Yup very confusing! I have a Magnum MS2012 & on page 15 of their instruction it does say disconnect positive battery first. I've worked on my batteries several times & have always disconnected the negative battery cable first! So far no issues. i would think something that important would have a HUGE notice thats clearly visible in the battery compartment stating to to disconnect the positive cable first!
I think there may be some confusion here about what is actually being disconnected. The Battery Bank vs the Inverter. The case of the inverter is suppose to be grounded and can see where disconnecting the negative cable FROM THE INVERTER could cause problems while disconnecting the negative cable FROM THE BATTERY BANK would cut off all sources of return or grounding.
I agree, but the help desk said that disconnecting the negative terminal on the battery first would damage the inverter. I told him I didn’t think that was possible and that’s why I’m waiting for their field engineer to call me back.
When you disconnect the battery negative terminal, the battery is then out of the circuit; the system is powered down. Other devices (loads, chargers) really don't know which battery terminal was opened, the voltage source simply went away. As you stated, that is good practice to avoid an accidental short.
But removing a load connection is a different situation. If the +12 V terminal is live, it stays live regardless of the negative connection. (And you need to insulate the live cable end after carefully disconnecting it.) The problem here is the ground loops Magnum seems to incorporate with their accessories. Just like in audio systems, ground loops through the wiring should be avoided! In this case, with high currents, even normal operation could result in high ground current through the accessory ground connection, due to possible significant voltage drop across the inverter ground path.
That’s cool! As a musician and audio engineer, I’ve enjoyed your audio articles (and more recently your RV articles) for years. As you probably know, the June 1995 issue of the AES Journal offered the definitive explanation of ground loops (I used to hang out with a couple of the authors). Now that EV and Crown have left town, I’m designing products for WFCO!
For me it was at the battery terminal. However the Magnum tech said it didn’t matter if it was at battery or at the inverter it self. Always disconnect the positive first. Never have negative disconnected while positive is still connected.
On our 4th RV, after 2 Fifth Wheels and 1 Class C. I have always disconnected the ground first, but now await Mike's update. Our Micro Minnie uses WFCO WF-895/-AD--GE power converter/distribution panel. I have used the battery disconnect first then the ground from battery and used smart battery maintainer since we keep our unit in the barn defeating the solar use. Winnebago Customer Support didn't have an answer and I have a call in to WFCO tech support. Winnebago is sending me electrical and solar and even plumbing diagrams...since they are still updating their website. I'm so glad Mike is pursuing this. Not sure I have to change my process or not?
I agree with a previous poster, I think we're talking apples and oranges here. I agree with you, d/c the negative from the BATTERY BANK, that takes the entire system down (as long as shore power is likewise d/c'd). But if battery bank is still connected, THEN Magnum may have an issue if negative is back fed thru the remote, meaning d/c the INVERTER while still powered... Let's see what they say! ST
I had a magnum inverter and if I remember correctly the suggested wiring showed a dc breaker was suggested or required. My present victron inverter has a dc fuse and a battery disconnect. Turn the switch and it’s disconnected. And after flipping the battery switch I always disconnect the negative first.
I use Tekton composite rachets: TEKTON 1/2 Inch Drive x 10 Inch Composite Quick-Release Ratchet | 1458 from Amazon. Harbor Freight sells a cheaper version but the sockets won't stay on (not to spec).
An electrician friend suggest using shrink tubing on screw driver shafts and dipping plier handles in Platicraft liquid tape or similar.
OMG. Scary business, both physically and financially. Somehow, I think there needs to be a switch/fuse/breaker on the positive to provide a fail-safe procedure, as well as maybe a placard to remind you to use it when working on the inverter. This also seems like it might be a design oversight the inverter makers might need to attend to.? Regardless, I'm going to read all the fine print that comes with my new inverter.
I suspect that Magnum needs to add an inline fuse in the shield of the communications cable to prevent damage. But I have to talk to engineering first before I can recommend anything.
It's pretty clear from the note that they're talking about disconnecting the inverter negative connection and not the battery negative connection. Obviously if you disconnect the battery negative terminal there's no return path to the battery.
But the help desk specifically said that disconnecting the negative terminal from the battery could damage their inverter. That’s what I have trouble believing…
Unfortunately -- as I'm sure you know -- most companies these days often staff their help desk with people who, through no fault of their own, lack the necessary knowledge and training. I'll be amazed if disconnecting the neg(-) BATTERY terminal first can cause damage. That would be incredibly poor design for such a good company.
Might be worth putting a fuse in the ground lead of the accessory. Since most mechanics will remove the negative post first, that could prevent damage if the inverter tried to source ground through the accessory.
From personal experience, my Magnum inverter control board had to be replaced. Upon calling Magnum, the tech and I could not determine a reason until I told him that when I store the coach, I had disconnected the negative cable while leaving positive connected. This preserved the batteries in storage. He advised to never do that. Instead, disconnect the positive so as not to damage the inverter board. So I installed another disconnect switch to safely do so when storing the coach.
Mike: As an Electrical Engineer I would recommend that anyone who will be installing and uninstalling batteries buy a good set of rated insulated tools. They can be pricey, but one slip with a regular wrench or screwdriver can cost a whole lot more.
True that! Many consumers think that 12-volt RV batteries can’t hurt you because you won’t get shocked. But there are huge currents involved that can cause all sorts of other damage. Plus I’ve witnessed one arc flash up close and personal (from 3 ft away). It was pretty small and only vaporized about 3 ft of 12 gauge wire, but it sure got my attention!
I wish Magnum would give me an inverter so I can try this myself.
Glad I was able to begin getting this sorted out. Please share this post with anyone you know who has a Magnum inverter.
What about turning the the battery disconnect switch off first then disconnecting the battery terminal connections? That is what I always do.
Is your disconnect switch on the positive battery terminal. If so, that should work. But Standby for clarification as soon as I get it.
Disconnect switch is on the positive battery cable.
Just depends how you system is wired, theres NO standard at all!
Snoopy
Yup very confusing! I have a Magnum MS2012 & on page 15 of their instruction it does say disconnect positive battery first. I've worked on my batteries several times & have always disconnected the negative battery cable first! So far no issues. i would think something that important would have a HUGE notice thats clearly visible in the battery compartment stating to to disconnect the positive cable first!
Snoopy
I totally agree. Buried in the inverter manual is less than ideal.
I think there may be some confusion here about what is actually being disconnected. The Battery Bank vs the Inverter. The case of the inverter is suppose to be grounded and can see where disconnecting the negative cable FROM THE INVERTER could cause problems while disconnecting the negative cable FROM THE BATTERY BANK would cut off all sources of return or grounding.
I agree, but the help desk said that disconnecting the negative terminal on the battery first would damage the inverter. I told him I didn’t think that was possible and that’s why I’m waiting for their field engineer to call me back.
When you disconnect the battery negative terminal, the battery is then out of the circuit; the system is powered down. Other devices (loads, chargers) really don't know which battery terminal was opened, the voltage source simply went away. As you stated, that is good practice to avoid an accidental short.
But removing a load connection is a different situation. If the +12 V terminal is live, it stays live regardless of the negative connection. (And you need to insulate the live cable end after carefully disconnecting it.) The problem here is the ground loops Magnum seems to incorporate with their accessories. Just like in audio systems, ground loops through the wiring should be avoided! In this case, with high currents, even normal operation could result in high ground current through the accessory ground connection, due to possible significant voltage drop across the inverter ground path.
Ah yes, spoken like an audio engineer. Read my article on ground loop hum here: https://www.prosoundweb.com/troubleshooting-hum-awe/
That’s cool! As a musician and audio engineer, I’ve enjoyed your audio articles (and more recently your RV articles) for years. As you probably know, the June 1995 issue of the AES Journal offered the definitive explanation of ground loops (I used to hang out with a couple of the authors). Now that EV and Crown have left town, I’m designing products for WFCO!
For me it was at the battery terminal. However the Magnum tech said it didn’t matter if it was at battery or at the inverter it self. Always disconnect the positive first. Never have negative disconnected while positive is still connected.
On our 4th RV, after 2 Fifth Wheels and 1 Class C. I have always disconnected the ground first, but now await Mike's update. Our Micro Minnie uses WFCO WF-895/-AD--GE power converter/distribution panel. I have used the battery disconnect first then the ground from battery and used smart battery maintainer since we keep our unit in the barn defeating the solar use. Winnebago Customer Support didn't have an answer and I have a call in to WFCO tech support. Winnebago is sending me electrical and solar and even plumbing diagrams...since they are still updating their website. I'm so glad Mike is pursuing this. Not sure I have to change my process or not?
Sorry,8955 model
I agree with a previous poster, I think we're talking apples and oranges here. I agree with you, d/c the negative from the BATTERY BANK, that takes the entire system down (as long as shore power is likewise d/c'd). But if battery bank is still connected, THEN Magnum may have an issue if negative is back fed thru the remote, meaning d/c the INVERTER while still powered... Let's see what they say! ST
I had a magnum inverter and if I remember correctly the suggested wiring showed a dc breaker was suggested or required. My present victron inverter has a dc fuse and a battery disconnect. Turn the switch and it’s disconnected. And after flipping the battery switch I always disconnect the negative first.
Yes, it is on the positive battery lead.
I use Tekton composite rachets: TEKTON 1/2 Inch Drive x 10 Inch Composite Quick-Release Ratchet | 1458 from Amazon. Harbor Freight sells a cheaper version but the sockets won't stay on (not to spec).
An electrician friend suggest using shrink tubing on screw driver shafts and dipping plier handles in Platicraft liquid tape or similar.
OMG. Scary business, both physically and financially. Somehow, I think there needs to be a switch/fuse/breaker on the positive to provide a fail-safe procedure, as well as maybe a placard to remind you to use it when working on the inverter. This also seems like it might be a design oversight the inverter makers might need to attend to.? Regardless, I'm going to read all the fine print that comes with my new inverter.
I suspect that Magnum needs to add an inline fuse in the shield of the communications cable to prevent damage. But I have to talk to engineering first before I can recommend anything.
It's pretty clear from the note that they're talking about disconnecting the inverter negative connection and not the battery negative connection. Obviously if you disconnect the battery negative terminal there's no return path to the battery.
But the help desk specifically said that disconnecting the negative terminal from the battery could damage their inverter. That’s what I have trouble believing…
Unfortunately -- as I'm sure you know -- most companies these days often staff their help desk with people who, through no fault of their own, lack the necessary knowledge and training. I'll be amazed if disconnecting the neg(-) BATTERY terminal first can cause damage. That would be incredibly poor design for such a good company.
Agreed... Which is why I want to talk to a field engineer.
Might be worth putting a fuse in the ground lead of the accessory. Since most mechanics will remove the negative post first, that could prevent damage if the inverter tried to source ground through the accessory.
I thought of that as well. That’s one of the things I want to talk to Magnum engineering about.
From personal experience, my Magnum inverter control board had to be replaced. Upon calling Magnum, the tech and I could not determine a reason until I told him that when I store the coach, I had disconnected the negative cable while leaving positive connected. This preserved the batteries in storage. He advised to never do that. Instead, disconnect the positive so as not to damage the inverter board. So I installed another disconnect switch to safely do so when storing the coach.
Hi Tom,
Are you referring to disconnecting the negative at the inverter, or disconnecting the negative battery terminal?
WOW! How about we disconnect the mentioned network line, THEN remove negative first? Head exploding.
That’s what I want to ask a Magnum field engineer. I’ll update once I know more.
Mike: As an Electrical Engineer I would recommend that anyone who will be installing and uninstalling batteries buy a good set of rated insulated tools. They can be pricey, but one slip with a regular wrench or screwdriver can cost a whole lot more.
True that! Many consumers think that 12-volt RV batteries can’t hurt you because you won’t get shocked. But there are huge currents involved that can cause all sorts of other damage. Plus I’ve witnessed one arc flash up close and personal (from 3 ft away). It was pretty small and only vaporized about 3 ft of 12 gauge wire, but it sure got my attention!