Battery question

S2Jimlad

S2Jimlad

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This may seem really noddy, but I don't have much experience electrically.
I've been given 2 batteries. Gel filled, sealed. They are aviation batteries, designed for light aircraft. They're 12v (and red in colour if that makes any difference!).
Trouble is I don't know what their Ah rating is, therefore if they'll be worth installing. Is it simply a case of hooking up a known load and measuring voltage drop over a given time? Or is there an easier method?
Incidentally, I only intend to run a VHF, 12v socket for a GPS,nav lights and occasionally a tillerpilot.
Thanks.
 
Yes your method of testing would give you the answer you want. If you're not going to use them for starting an engine how long they last is your only worry.
Generally there would be a number of some description written on the battery which if not indicative of the rating may give you the opportunity to google the rating, but doing your load test will give you a clearer idea of whether they can still take the load being as they are second hand.
 
Why don't you test them? Put a known load on them - say 20w bulb - and time it until the voltage drops to around 11.8V-12V which is about as low as you probably want them to discharge. So every hours use gives you 1.66Ah useful capacity.

Possibly weigh them too, as richardbeatie says capacity related to size - and compare with Red Flash batteries ( not red in colour though)
http://www.dmstech.co.uk/marine/pdf/redflashdata.pdf
 
The batteries you speak of are typical of a light aircraft battery. Their primary job is to start the engine and might typically be rated at 40 amp hours. There are different sizes used but usually about 30 to45 AH. They need the capacity for emergency in case of gen failure.
I might suggest that that is all you need to know.
Use them one at a time at least initially and see if they do the job you want then you will know but basically go for it. You will soon know if they are no good or not suitable but I doubt the latter. olewill
 
The "I was given" is the best bit. Use them, you loose nothing.

I used a £70 75 amp leisure battery on a 2 week cruise, just running a VHF, it ran out after 9 days. I didn't have VHF the year before so it was no problem. I did have a charging circuit fitted to the outboard and that does enough to keep a charge for the VHF.

I don't have any lights though.
 
Can you put a photo on a website or PM me one and accurate dimensions and I can probably identify. Fisrt gess is http://www.tayna.co.uk/SBS30-P149.html (I used to work for company making them). Brilliant starting batteries (unless you have a slow to start one like my Volvo 2002) but not good for lighting etc
Mike
 
Hi,
Almost identical to the picture in the link. The raised portion on top of mine is straight across. dimensions:
Length-250mm
Width-93mm
Height-146mm
Weight 8.6Kg (both weigh exactly this)
Thread size M6 Colour -Red
No other marks or features
 
I'm still betting on SBS30 although your dimensions seem slightly odd and weight a bit low. There's a good description at http://www.aerobatteries.com/index.php?main_page=page&id=1&chapter=0still. A photo would help. Do you know their age and history?
Capacity in normal car battery rating terms i.e. 20hr discharge is 30Ah, very small for standby power applications, it's a misuse of them. These batteries are optimised for engine starting and if they are in good nick you could get 1000A from them for a short time, more than the biggest truck battery. They were developed for military jet engine starting. They were developed in UK but company ended up sold to Enersys in USA.
You must be careful cahrging them, a simple unregulated car battery charger will ruin them quickly. Don't go above 13.8V if float charging for long periods. You could use 14.4v for quicker charging up to about 24 hours. If you get near 15V you'll lose water rapidly and you can't replace it.
They aren't gel, they are valve regulated absorbent glass mat type.
Mike
 
They are brand new. They are used in Grobb Tutors. They mount 2 of them in a larger casing and when 1 of those is u/s they have to skip both(crazy, I know). I've got 2 of the serviceable ones.

If what you say is true, would I be better flogging them and buying one more appropriate?
 
OK, that makes sense. I'm sure the standard Grob that the Tutor is based on has a 12V system but it would be typical MoD to insist on upping it and using the same 24V pack as used in Harrier etc! Those used to cost about £500 each on our MoD contracts. If the monoblocs have come out of those batteries that's why they are unlabelled.
The SBS30 is a industrial use version downspecified in some details that don't matter here.
Why do you say these are new? Any new batteries with a duff bloc in should go back to manufacturer for investigation. They are 100% tested before issue. These are more likely used ones which have failed an 80% capacity discharge test. The low weight is also a concern possibly indicating an excessive charging regime. Just because it's RAF (or a civilian contractor) don't assume everything is always done correctly.
You can try a capacity test. A 21W car bulb will take an average of around 1.75 amps which should give you about 16 hours to an end voltage of about 10.2V with a good battery. If you only get about 12-13 hours then it's end of life by aircraft spec. No reason not to use it if it's enough for you but it may not last much longer.
Don't try and check the short circuit current - no normal car type tester can cope with it.
Mike
 
Mike,
Many thanks for your advice. It's been extremely useful. I'll test them as you suggest and probably give them a try. The longest I'll realistically spend onboard my wee boat is 4 or 5 days max, and at night (atmospheric oil lamps!)I don't use electrics anyway unless at sea of course.
I'll post on here how they perform, in case anyone is interested.

Thanks again,
Jim.
 
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