Electrics

[RobsParticipant @robs46138]

Hi, I am coming back to r/c boats after quite a lay off and I have a question about electrics. I will be using a 12 volt motor powered by two 6 volt 4.5 amp/hour batteries. What I would like to know is if I connect them in series to give 12 volts will I still have 4.5 amp/hours or will it double to 9 amp/hours? Also what would be a suitable charger for the batteries? I have a 12 volt 11 amp charger for my car batteries. Would this be suitable and how long should I charge the batteries or should I buy a different charger with a lower charge rate? Sorry if it is a lot of questions but I am working on a limited budget as I only work part time and have to look after my wife who is disabled so I need to keep costs down. Any help will be gratefully appreciated. Cheers, Robs.

[ashley needhamParticipant @ashleyneedham69188]

Robs. Connecting 2x 6v-4.5 a/hr batts to give 12v will still only give you 4.5 Ahrs. DO NOT  use an 11 amo charger on the batteries os they will probly melt!   they need to be charged at a very low rate, say 0.5 amps, so best to get a charger especially for this sort of battery (SLA "gell" cell lead-acid…not a NiMh charger) . A lot of stockists sell one  coping with 6 or 12v for about £12. Maplins do a small plug`n`play charger for 6v batteries only fairly cheaply. Ashley

[RobsParticipant @robs46138]

Hi Ashley, Thanks for prompt answers to my queries. I live not far from the original Maplin store in Southend so I will pay them a visit and get a charger there. Cheers, Robs

[Mike DavidsonParticipant @mikedavidson22772]

 Well said Ashley, What you need Robs is to look at the battery and read the Amp/Hour rating of the device, this gives you the preferred charging rate. Have a look at what people are selling, and look for a Constant Current charger rated at one tenth of the battery A/H rating. I have always worked on a ten hour charge rate. Your batteries are 4,500 mAmpere /hour. and a tenth of that is 450 milliampswhich I say is the ideal rate for a good healthy charge in ten hours. This will not damage your battery, quite the contrary in fact it will do them good. I have an automated charger that discharges thecells in the first cycle, then charges them at a fixed current for ten hours, or until a certainvoltage per cell has been reached, and I have had outstanding service from all my batteries.

          You did ask another question, which was about connecting your batteries or parallel. If you connect in series, each battery contributes its own voltage at the rated ampere /hour current, so your two six volt batteries will give you twelve volts at four and a half Ampere/hours. It id definitely NOT a good idea to connect them in parallel where theoretically, you will get six volts at nine Amp /Hours, because practically, if one cell discharges down to a low level, the remaining cells will try to charge it up, and it has been known for a cell to charge in reverse polaritymuch to the detriment of your poor motor because it won’t get anything like the required voltage to drive it, so do not connect any cells in parallel as it will not give you anything like you expect, and maybe a blown battery into the bargain….Mike     D

[Mike DavidsonParticipant @mikedavidson22772]

Sorry Robs, I missed part of your question, but I note you have an 11 amp car battery charger. As you will recall, I said that your batteries for the boat will need 450 milliampsto charge, and doing a sum on the back of this fag packet, I seethat you have 22 times more than you need. Ashley gave you a clue where the excess charge might go, when he suggested your batteries might melt. It all boils down to internal resistance, and the internal resistance of a car battery goes up as the battery nears full chargeconsequently the current flowing through the batterygets smaller and smallerand reduces to a mere trickleat the finish when the battery is fully chargedIn the battery workshop when I was working on aircraft, the technicians used a hydrometer to measure the specific gravity of the acid in batteries on chargeto determine their charge state, and if your batteries are lead acid type, you could do the same as I believe that the acid rises to a specific gravity of 1275, but DO NOT use your car battery charger,because you could start making some very expensive smoke, but before I finish, welcome back to the world of model boatsI really do hope you have loads of fun,and that your models win lots of prizes

[RobsParticipant @robs46138]

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