Out of depth electrics

[sailorboy1944]

Currently on a mooring, have 3 x 100amp house battery's. 2x80w panels & Rutland going through a Marlec charge regular. Both are charging Btys. Have Merlin smart gauge which shows 80% charge at night. I switch of Btys with nothing running at night. In morning it shows 15%
Is there a simple answer. The Btys are just over a year old.

 

[prv]

That has to be the Smartgauge misreading - if there was that much energy really coming out of the batteries in a few hours you'd know about it.

You mention turning the batteries off - I don't suppose someone has wired the Smartgauge after the switch, have they? The Smartgauge needs to be wired direct to the battery and left on at all times - it will lose sync if it is disconnected.

Pete

 

[sailorboy1944]

I turned the batteries off to try & find the cause, smartgauge on all the time. Could it be the batteries not holding their charge?

 

[temptress]

I turned the batteries off to try & find the cause, smartgauge on all the time. Could it be the batteries not holding their charge?

Do you have a digital multi-meter on-board? What is the voltage at the batteries at each of the stages above? also what type of batteries do you have? Rough guide 11.9v battery discharged - 12.8 battery full (may read up to 14v (13.1-6 more usual) if solar is putting in charge....)

It could be lots of things. i would first determine if the batteries are charged, then look at the monitor. These usually work by counting AMP hours and are more likely to show you with charge left when the battery fails that the symptoms you are experiencing. It is likely an issue with the meter or the wiring of something. I would start with the batteries and work from there.

 

[prv]

These usually work by counting AMP hours

The Smartgauge is different to most others, and doesn't work by counting amp (or AMP) hours. Instead it tracks the exact terminal voltage of the battery and how it varies over time, and matches that to a stored model of battery charge and discharge to decide where in the process it is. The details are a trade secret, which always makes me a little dubious, but I have read lots of reports from sensible people saying that it works.

(The technique of tracking voltages over time explains why it must never be disconnected from the battery it is monitoring.)

Pete

 

[halcyon]

Currently on a mooring, have 3 x 100amp house battery's. 2x80w panels & Rutland going through a Marlec charge regular. Both are charging Btys. Have Merlin smart gauge which shows 80% charge at night. I switch of Btys with nothing running at night. In morning it shows 15%
Is there a simple answer. The Btys are just over a year old.

Have you got a multimeter on board ? if so in the evening last thing check the battery voltage at the terminals with little power being drawn, in the morning check them again. If the voltage is about the same the gauge is miss reading, if the voltage has gone down 0.5 volt you have a problem.

One problem is you have new batteries, the charged voltage of these will increase each time you charge them, you may well see 13 + volts no load, then as the battery gets old this voltage falls in time to 12.7 / 12.8 volt. The problem then is relating voltage to capacity, plus battery voltage for a given capacity varies with load, it's like measuring elastic.

Brian

 

[prv]

Have you got a multimeter on board ? if so in the evening last thing check the battery voltage at the terminals with little power being drawn, in the morning check them again. If the voltage is about the same the gauge is miss reading, if the voltage has gone down 0.5 volt you have a problem.

+1 - an excellent first step. Determine whether the problem is the gauge or the batteries.

(Despite being a fan of the product, my money is on the gauge, or more likely the way it's installed. I just can't see where nearly 200 amp-hours is going without anybody noticing. Say the OP sleeps for eight hours, that's a continuous drain of 30+ amps, something ought to be bursting into flames. Or possibly the battery is comprehensively knackered so there's nothing like 300AH to play with, but you'd hope not at one year old.)

Pete

 

[halcyon]

(Despite being a fan of the product, my money is on the gauge, or more likely the way it's installed. I just can't see where nearly 200 amp-hours is going without anybody noticing. Say the OP sleeps for eight hours, that's a continuous drain of 30+ amps, something ought to be bursting into flames. Or possibly the battery is comprehensively knackered so there's nothing like 300AH to play with, but you'd hope not at one year old.)

Pete

I have a theory on how the gauge works now, just need to find one on Ebay to confirm if follows my capacities, just don't like not knowing how things work.

The one possible reason for the loss of 200 amp-hours is surface charge, in the evening you have a high voltage due to surface charge and the gauge reads an appropriate capacity. The voltage is then slowly falling through the night as the battery settles and any small loads drain a little capacity. The gauge then tracks this falling voltage, assuming it is a discharging battery voltage and reduces the capacity, hence the reading we see in the morning.

Brian

 

[prv]

If it does turn out to be the gauge (ie, battery still reads a healthy terminal voltage on the multimeter) then I'd suggest contacting david.small@merlinequipment.com for advice. Ideally you'd contact "Gibbo", the bloke who designed it, but he has retired from selling the things and passed it all over to Merlin. Having spoken to them at the Boat Show a few years ago, they are knowledgable about the device and how it works, not just box shifters.

One other thought occurs - do you have it set to the right battery type? As in flooded, AGM, etc. This alters which model it uses to track the charge and discharge cycle.

Pete