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Thread ID: 31924	2003-04-04 08:33:00	battery charge	BobM (1138)	Press F1

Post ID	Timestamp	Content	User
133300	2003-04-04 08:33:00	I realise this is not a topic for this forum but perhaps you can put me on to the correct site. My question is what is the milliamps that a boat battery could be charged at 24/7/12 to keep it topped up but not damaged due to overcharging. Thanks	BobM (1138)
133301	2003-04-04 08:59:00	Assuming its a standard lead acid marine type, or car type, and there is no load on it at the time, I would go for 30 - 50 mA . Thats about 0 . 7 - 1 . 2 AH per day, which should not cause gassing and loss of electrolyte . I would however suggest an alternative approach of using a constant voltage charger . Set at 13 . 8v it will always keep the battery charged and will not cause any problems . I have had many years of experience in this area, and the longest life of a battery was by use of constant voltage in my experience . You can buy a kit for about $30 that fits in a standard Arlec charger, that achieves the same effect .	godfather (25)
133302	2003-04-04 10:37:00	Thanks godfather, a further question, is it absolutely necessary to diconnect the battery terminals whilst charging at this rate or even at a higher charge rate. say 4amps . I haven't so far but not sure if this is wise or not.	BobM (1138)
133303	2003-04-04 11:57:00	Hi Bob Batteries are interesting and there's lots one can say. No its not absolutely necessary to disconnect a battery when charging at 4 amps. I assume its a relatively low capacity battery (<80ah or so?) if you want to charge at this rate. Generally, a trickle charge of around 1/500 of the ampere hour capacity will keep your battery in good shape without overcharging or losing charge. "Boat battery" is a bit vague. Batteries (lead-acid) generally come in cycle (or "deep cycle") types (rated in ampere hours and usually used for powering appliances etc over reasonably extended periods) or starting batteries (rated in CCA = cold cranking amps or similar, used for turning over engines which requires a lot of amps over a (hopefully) short period). Boat, or marine batteries sometimes are a bit of a combination. Cycle batteries can take a fair bit of discharge without much harm, starting batteries have their life shortened a lot if frequently taken to low charge levels. There's a number of types of battery (flooded, gel, AGM etc.) as well as a lot ofbrands of varying quality. If you want a good site for more info try www.windsun.com which should also give some links to other sites. Cheers	rugila (214)
133304	2003-04-04 12:35:00	To the above I must add that with electricity it's always a good idea to know what one is doing. Quick answers from the internet may not necessarily be in your best interests. Trickle (or maintenance charging) is straightforward enough if you know your battery type and capacity, but for connection and disconnection etc. a good answer would probably require more knowledge of your particular setup. It's unlikely you'll do yourself any (electrical) damage with 12 or 24 volt lead acid batteries, but it is possible you may damage expensive appliances if it's not done right.	rugila (214)
133305	2003-04-05 00:32:00	Thanks Ruqila that is informative site you suggested. The battery is a new Century Marine Pro 500 NS70M CE 13 plate . It is only for recreational use in the boat however on the initial first second of the turnover start, the battery voltage, which is fully charged , drops to 10 volts just for that second and then it turns over easily. The motor is a 1984 Johnston 90 hp. I have had every thing checked, cables renewed and starter reconditioned so thats that That is why, especially as I go out to sea here at Wanganui that the battery be fully charged and ready to go because if it doesn't get past that initial huge draw off I 'm in trouble. The query on the battery diconnection was my concern of damaging the charging module on the engine however I guess if the rectifiers can pass 15 or more amps while charging, the can stop 4 amps (my max. on the home charger) from going back into the boat system.	BobM (1138)
133306	2003-04-05 00:43:00	The difference between marine batteries and car batteries is the extra fibreglass rinforcing in the plate assembly. Quite by accident I discovered that these batteries give a much higher life when sitting on a float charger, than car batteries. It seems that the plate construction actually inhibits the gradual physical decline of the battery. The carry handles are an extra bonus.	godfather (25)
133307	2003-04-05 03:58:00	The voltage drop to 10 V while kicking the starter motor is quite normal . :D The starter motor is basically a dead short until it starts moving, and it takes only a few milliohms of internal resistance in the battery to drop 2-3 V . A constant voltage charger might be OK, but the voltage setting is absolutely critical . If it's too high (and the safe limit depends on temperature, electrolyte concentration, and battery construction) you will ruin the battery in a fairly short time . I'd say that a constant current supply, with a low current limit would be best . But I agree with godfather that constant voltage is better than a continuous trickle . But either should be monitored . I'd prefer to give a boost charge once a week, and not have a chager on all the time . Of course this requires "self discipline" . :D I'm not good at that myself . Charging lead-acid batteries is highly tricky . There are three main stages which must go through to get the battery fully charged . The car batteries never need to be fully charged, because the alternator provides the major loads . So it's a good thing that the car charging system cannot fully charge the battery . :D The same probably applies to a marine system (for a power boat which always run on the engine) . Sailing boats require a totally different system .	Graham L (2)
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