Batteries Batteries Batteries

[billyfish]

My almost new house Batteries are only showing 13.4 volts the starting Battery 14. They are 2 90 AH lead acid. Why won't they charge higher

 

[jamie N]

This from AI: "A fully charged 12V lead-acid battery typically rests at 12.6V to 12.8V or higher. When actively charging, the voltage rises to between 13.2V and 14.6V depending on temperature, while a 100% capacity "resting" voltage (after 24 hours without load) is approximately 12.85V."

For myself though, is that the max V that your charger's putting out, and is your DVM accurate?
Those volts would seem to be OKish.

 

[Tranona]

You don't say when the voltage readings are taken. 13.4 is a typical "float" charge for LA batteries. This means the battery is fully charged and the charger/alternator cuts the charge back. A fully charged battery will have a resting voltage of 12.7 to 12.8

 

[billyfish]

You don't say when the voltage readings are taken. 13.4 is a typical "float" charge for LA batteries. This means the battery is fully charged and the charger/alternator cuts the charge back. A fully charged battery will have a resting voltage of 12.7 to 12.8

OK they look OK. What i don't understand is the starter battery 80 AH reads 14 all the time.

 

[MontyMariner]

Parallel House batteries (you use the plural)?
If you connect one of them , measure that and the disconnected battery then swap them over and do the same again, what readings do you get?
One might be pulling the other down, but it's very marginal.
There might be a load on the house that isn't on the starter.

 

[ylop]

OK they look OK. What i don't understand is the starter battery 80 AH reads 14 all the time.

All the time? Or all the time with engine running (or mains charger on)? How are the batteries linked - 1-2-Both switch, a diode, a VSR, etc?

 

[billyfish]

All the time. With the engine running. Don't have mains power just a couple of solar panels from memory a 20 and 50 watt

 

[Mistroma]

You'd really need to give more information to be certain. Battery chemistry, wiring diagram, charging equipment and so on. However, 14V is about right for a start battery that's being charged by an alternator and NOT directly connected to the domestic batteries. Start batteries aren't cycled and should be virtually 100% state of charge and that means a basic alternator would show around 14-14.4V and that's what you have. Domestic batteries are cycled and often not at 100% charge they are usually isolated from the start battery and can have different charging methods. It's possible your domestic batteries aren't fully charged or they've been charging on shorepower or other system to 100% and are now on float. If they are at 100% that would mean they aren't directly charged from the alternator as they'd rise to 14V. You could have equipment designed to charge the batteries in a multi-step fashion using the alternator.

Lots of guesswork and assuming all batteries are lead acid. Do you know what charges the domestic batteries when the engine is running? Perhaps you have a DC-DC unit to charge the domestic batteries but start battery is simply charged from the alternator. The difference you see does point to some sort of "smart charging system" for the domestic batteries.

 

[billyfish]

I'm pretty hopeless with electric systems but get by. Which is why I've asked on here. I don't see any smart systems equipment to me it looks like the alternator charges the start battery then the house batteries. I leave solar on when not on board, seams to keep them up but no more than 13.4 v so I guess what you say is right and they are OK.

 

[Tranona]

I'm pretty hopeless with electric systems but get by. Which is why I've asked on here. I don't see any smart systems equipment to me it looks like the alternator charges the start battery then the house batteries. I leave solar on when not on board, seams to keep them up but no more than 13.4 v so I guess what you say is right and they are OK.

Difficult to make any sensible comment without knowing exactly how the charging is arranged - there are so many potential variations.

 

[billskip]

there are so many potential variations.

Or difference even.....

 

[fredrussell]

All the time. With the engine running.

This is a confusing description.

 

[billyfish]

I think it's working fine and the resting charge at 13.4 is fine. thanks all for helping . They will get me through the summer and refit time coming I'm planing to upgrade to one of the more modern alternatives

 

[ylop]

I think it's working fine and the resting charge at 13.4 is fine. thanks all for helping . They will get me through the summer and refit time coming I'm planing to upgrade to one of the more modern alternatives

"Resting charge" seems like a contradiction in terms. At rest a normal lead acid will be ~ 12.7V fully charged. If the "extra" is coming from the solar panels and each battery is fed from its own solar that might explain it - if the panels are different sizes or oriented differently, or if the engine battery is "full" and the house is actually being charged. It would be a misleading assumption that a battery reading 13.4 but connected to any charging source is actually full.

But its all guesswork unless you understand (and share) your wiring configuration. Its not difficult to trace the wires and draw a diagram. You may find boxes you don't understand but take a picture and post here along with the wiring. If you understand what you have, and what it is / isn't doing properly you'll be in a far better place to decide what any winter upgrade requires.

 

[Mistroma]

If I had to guess and there's not enough consistent information to give a decent diagnosis. I'd guess that IF the start battery is at 14.2V when the engine is running it is going to be well charged as you'd expect from a start battery. The domestic batteries could well be undercharged. That's very common and you said they don't go higher than 13.4V. Just continuing like that for a whole season isn't going to be optimal. However, they wouldn't be hugely undercharged and might be around 85%-90%.

I'm making lots of assumptions about likely battery types, usage pattern, wiring, etc. Could be bad connections or other reasons but 14.V start and 13.4V domestic make it a reasonable guess.