olygene
olympia wa
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I want to manually charge the two 12volt Class C coach batteries. They are hooked in parallel of course. I will be using a Schumacher 1.5amp charger with float and intend to charge for 72 hours as the batteries are totally drained. I will measure voltage every 12 hours.
I have two questions before I start:
1. Do I have to have the coach battery disconnect switch On or Off?
2. Can I attach the charger's positive lead to the positive terminal on one battery and the negative lead to the negative terminal on the second battery or do I have to charge each battery separately.
Any input would be appreciated as I am sure I have probably forgotten something. Thanks.
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mdfenley
Winder, Georgia
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Fishinghat
Western Washington, USA
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"Connecting the charger's positive lead to the positive terminal on one battery and the negative lead to the negative terminal on the second battery" is the corrrect procedure. That will charge both batteries equally. You should leave the battery switch off.
I'd be very surprised if a 1.5 amp charger would charge up even a single discharged battery, much less two. That size of charger is intended to maintain a battery that had been completely charged up.
I would recommend spending some money on a regular battery charger, one that's deigned for charge a dead or almost dead battery. Check out Harbor Freight. If you can't find an outlet in Olympia, I know they just opened a store in Federal Way. Another possibility would be Costco, but I can't recall seeing a charger there recently. Goog luck.
Holiday Rambler Navigator DP, Hummer, and Honda VT1100C Shadow
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olygene
olympia wa
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OK...viewed the film and it shows I can charge either way.
But it did not show whether the coach battery disconnect switch has to be ON or OFF. Or maybe it doesn't make a difference. I know that charging the coach batteries with the alternator or electric power requires the switch to be ON but I am lost when charging manually. I am concerned about any parasitic drain by leaving the switch ON especially when charging at only 1.5amps.
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Cedarhill
Deep South
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You need to have the switch between the coach and batteries off. A 1.5A charger is very small indeed and you don't need to have part of the meager charging current diverted to parasitic loads in the coach. Even at that, it is going to take every bit of 72 hours and then some to charge those batteries if they are close to flat.
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olygene
olympia wa
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mdfenley and fishinghat: thanks for the comments. Instead of the Schumacher 2amp charger I also have a NAPA 10amp Automatic Deep Cycle battery charger available. I just thought that a trickle charge would be more efficient for fully discharged batteries. I guess I'l' use the 10amp and check the voltage every 4 to 5 hours to see the voltage levels. Thanks again.
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pianotuna
Regina, SK, Canada
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Hi,
168 hours would be better. This is what is balanced and best for twin twelve volt batteries.
As it often doesn't cost a dime more to do this, I think it is worth the trouble.
If you wish to understand the "why" surf here:
correctly interconnecting multiple twelve volt batteries
Regards, Don
Kustom Koach Class C 28'5" 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.
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wa8yxm
Wherever I happen to park
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Switch (Disconnect switch) off, Double or Triple your charge time if they are totally down.
Some figures,, these are at the 20 hour rate.
A group 24 is about 75 amp hours
A group 27 is like 90-95
A group 29 is 100-105
A group 31 is around 120 as I recall (110-120)
You have two so double that
Divide by 1.5 and that is the theroterical minimum hours needed.
Practice you will need to add another 10 percent to that (multiply by 1.1)
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
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Cedarhill
Deep South
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I just read the Smart Gauge link with a critical eye and found either flaws or gaps in the author's information. While I agree with his advice to try to equalize the connections, I don't believe a minor failure to do so will result in the dramatic difference in individual battery life he predicts. He talks about complex calculations and using circuit simulation but he has oversimplified the system with certain assumptions. He assumes that the internal resistance of each battery is a constant that is unrelated to state of charge. I don't believe that is a correct assumption. He also apparently neglects to account for the fact that the batteries delivering the most current initially will experience a more rapid decline in voltage than the batteries delivering less current. These details matter.
If you look at the problem from an energy budget standpoint, I don't see how there can possibly be a big difference in the loading of the various individual batteries. They all start at a know fully charged voltage with a certain finite and near identical level of stored energy. At some later point in time, all the batteries will have a lower voltage due to discharging and that voltage will be essentially the same because they are tied together through a very, very low resistance path. This voltage drop is directly related to the state of charge and surrender of power from the individual batteries. With the exception of the tiny difference accounted for by the Peukert's law, that energy level surrendered by the identical batteries and their state of charge must be almost the same.
I am more than willing to accept that I am wrong and get an education on the subject but it is going to take more than the meager information offered by the Smart Gauge guy to convince me.
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pianotuna
Regina, SK, Canada
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Hi Cedarhill,
The math apparently is correct.
Would you care to offer a better way to connect batteries together?
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