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FreshAir · 09-09-2008, 03:35 PM

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.
Thanks,
Neil

overlander63 · 09-09-2008, 03:40 PM

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.

1953 Flying · 09-09-2008, 04:17 PM

I would also think that this would over charge the batteries and fry the cells.

uwe · 09-09-2008, 05:07 PM

When you say umbilical cord, do you mean the 30A shore power cord, or the trailer to towtruck connector?

Jim & Susan · 09-09-2008, 05:07 PM

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.

Jim

mustang · 09-09-2008, 05:53 PM

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.

FreshAir · 09-09-2008, 06:29 PM

Quote:

Originally Posted by uwe

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.

Jim Clark · 09-09-2008, 06:41 PM

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.

jerrypeterma · 09-09-2008, 06:59 PM

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

overlander63 · 09-09-2008, 07:07 PM

Quote:

Originally Posted by jpeterman

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.

**azflycaster** · 09-09-2008, 07:08 PM

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.

thecatsandi · 09-09-2008, 07:12 PM

Quote:

Originally Posted by Jim Clark

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.

Jim & Susan · 09-09-2008, 07:12 PM

Quote:

Originally Posted by jpeterman

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.

Jim

john hd · 09-09-2008, 07:53 PM

nope

the source with the lowest impeadance will charge the most.

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

john

Jim & Susan · 09-09-2008, 08:22 PM

So does that mean that the regulator in the less powerful charger will shut down the charge function in that charger? Does that mean that using two charing sources is pointless as only one is actually working at any given time? If that's the case, then he should be fine using two sources as only one is actually doing anythng. Am I understanding correclty?

Jim

richinny · 09-09-2008, 08:34 PM

it would seem that only if the to chargers were aiming for the same charging voltage, would the procedure produce more of a charge. as terry said, the one with the higher voltage output would reduce the other.

this sounds like the conversation of hooking two un-phased generators together.

Boondocker · 09-10-2008, 09:08 AM

Quote:

Originally Posted by Jim & Susan

They could easily get too hot and explode, boil dry, etc, etc.

Jim

I'm not a tech head, but thats bad right?

Jim & Susan · 09-10-2008, 09:54 AM

Quote:

Originally Posted by Gen Disarray

I'm not a tech head, but thats bad right?

Normally in this space-time continuum. But like I said, I'm not an engineer.

Jim

mum@home · 09-10-2008, 08:46 PM

Hi,
We do the same thing at power plants for emergency start diesels. The theory is to keep the battery fully charged (topped up), which is done by running the battery chargers all the time. When the diesels run, they have an alternator that will charge the batteries. My guess is that the umbilical cord may be limited to the wire amperage, for example 10 amps. The charger may give an additional 5 amps for a total of 15 amps charging. Thus, charging his trailer batteries quicker.

There is always a small chance of a battery exploding. That is why batteries are encased in boxes with covers. I would recommend hooking up to the battery with the charger, then closing the cover, and finally plugging the charger in last. This way if the battery did explode then the cover would offer some protection, and the person would have the additional 5 feet of clearance when plugging the cord in.

FreshAir · 09-12-2008, 11:00 AM

First thanks for all the information and advice. I was in error in post
#1. Instead of umbilicle it is shore power cord (30 amp) that he is charging through. When I saw him utilizing a auto battery charger from the Honda 2000 at the same time charging through the shore cord I became concerned for safety consideration and asked what??? He is definitely convinced that he is getting very good and a faster charge. Then when he saw the accessory car battery cord for Honda he switched out to that instead of the auto charger. Honda's instruction book states to disconnect the ground cable to use this accessory cord. I believe auto battery charger instructions are similar and when charging a car battery in car I always disconnect the ground. Our friends 2 - 6v batteries are located out of his trailer on the tongue so perhaps that is safer. I am not convinced that his dual charge method is safe or we'd all be doing it.
Neil.