3 12v deep cycle batteries spark bad when last one connected

cookj

So I was hooking 3 12v deep cycle batteries to my golf cart wired in series I was hooking up the last positive to negative when the jumper from the positive post touched the negative post on the last battery all heck broke loose melted the battery crimp on the jumper and sparks flew. I unhooked everything from the golf cart and tried to wire JUST the batteries in series and the same thing happened and all batteries are new and have the same voltage. Am I doing something wrong or bad battery? If bad battery how do I find out which one is the bad one? 

BB.

Welcome to the forum Cookj and sorry about the issues you are having.

First of all, to have current flow, you need a "complete circuit". Just connecting thee batteries in series, with no load/charger/other current path--There should be no current flow.

Initially, it sounds like the batteries are wired "backwards"... Instead of +36 VDC to the golf cart, you have -36 VDC, and the current flow is (possibly) through the battery charger or something else (DC motor controller for golf cart, etc.).

You have to be very careful with DC Battery banks--They have a lot of current available (can be 100's or 1,000's of Amperes into a dead short) and the "attached" loads (battery charger, DC motor controller, etc.) can be ruined instantly too by the high reverse current/voltage.

If you have 3x 12 volt batteries sitting on the floor, and series connect the batteries together (+ to -, + to -). There should be ZERO current flow. Current flows in a closed loop of wiring.

You are welcome to post pictures here--And perhaps we can tell more from that.

Also--It is rare--But it is possible for batteries to have + and - terminals reversed (improper manufacturing, custom requirements, etc.)... Always use your volt meter to check the battery + and - terminals are correct (you read +12 volts, not -12 volts). That is the only way that everything could be correct with the golf cart install, but things still went wrong--But that is going to be a very rare event--I would doubt that this happened here--But somehow, + and - connections are not correct). Batteries with posts should have two post diameters so you cannot mix + and - connections to the batteries (if I recall correctly, the positive post is larger diameter than the negative post). Flag/bolted up connections--No obvious polarity "control".

Using Red and Black tape to mark cables back to the cart would be a good idea--It the cables are not marked now. Black/unmarked cables bundled together can get confused very easily.

-Bill

cookj

Thank you I will get some pictures and I’ll also test the batteries to make sure the terminals are not mixed up. 

I had them connected in series (-to+) should I start with +to- I’m not sure if that will make difference but I could try it. 

BB.

If there are no other connections, connecting the battery to battery "series straps", does not matter the order connected (- to +, or + to -).

You can check the first - and last + terminals (not yet connected) and make sure they show around 36 VDC, and you know the + and - polarity are correct (again, as I recall, the + terminal of round post batteries is larger in diameter than the - post of these batteries--If all is correct).

When you go to connect the 36 volt "bank" of batteries to the cart, then there is a "correct" order to connect the cart cables.

Assuming the cart is Negative ground (somewhere, the negative cart lead is bolted to metal frame/chassis somewhere--The idea is to connect the positive cart cable first (negative still not connected). Using metal wrenches on the + cable end will not spark if they hit cart sheet metal because the negative lead is still not connected (no possible current flow). After the + cable is bolted up, now connect the negative cable to the battery post. And if you hit a wrench to the cart sheet metal, there should be no sparks as the negative cable is already "grounded" to the cart chassis.

This is the reason there is an "order" to electrical connections.

 Some other hints:

Wear glasses / face shield to protect against acid spray/sparks... Lead Acid batteries generate hydrogen+oxygen gasses while charging. And it is pretty easy for a spark to ignite the H+O in the cells and cause a small explosion (spray battery plastic and electrolyte/acid around).

I like to put an old towel on top of a battery to protect it if I think there could be sparks (and keep any acid off of my clothes/sleeves).

Another precaution is to take your wrenches and wrap electrical tape around the handles and shanks of the tools to protect against accidental shorts. Wrapping tools usually done by electricians that have to work on "live circuits". And the most paraniod, will do new wrapping for every job to ensure that the handles are well protected.

If you do the + connection first, and the - connection second, the chances of your wrench causing a short is lessened. HOWEVER, you have three batteries with series connection straps/terminals--And you would not be the first person to drop a tool on a battery bank (and another reason I like to use a towel, plywood, etc. to protect the battery tops/connections).

Note that there can be "small" sparks (sometimes still fairly impressive) when making a final connection to the DC battery bus. For example, AC inverters can have good size filter capacitors on the DC input--And the spark is "charging" the filter caps. A quick touch the first time "charges the cap" and a second quick touch there should be no more sparks.

Being careful--Can help you live a long and healthy life.

-Bill