will only hold hydrogen for a short time before it diffuses through the envelope; one of the main problems with developing a hydrogen powered car is creating a fuel tank capable of storing it for more than a few hours! Hydrogen is not toxic, but of course is seriously inflammable. However, there is little chance of hydrogen building up in the average battery box, as long as the lid has some kind of hole in it - on mine, it's a finger hole to allow the lid to be lifted! Once out of the battery box it will rapidly be lost by ordinary cabin ventilation; unlike butane, propane or petrol fumes it won't settle into the bilges.

A more realistic concern would be if salt water got into the battery box, when electrolysis could produce chlorine - a real hazard on WW2 submarines, I understand. Chlorine is, of course, seriously poisonous and heavier than air.
 
I once rather stupidly blew up a battery. I can't remember whether it was a "sealed" battery with a single vent or conventional old style car battery. I had started using an angle grinder on a piece of metal on my work bench in the garage, totally forgetting I had a battery on charge sitting on the same bench. I'm not sure if a spark fell directly on the vent or just near it but I and the entire garage were covered in sulphuric acid. Luckily I wasn't hid by and flying bits of battery and had eye protection on for the grinding. Fortunately my garage is attached to the house and we had a shower on the ground floor next to the garage. I stripped off and got straight under the shower preventing any burns. The garage was a complete mess. Everything was dripping acid. I ended up drenching everything with the garden hose. I was very lucky to escape uninjured and often wonder if a spark from connecting a lead to or from a battery could have the same affect.
 
VicS said:
I knew I had a diagram somewhere ... found it

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Actually a good idea to connect the positive lead to one of the pair and the negative lead to the other

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But you don't need to increase the capacity of the starter battery do you? Would you not do better putting all the extra capacity in the domestic bank?
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Really like this one, thank you, will keep it handy.
 
Regarding fuse in the start circuit of a boat. Of course if regulations require then you have to have a fuse. However generally they are not fitted.
First question is the likely hood of a short circuit of the cable. Short cables well insulated and fixed against vibration can minimise the chances. Cars generally dont have a fuse in this circuit despite being in a metal body connected to negative. Compared to our usually GRP (insulating) boat.
A short circuit type failure in the starter or solenoid is not common.
Second question is can the starter battery provide enough power to cause a shorted cable to get red hot? The answer may be be no. Especially if you use a small engine start battery and not paralleled large capacity batteries.
Third question is what would happen if the starter cable did get red hot. Is it mounted against anything that will burn? You can miniise this danger by clamping the cable away from GRP and keeping it short.
If after considering these factors you want a fuse well do so becauae it is your peace of mind that matters. olewill
 
kocha44 said:
Good evening,

I probably have what many would consider a newbie question, but I could not find any clear answers in the other posts on the YBW forum site.

We currently have 2 lead-acid batteries installed under our main lounge seating, 1 for the engine and 1 for leisure. I am looking at adding a couple more batteries in series. So far, the existing ones are working like a charm, but the question remains, are they safe? Do lead-acid batteries not emit fumes or do they pose a potential health hazard, especially for the ones nearest to the batteries at night? Would it therefore be better to have AGM or gel batteries or is simply an urban myth? Are they to be put in a separate box or should I put them in the area in the cockpit area under my outside seat area?

Any advice would be much appreciated.

Thank you in advance.
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Ask yourself. How long have the batteries been in that position? Has there been a problem previously? If you are worried why not connect a small Computer type fan to vent the space, outside the cabin. As others have said make sure you don't over charge. Also why do you want to connect more batteries in series? Do you mean Parallel? Series adds the voltage.( Two 12volt = 24volt) Parallel adds the capacity (Two 100 ahr = 200ahr )
 
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