Low voltage issue

[mattonthesea]

I have three, 80amphour, leisure batteries often charged by shore power. Off grid we have 130 watt PV. Until recently this has been enough to keep our Standard Horizon VHF, Raspberry pi III plus 10" monitor, tiller pilot and Clipper Duet happily running, even in poor sunlight, all day.

However, recently, after two or three hours, the VHF has given a low voltage warning, and turned off when I attempted transmission. The battery monitor said 12.5 volts so not that low? It had read 12.8 when we set off.

The only change I can think of is that when I rewired the fridge (not used during passage) I wired it directly to the negative terminal rather than through the BM. Could this be a problem?

One of the batteries came with the boat so over 6 years old. The other two are two and three years old. Could the old one be reducing the effectiveness of the newer ones?

Puzzled

M

 

[Pye_End]

Are they open? Ie can you use a hydrometer? Worth taking the old one out the system and seeing if it improves.

Sounds like battery - 12.5v after not too long from fully charged with not a lot taken out.

Double check voltages with a multimeter - just in case it is a connection problem.

 

[VicS]

Maybe a bad connection in the supply to the VHF. Could be in the positive or the negative. In line fuse ????
Check the volts as close as possible to the VHF while attempting to transmit.
As Pye End suggests take the old battery out of service and see if that helps

If your fridge is connected directly to the battery negative the monitor will not see the current it is taking. All connections should be to the shunt. but this is not causing the problem with the VHF

 

[ltcom]

12.5 V is half charged IIRC. On a sunny day starting out i would expect to see 13 V or more.

 

[KompetentKrew]

The only change I can think of is that when I rewired the fridge (not used during passage) I wired it directly to the negative terminal rather than through the BM. Could this be a problem?

I assume that by "BM", you mean battery monitor.

This is technically fine if you never use the fridge at any time you're not on shore power, but the next owner of your boat is going to be so annoyed at you when he inevitably wrecks the boat's batteries, because he's not going to be expecting that.

The whole point of a battery monitor is that everything goes through it, so you can measure how much battery you've used.

If a careless member of crew leaves the fridge on for some time, before you notice, then you won't know how much has been used.

If you're using the fridge at anchor then it may be that it's you who has run the batteries too low, because your BM was not able to monitor how much leccy has been going in and out of them. Otherwise, my spidey-sense says dodgy connection in the supply to the VHF - check spade connectors and fuse holders for corrosion.

 

[mattonthesea]

I assume that by "BM", you mean battery monitor.

This is technically fine if you never use the fridge at any time you're not on shore power, but the next owner of your boat is going to be so annoyed at you when he inevitably wrecks the boat's batteries, because he's not going to be expecting that.

The whole point of a battery monitor is that everything goes through it, so you can measure how much battery you've used.

If a careless member of crew leaves the fridge on for some time, before you notice, then you won't know how much has been used.

If you're using the fridge at anchor then it may be that it's you who has run the batteries too low, because your BM was not able to monitor how much leccy has been going in and out of them. Otherwise, my spidey-sense says dodgy connection in the supply to the VHF - check spade connectors and fuse holders for corrosion.

Next job on the list is to sort the tangle of wiring around the battery box ? This is a temporary fix - but don't they all say that! The only reason I didn't do it properly was that it was below zero when I rewired the fridge and too cold to work out how the BM was wired.

Plan is to replace domestic wires with tinned and bus bars.

I suspect that the VHF wires are also poor quality so I'll do that at the same time.

PS we're approaching the end of season in Sweden as our 90 days are running out. Means that I won't have time this season so I'll give an update next year. Thanks for everyone's help

M