More battery talk

[PaulRainbow]

That's all fine in theory, but for our purposes what do we really want to know?
If you are trying to make decisions based on whether our battery is 80% or 70% charged, then you need some way of repeatably indicating this.
It does not have to be accurate, just repeatable.
E.g. if the real question is 'can I run my fridge overnight without plugging in?', then you need an indication good enough to tell you that.
A voltage and a bit of knowledge of what the battery has been doing for the previous day, together with a bit of history of monitoring voltage with typical loads, will enable the decision.

A battery charger is trying to evaluate the state of charge in terms of the question 'is it beneficial to keep charging?'

The % charge under some arbitrary lab conditions is all very interesting, but the lab conditions are out of the window on a boat.

A lot of good sense there IMO. I'm not really interested in lab tests, theories or quoted snippets from manufacturers. I am interested in what's happening on my boat, in the real World.

 

[PaulRainbow]

Wouldnt a good indication of how well you are charging the batteries be the voltage in the morning? Over night there will just be the fridge running and a few LED lights for most people so before the sun comes up the resting voltage less a bit for the fridge would give you a pretty good idea of where you are at.

I think so, which is why i posted the short rested figure from yesterday evening and this mornings figure. This mornings figure was 12.4v, that's after an evening with the Eber on and a few LED lights, plus the fridge. So i'm happy that the batteries must have been at least reasonably well charged.

I haven't had the mains charger on for 2 months and the engine has had very little use. That also suggests to me the solar panels are doing a good job.

 

[RobbieW]

The battery monitor isn't helpful with daily ah figures, it gives lowest and total, but no average and doesn't say how many days the total is for. But, it looks to be something like 25ah. During the night the only thing that is on is the fridge. At the moment the Eber comes on for a couple of hours around the time the alarm goes off, it's also on in the evening for a short time. Lights are all LED, water is electrically pumped, FM radio on most of the time i'm onboard. The laptop is currently charged via mains, as the previous solar panels couldn't keep up, but this will be changed to 12v in the next few days.

Thanks Paul, knowing your electrical 'budget' is, imo, essential to building a good charging system. Whilst your existing system copes easily with the loads you have now, as you extend those loads the ability of solar to cope will diminish. My cruising 'budget' is around 100a/day, on a good day solar puts in c. 60a which means I want to top that up from another source every 3-4 days.

 

[PaulRainbow]

Thanks Paul, knowing your electrical 'budget' is, imo, essential to building a good charging system. Whilst your existing system copes easily with the loads you have now, as you extend those loads the ability of solar to cope will diminish. My cruising 'budget' is around 100a/day, on a good day solar puts in c. 60a which means I want to top that up from another source every 3-4 days.

I only had 120w of solar and 2x110ah batteries last year, so didn't run the laptop from the batteries when in the marina. I've now added another battery and increased the solar panels to 260w, so i expect to be able to comfortably run the laptop from the 12v systems now. I think i should be self sufficient during the Summer, but expect to have to supplement the solar during Winter.