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jestal · 09-01-2017, 06:06 PM

Out of the "inverter R&R" thread I did learn one thing that is completely contrary to all my earlier experience and my be rather important to consider.

Disconnect the Positive terminal first.

Connect the Positive terminal last.

Straight from Magnum and repeated several times in the many conversations I had with them. Questioned and reinforced emphatically. Repeated to me by the tech that did the inverter R&R. The house batteries are dusty like usual except for the Positive post where it was disconnected.

Like most people i have ALWAYS disconnected the negative battery terminal first and connected the negative last for safety. Not so for the inverters and probably for the house batteries under some conditions.

Apparently, Magnum inverters (and other things in the coach...??) may not like this. With a negative ground architecture and many ground paths available if you disconnect the negative terminal first the inverter (or???) will try to find a ground if the positive battery power is still there, and will likely do just that thru the most sensitive electronic circuit and destroy it. Based on this I would tend to think the same applies to the house battery bank since it is hardwired directly to the inverters and the inverters are powered by the battery bank full time.

Just thought I would mention this tidbit. I'm Sure it will spark some conversation which is always good. The concept sure made me think about it. Makes sense in many ways. More hazardous for sure.

But, there is a kernal of truth in there somewhere as in the automotive world the electrical and electronic circuits and systems and devices are spec'd to accept either connection sequence with no damage......just as most of the stuff is spec'd to be protected from a reversed connection.

Any prior knowledge on this I missed?

vsheetz · 09-01-2017, 07:41 PM

I'm a positive guy...

**JohnRR** · 09-03-2017, 12:06 PM

Interesting I've always worked under the thought of negative disconnected first and reconnected last.

jestal · 09-03-2017, 01:40 PM

Yep, same here. That is why the admonishment from Magnum to disconnect positive first and connect positive last was a bit of a surprise. Wondered if anyone knew something I did not or if anyone had heard this before. In any case it may prevent someone from ruining or damaging electrics if they know.

Quote:

Originally Posted by JohnRR

Interesting I've always worked under the thought of negative disconnected first and reconnected last.

757driver · 09-03-2017, 03:37 PM

Quote:

Originally Posted by jestal

Yep, same here. That is why the admonishment from Magnum to disconnect positive first and connect positive last was a bit of a surprise. Wondered if anyone knew something I did not or if anyone had heard this before. In any case it may prevent someone from ruining or damaging electrics if they know.

Had not heard of this before but good to know. With a previous motor home I took the flooded batteries out each winter and stored them at home. With each disconnect and reconnect at the inverter I always did negative first off and last on without any problems in 10 years so associated risks and problems seem rare, but why tempt fate.

MoHoGo · 09-03-2017, 06:14 PM

On the 2017's with the battery disconnect switch, do the batteries go to the disconnect switch and then to the inverters?

757driver · 09-04-2017, 10:48 AM

Quote:

Originally Posted by MoHoGo

On the 2017's with the battery disconnect switch, do the batteries go to the disconnect switch and then to the inverters?

Yes. From the battery positive terminal to the class T fuse then to the disconnect switch then to the inverter.

jestal · 09-04-2017, 11:47 AM

Interesting that the positive side is the chosen factory disconnect. I had wondered about that earlier and forgot to ask. That does agree with Magnum's requirements. Maybe there is more to it with the latest and greatest electronics regarding order of polarity.

Some new twist to watch for. I wonder if the Spartan Control Unit might have a similar polarity sensitivity since it was disconnected negative first and connected negative last (on an earlier service call) and I later determined the fog lights would not work due to a failed SCU.........

MxChief66-1 · 09-04-2017, 01:34 PM

I wonder if it would be an issue removing negative first if I have no shore present, shut down 12volt with switch, powered down Inverters from remote and shut off breakers. I did this before shop disconnected batteries prior to welding for my hydralift install. I'm pretty certain they disconnected - first on both sets of batteries. Huhhh!!

waterboy10 · 09-05-2017, 11:14 AM

I installed a battery disconnect on our 16 Anthem house batteries. PJ told me to install at the positive side of the battery. It works just fine and my house batteries stay up a very long time.

jestal · 09-05-2017, 08:58 PM

Sounds like this is leaning toward disconnect positive first and connect positive last. I'm going to have to tatoo this on my arm to remind me to break an age old habit....