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Old 09-09-2008, 04:35 PM   #1
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SHOCKING ... or maybe not

A good friend of Lynn and I was camping with us recently with his 30' SOB. I noticed one morning that he was charging his batteries the normal way through his 'umbilical' cord .....PLUS with a car battery charger connected to his batteries (2 - 6 volts) that was also plugged into his Honda 2000 . Now I know little of the potenial danger that set up may pose. I asked him did that help. He swears (not really swear , a good church guy) that it does. This friend is a retired, well educated doctor (former county med. examiner) and grand dad of many. He camps several times a year for 2 weeks at a time around the west. He explained that his 5 grown kids and multitude of grand children join him frequently and really use up his electric, and water with showers and all. In addition of a solar panel he says the 'dual' charging hook-up to the batteries gives him a quick turn around with his electric supply. In fact he noticed in my tools my car battery charge cord for my Honda. He went and bought one so he won't have to lug his car battery charger around. He was by our home 2 nights ago and during the visit he asked if I tried the 'dual' charge cord system. "No way!" I exclaimed, and said it sounded dangerous. So he challenged me to ask my Airstream friends for an answer. So, Friends, what do you say. I will be sending him a link to your answers.
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Old 09-09-2008, 04:40 PM   #2
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It's not so much dangerous, as wasteful. The more powerful charging system will overpower the other chargers in the system, thus winding up being the only real charger. It is possible to damage the less powerful units in the setup as well. This is why it is not recommended to leave a battery charger on a battery when the car is running.
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Old 09-09-2008, 05:17 PM   #3
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I would also think that this would over charge the batteries and fry the cells.
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Old 09-09-2008, 06:07 PM   #4
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When you say umbilical cord, do you mean the 30A shore power cord, or the trailer to towtruck connector?
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Old 09-09-2008, 06:07 PM   #5
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What Terry and Robert said, plus some other stuff

Multiple charging sources used to charge a series of batteries is nothing new. But there's more to it that simply pumping juice to the batteries. Lemme explain some.

Full disclosure: I'm not an engineer and never played one on TV. I work with DC power at work, but I only help maintain systems, I don't design them. Your mileage may vary. Free advice is worth everything you pay for it.

We have rectifiers at work that are wired together in a big system that supplies DC power to equipment AND charges the battery backup system. We may have, for example, 10 x 200amp rectifiers in one system pushing 1200amps of actual power out to the equipment. There is a computer that monitors the batteries and as needed increases power to charge batteries as needed (maintains a certain charge on the batteries).

The key differences here as I see it, are that the rectifiers share a common buss that feeds the equipment and the battery string(s) and have a common power SOURCE. AND there is a computer that monitors and controls all of this stuff and keep all those electrons in the right places.

Bottom line is that I would NOT try what your friend is doing unless there was a way to monitor what was going on inside those batteries. They could easily get too hot and explode, boil dry, etc, etc.

Just my 2 cents.

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Old 09-09-2008, 06:53 PM   #6
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I am baffled at your freinds logic. One can presume that if all systems are working correct then they cant overcharge because each system is regulated. They would all turn off at each systems preset setting 13.2, 12.8 or 13.6 volts. My only couse for concerne is amps being shoved into the battery at once. I would ask him if he charges a dead battery with the 200 amp start option on his battery charger? If he says no then he has contradicted himself.
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Old 09-09-2008, 07:29 PM   #7
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Quote:
Originally Posted by uwe View Post
When you say umbilical cord, do you mean the 30A shore power cord, or the trailer to towtruck connector?
I'm sorry, I meant the 30 amp shore power cord.
Neil.
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Old 09-09-2008, 07:41 PM   #8
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It is complicated. Volumes of information exist on how to charge batteries, how fast to charge them, how charging shortens their life and so on. I would think using multiple sources would cause problems. I don't think the eu2000i battery charging circuit is regulated.
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Old 09-09-2008, 07:59 PM   #9
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Isn't the number of amps being pushed the only danger. the volts would be the same (12 to 14 or so) but the amps can go up. we use up to 3 jumper cables on our backhoe during the winter. All hooked up with the + to the bat and the - to the frame. App. 14 volts but a increase in amps. Maybe
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Old 09-09-2008, 08:07 PM   #10
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Isn't the number of amps being pushed the only danger. the volts would be the same (12 to 14 or so) but the amps can go up. we use up to 3 jumper cables on our backhoe during the winter. All hooked up with the + to the bat and the - to the frame. App. 14 volts but a increase in amps. Maybe
The way electricity works is kind of like water through a straw. The water level (voltage) tends to seek its own level. The jumper cables and charge lines are like straws through which the electricity (water) flows, the bigger the straw, the faster it flows.
If you add a water pump (generator) on one end of the straw, it will force more water (electricity) into the low end of the lake (battery). If you have more than one water pump, and they don't all put out the same pressure or volume, the one with the highest capacity will do most of the work, and if it is too much higher, it can force the water back up the other straws (jumper cables), and cause the water to overflow.
Hopefully this didn't make things more confusing.
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Old 09-09-2008, 08:08 PM   #11
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If the converter in the trailer is 3 stage, might it not look at the increased voltage from the generator or charger and think the battery is charged more then it is? At that point the converter could shift into float mode. Does not sound practical to me.
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Old 09-09-2008, 08:12 PM   #12
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I would think using multiple sources would cause problems. I don't think the eu2000i battery charging circuit is regulated.
It is not regulated. It is constant voltage. It will keep charging until you turn the generator off.
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Old 09-09-2008, 08:12 PM   #13
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Isn't the number of amps being pushed the only danger. the volts would be the same (12 to 14 or so) but the amps can go up......
That was kinda the point I was trying to make (poorly stated by me). There are two sources pouring electrons into that battery. One source is the tow vehicle, the other the 110v battery charger via the generator. The regulators in each source are not talking to each other. I suppose it's possible that the two charging sources could at some point overwhelm one or the other. Just something else to consider.

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Old 09-09-2008, 08:53 PM   #14
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nope

the source with the lowest impeadance will charge the most.

i.e. the one that can make the most amps will win.

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