Yacht power audit

[mrangry]

I have a 44ft yacht which has four 110ah agm batteries as a house bank. To be honest, this figure was installed more by size limitations in the battery area than what I should have done by demand. I have no mains power or inverter just 12 volts dc. I do have a mains extension lead that allows me to plug into the marina on an ad-hoc basis if required. I have 300w solar which during the summer seemed to be fine, but noticed that my 440 ah house bank can fall to 60% on a winter overnighter with the fridge, lights and diesel heater in use.

I have also noticed that whilst the boat is unattended now during the winter that the house batteries can fall to 80% randomly, maybe once a week at around 3am. I am struggling to understand why this would happen as the only item left on is an auto bilge pump and the bilge is always dry.

I also want to carry out as accurately as possible a power audit of my requirements which I should have done before rewiring the boat to be honest. Does anyone have any suggestions on the best way to carry this out? Is it simply a painstaking case of using a clamp meter on each circuit individually to check draw? Has anyone done this or have any suggestions.

 

[KompetentKrew]

I'm sorry I may be unable to help, but how do you know that the batteries fall to 80% randomly?

What are you using to measure %age?

Generally this seems pretty acceptable to me - 60% or 80% occasionally is not going to kill your batteries, and it seems like you have enough solar for the times when you're actually using the boat.

I would arrange to have a charger on all the time when on shore power - a multistage charger gives only a maintenance trickle once the batteries are full, and you use as much power as you like when overnighting at the marina.

 

[QBhoy]

Cold temperatures or quickly changing temperatures, have a serious effect on batteries, it’s worth knowing. Hope that helps.

 

[mrangry]

Sorry i should have said, the charge state is measured by a Ctek D250 se and smartpass units via a phone app.

 

[dunedin]

……… I have 300w solar which during the summer seemed to be fine, but noticed that my 440 ah house bank can fall to 60% on a winter overnighter with the fridge, lights and diesel heater in use.……

Yes you need to do a power consumption audit - as I would expect that running a diesel heater on a long winter evening would indeed consume quite a bit of power, and with a warm cabin the fridge consumption will go up also.
So a substantial power drop if not on shore power seems quite normal to me. But worth looking up the specs and doingthe maths.

Also, have you fitted 100% LED cabin light bulbs? This is the first no brainer change for use off grid (except if only using the boat in northern waters mid summer)

 

[mrangry]

Yes you need to do a power consumption audit - as I would expect that running a diesel heater on a long winter evening would indeed consume quite a bit of power, and with a warm cabin the fridge consumption will go up also.
So a substantial power drop if not on shore power seems quite normal to me. But worth looking up the specs and doingthe maths.

Also, have you fitted 100% LED cabin light bulbs? This is the first no brainer change for use off grid (except if only using the boat in northern waters mid summer)

I have replaced all of the cabin lights with LED bulbs but as you say, the fridge and heater are pretty power hungry.
I have an automotive trickle charger that I plug into the mains extension lead when in a marina but just wonder do I need a bigger house bank for when on the hook for a few nights. I suppose a power audit will answer this but certainly seems like this may be the case.....where to put even more batteries

 

[Tranona]

Suspect your biggest problem is that your batteries are never fully charged relying on just the alternator and solar while having periods of heavy discharge. If you have access to shorepower the use it by fitting a proper 40A marine charger. The discharge is worrying but your monitor should show if there is any current draw when switched off. My AGMS have minimal self discharge and I only put the charger on if the resting voltage in the winter falls below 12.7 - usually no more than twice between November and April. Also if I have had a heavy usage weekend and little motoring I out in the charger for a day on return to bring the batteries up to full.

 

[BabaYaga]

I have also noticed that whilst the boat is unattended now during the winter that the house batteries can fall to 80% randomly, maybe once a week at around 3am. I am struggling to understand why this would happen as the only item left on is an auto bilge pump and the bilge is always dry.

Sorry i should have said, the charge state is measured by a Ctek D250 se and smartpass units via a phone app.

Are you using CTEKs XTC Battery sense monitor and phone app? I seem to remember that the first version of this system, +5 yrs ago, only gave battery charge status as a percentage. Also seem to recall reading some unfavorable user reports.
My understanding is that the current version gives a voltage figure. Perhaps it is more reliable over all.

 

[mrangry]

Are you using CTEKs XTC Battery sense monitor and phone app? I seem to remember that the first version of this system, +5 yrs ago, only gave battery charge status as a percentage. Also seem to recall reading some unfavorable user reports.
My understanding is that the current version gives a voltage figure. Perhaps it is more reliable over all.

I am indeed using the battery sense monitor and phone app. It gives me a percentage, temperature and voltage reading of one of the four batteries which are all connected in parallel.

 

[mrangry]

Suspect your biggest problem is that your batteries are never fully charged relying on just the alternator and solar while having periods of heavy discharge. If you have access to shorepower the use it by fitting a proper 40A marine charger. The discharge is worrying but your monitor should show if there is any current draw when switched off. My AGMS have minimal self discharge and I only put the charger on if the resting voltage in the winter falls below 12.7 - usually no more than twice between November and April. Also if I have had a heavy usage weekend and little motoring I out in the charger for a day on return to bring the batteries up to full.

Just when you thought you cant spend any more money.....I am now looking at multi-stage 40amp chargers online...what to chose.

 

[LadyInBed]

How old are the batteries?
Have you done any checks to see if any are under performing?

 

[mrangry]

How old are the batteries?
Have you done any checks to see if any are under performing?

I bought them boxed as part of a job lot from a guy who was going to fit out a camper van. I cannot see any dates on them but they were boxed and sealed, although dont know for how long. I have not as yet performed any checks on them as yet but keen to hear any suggestions on the best way of testing them.

 

[KompetentKrew]

do I need a bigger house bank for when on the hook for a few nights.

I haves a smaller bank of batteries (330Ah total) and probably less solar than you, and can manage on the hook for about a week. However that is pushing it - I am switching the fridge off by the 3rd day and the battery voltage gets much lower than I'd like by the end of the week. A day or two is fine.

 

[roaringgirl]

Yes, if you want to do a power audit, you'll either need to fit a shunt and run one thing at a time, or use a clamp meter. I recommend fitting a shunt anyway as it gives you a much better picture of what's going on. Are you aiming for self-sufficiency, or just a few days away from the marina. If self-sufficiency, then you might need to look at more off-grid charging capability; if just more days between marinas, then maybe a little more capacity.

To put it in perspective, my family of 4 lives aboard full time. We have 540Ah of AGM, 730W of PV, a wind-generator and a towed-generator. When everything is working as it should*, we make enough power that we can run our watermaker to keep our tanks full without ever having to burn diesel.

*waiting for new batteries as the current ones are on the way out.