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Old 28-02-2013, 17:30   #1
TOM
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Voltage Drop.

Re-Launching Byamee after 8 weeks on the hard we found that we had a 15 amp voltage drop coming out of our 2x 6 volt cranking batteries. We ran all the usual checks ie turning off absolutely everything still minus 15 amps coming out . I disconnected the cranking batteries and reconnected to a small 12 volt battery i use for my dive hooka guess what everything is fine.

Did a hydrometer test on the 6 volt batts and they are basically fried .

My question is can a fried set of batteries have such a huge negative amp draw ? Has anyone else had this problem?

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Byamee after her $2500 usd paint job .Possible the most beautiful steel 40 foot yacht . Well we think so.
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Old 28-02-2013, 19:09   #2
TOM
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Re: Voltage Drop.

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Originally Posted by TOM View Post
Re-Launching Byamee after 8 weeks on the hard we found that we had a 15 amp voltage drop coming out of our 2x 6 volt cranking batteries. We ran all the usual checks ie turning off absolutely everything still minus 15 amps coming out . I disconnected the cranking batteries and reconnected to a small 12 volt battery i use for my dive hooka guess what everything is fine.

Did a hydrometer test on the 6 volt batts and they are basically fried .

My question is can a fried set of batteries have such a huge negative amp draw ? Has anyone else had this problem?

www.byamee.com

Byamee after her $2500 usd paint job .Possible the most beautiful steel 40 foot yacht . Well we think so.

Any info on wheather i should replace my wet cell cranking batts with sealed ones ? I currently have 2x 6 volt truck batts but would like to go to a sealed single 12 volt batt
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Old 28-02-2013, 19:17   #3
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Re: Voltage Drop.

15 amp voltage drop? that makes no sense. You got volts you got amps. Not the same things. What are you checking?
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Old 28-02-2013, 19:40   #4
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Re: Voltage Drop.

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15 amp voltage drop? that makes no sense. You got volts you got amps. Not the same things. What are you checking?
Sorry, you are indeed correct . I have been in the engine room all day and i think the Trinadad humidity has got to me. We are getting a 15 amp draw with everything switched off . It appears to be that the cranking batteries are dead and are sucking amps out off the house batts when the 2 systems are switched on.... hope that makes sence
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Old 28-02-2013, 19:47   #5
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Re: Voltage Drop.

Sounds like maybe a shorted cell or 2? Better get them unconnected. On an aside, I have heard that you could get a fire with a mix of old and newer batteries from that very situation
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Old 28-02-2013, 19:53   #6
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Re: Voltage Drop.

It would be clearer to speak in terms of voltage and voltage drops.

Do the start batteries lose voltage when completely disconnected? Are the house batteries losing voltage when completely disconnected?

How are you measuring current?...with a clamp ammeter or what else?

You basically have to trace this out by removing possibilities from an electrical standpoint. Turn off breakers, turn off switches or pull fuses one by one.
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Old 28-02-2013, 20:43   #7
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Re: Voltage Drop.

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It appears to be that the cranking batteries are dead and are sucking amps out off the house batts when the 2 systems are switched on.... hope that makes sence
Do you have your battery switch turned to the "Both" position? If so, you are putting the crank batteries in parallel with the house bank. If the crank batteries are discharged to a lower voltage, the house bank will try to charge them. If your ammeter shunt is on the negative terminal of the house bank, you should see a negative draw. The size of the current draw will depend on the voltage differential between the two banks.
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Old 01-03-2013, 17:10   #8
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Re: Voltage Drop.

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Do you have your battery switch turned to the "Both" position? If so, you are putting the crank batteries in parallel with the house bank. If the crank batteries are discharged to a lower voltage, the house bank will try to charge them. If your ammeter shunt is on the negative terminal of the house bank, you should see a negative draw. The size of the current draw will depend on the voltage differential between the two banks.
Thanks that makes perfect sence and is indeed what is happening. I replaced my 2 six volt cranking batts with a 12 volt 860 cca batt today. I'm in the process of charging it up . But i guess whenever we are on 1+2 there is always going to be a voltage difference between the two batts.
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Old 02-03-2013, 14:43   #9
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Re: Voltage Drop.

"But i guess whenever we are on 1+2 there is always going to be a voltage difference between the two batts. "
Not always. This is why batteries generalyl should not be combined unless they are very similar. If they are similar they will equalize out fairly soon and then any voltage difference between them ends. If they are different...it will take longer. If it takes VERY long, they shouldn't be combined at all.
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