Hi. Im scratching my head here. I’ve got 2x12v 110Ah batteries connected in parallel connected to a Victron charger. Negative and power leads from battery 1 that connect to battery 2 read 14v unconnected. When connected to battery 2 voltage drops to 12.4v. Limited brain cells so easily confused

 

What does battery 2 read when not connected?

It sounds like battery 1 is charging battery 2.

When connecting batteries in parallel, they should start at the same voltage.

 

Best to charge batteries separately.

 

If the batteries are similar capacity, charging in parallel should be fine. They'll only accept the charge they need.

Looking at the wiring, though, it's a good idea to have a fuse or breaker as close to the positive terminal as possible. Apart from safety, it's convenient to be able to shut off everything at once.

 

A battery isolator would be the proper way to handle charging. Each battery takes the charge it needs. A switch on the output can isolate the batteries (chassis vs house in an RV for example) or bridge them together when needed.

 

If the batteries are similar capacity, charging in parallel should be fine. They'll only accept the charge they need.

Looking at the wiring, though, it's a good idea to have a fuse or breaker as close to the positive terminal as possible. Apart from safety, it's convenient to be able to shut off everything at once.

Thanks. I have 2 ready to fit.

 

Apparently not but thanks for the input

Best to charge batteries separately.

 

What does battery 2 read when not connected?

It sounds like battery 1 is charging battery 2.

When connecting batteries in parallel, they should start at the same voltage.

Despite checking the ohms with the cables showing zero the negative was full of verdigris. Renewed cable and now charging normally. Thanks for the input

 

First, the battery terminal voltage depends quite a bit on the state of charge. And the state of battery charge depends a fair amount on the connections to both the charger and the load. Consider that at ten amps, one milliohm resistance different results in ten millivolts difference.

 

While putting two batteries in parallel is a straight forward project, looking at the picture it's hard to tell exactly what goes where. Schematics is the language of electricity and electronics.

It's fairly easy to see the negative jumper between the two batteries but looking at the picture I see on the upper battery a whole lot more wiring going on; wires we know not where they go or what they do. As for seeing a battery at 14V, that's possible if the battery has just come off the charger. But if you're charging both batteries in parallel at the same time then both batteries should have an equal charge to them. If not then one battery is funky. 12.4V is what I'd expect to see on a used but healthy 12V battery when at rest (not being charged). 14V is what I'd expect to see when (on a car) the engine is running and the voltage can go as high as 15V shortly after starting the car. But quickly the voltage should drop (engine running) down to 13.6 to 13.8V.

What are the conditions you are testing at? Is there an engine running with an alternator? Have both batteries just come off a charger, charged independently? Were they charged while connected in parallel?

To see that kind of voltage (14V) something is up. A 12V battery shouldn't read that high at rest. What I mean by "at rest" is a battery that has not been charged for at least 12 hours and no load has been applied to it (aside from normal automotive memory maintenance and such things like a clock - etc.)

 

Now is the time to start measuring voltages between points that are supposed to be connected. Someplace there is a poor connection.

 

Another thread where the TS has lost interest. Or solved their problem and just neglected to inform us.

 

Another thread where the TS has lost interest. Or solved their problem and just neglected to inform us.

I guess you didn’t read post #8, where he discovered the problem and solved it.

 

I guess you didn’t read post #8

Guess I missed that.

 

I guess you didn’t read post #8, where he discovered the problem and solved it.

TS? Dodgy wannabe tech here.. Despite doing my best I regularly get a build up of verdigris on my connectors where I have to resolder connections after a year or so. I have no idea what I am doing wrong..

 

I am not familiar with the term " verdigris ", but if that is the same as corrosion buildup, it would be from using an acid type of solder flux, or possibly a wrong type of solder and too much heat. If it is on bolted connections, the trick is to first thoroughly clean the connection, then add some electrical connection anti-corrosion grease to cover it.

 

I am not familiar with the term " verdigris ", but if that is the same as corrosion buildup, it would be from using an acid type of solder flux, or possibly a wrong type of solder and too much heat. If it is on bolted connections, the trick is to first thoroughly clean the connection, then add some electrical connection anti-corrosion grease to cover it.

Yes a corrosion build up after time just below and into the soldered terminals. thanks for the tip, I'll give it a go when it happens again

 

Solder flux of the wrong kind will do exactly that: flow down between strands and cause corrosion later, as it absorbs moisture from the air. It is often fatal in the more delicate smaller electronics assemblies.

 

if I recall correctly I used flux I used when plumbing

 

hi,
Most plumbing fluxes are corrosive!
E