First attempt at Power Audit - missed anything?

[robtheplod]

Hi All

 

I've done my first power audit to get an idea of what I could in theory be using. Gone a bit OTT with some things I know but just wanted to check I'm on the right path - any glaring errors or omissions? This is all in prep for solar next year after I've painted my roof..... based on this what would be the recommended amount of solar to pump this loss back into the batteries in a day?

 

[Alan de Enfield]

You cannot mix 230v and 12v in the same table.

 

The 230 volt appliances will be running using an inverter, to estimate the 'amps' at 12 volts you need to divide the watts by 10.

So, for example your washing machine is 1550 watts ao that equates to 155 amps from the batteries, running for 2 hours means 310Ah.

 

BUT

 

Your washing machine will not be using that much for the whole 2 hours, some time will be with the heater, some just spinning, etc etc so your calculation cannot be 2x max current.

For a couple of £'s you can but a plug in 'watt' meter, plug it in, plug your washing machine into it and run a full cycle and it will tell you how many Wh it uses. Divide this by 10 and you will have the Ah taken from the batteries.

 

Do the same with the lap-top - your laptop will be using something like 4.5 amps so 5 hours will be 22Ah

 

Edit to add picture of 'watt counter' (about £12 on Amazon, less on Ebay)

 

Edited October 25, 2020 by Alan de Enfield

[Tony Brooks]

As well as what Alan says you seem to think the batteries will retain their rated capacity for the long term. Lead acids will not so a rough rule of thumb is install four times the result of the power audit. Of more importance perhaps is what will be the charging regime when there is virtual no solar output.

 

As far as the amount of solar you need to recharge in a day then you tell us the amount of bright sunlight that will be available on each day. Of course you can't so the answer is as much as you can afford or fit on the boat. The more you fit the fewer winter weeks you will have insufficient to cover your discharge but it is very likely you will still need land line, engine, or generator charging during the winter.

[robtheplod]

That monitor looks useful Alan, thanks, all ordered. I shall test these devices and see what they actually show.

 

Tony, thanks for your reply. I have currently 4 x 110ah batteries so might just scrape through depending on results of further testing. Point taken re solar - more the better.. had suspected as such plus they would have the added benefit of cooling the roof? 

[ditchcrawler]

I think your USB charging could be well OTT unless you are constantly charging loads of things, 2 shower pumps?  

[robtheplod]

1 minute ago, ditchcrawler said:

I think your USB charging could be well OTT unless you are constantly charging loads of things, 2 shower pumps?  

well spotted re shower pump, that'll help!!

i have two sons who visit with their gadgets so being cautious!

[noone]

I live aboard and have approx 350-400w (fitted years ago,I've forgotten the actually outputs!? )of solar,charging 3x110 Ah lead acids.I use a 12v fridge/tv/C.B & H.F. radios/a stereo,with 12v amp/2 water pumps (not including the 2 bilge pumps I have,as they rarely get used)/all lights are 12v L.E.D.

On the 240v side,I have a twin tub and laptop (19v,so needs 240v to charge).In the summer,I have electricity to share!,and do so,(charging 240v items for friends),Winter sees me charging with my engine (120 amp alternator that charges leisure batteries only),every evening,after sunset,for around 15-30 mins.Sometimes of a morning for about the same time,if it is overcast.

Hope this is helpful  ?

[Alan de Enfield]

12 minutes ago, Leggers do it lying down said:

................... laptop (19v,so needs 240v to charge)

You can save a 'lot of leccy' by using 12v to charge it.

 

My laptop is 19v and I have a 12v to 19v adapter that plugd onto the cigarette lighter sockets.

Comes with a host of 'adapters' to suit all (?) laptops.

 

Seems daft to take 12v DC take it up to 230v AC then back down to 19v DC with all the losses at each stage.

If you don;'t need to have the inverter on just use the adapter and gp 12v Dc directly to 19v DC

 

[noone]

7 minutes ago, Alan de Enfield said:

You can save a 'lot of leccy' by using 12v to charge it.

 

My laptop is 19v and I have a 12v to 19v adapter that plugd onto the cigarette lighter sockets.

Comes with a host of 'adapters' to suit all (?) laptops.

 

Seems daft to take 12v DC take it up to 230v AC then back down to 19v DC with all the losses at each stage.

If you don;'t need to have the inverter on just use the adapter and gp 12v Dc directly to 19v DC

 

I have tried 3 different types of these,they all went up in smoke!??

[Alan de Enfield]

3 minutes ago, Leggers do it lying down said:

I have tried 3 different types of these,they all went up in smoke!??

 

They are available in different 'sizes' maybe the ones you bought were low-wattage.

You do have to be careful which one you buy.

 

I made sure that the one I bought was equivalent / greater than the rating on the mains adapter (output 3.4 amps)).

Edited October 25, 2020 by Alan de Enfield

[system 4-50]

34 minutes ago, Leggers do it lying down said:

Winter sees me charging with my engine (120 amp alternator that charges leisure batteries only),every evening,after sunset,for around 15-30 mins.Sometimes of a morning for about the same time,if it is overcast.

That doesn't sound long enough, imho.  Are you monitoring the charge current?

[noone]

The last time I tried one was about 5 years ago,all singing,all dancing item from Maplins.Quite a substantial looking thing,but the magic smoke escaped and it stopped working!

Maybe the tec has gotten better,I will maybe try again.As you say,stepping up to 240 then down to 19 is very wasteful.

[noone]

3 minutes ago, system 4-50 said:

That doesn't sound long enough, imho.  Are you monitoring the charge current?

Has kept me going for 15 years!..Charge is monitored,I usually switch off at about 10A.Deep winter can see me running for 30 mins morning & evening (with inverter on,charging the 240v I will use for the day,also,I only use the twin tub when engine is running!).

(The pic shows what my solar is currently putting in)

[Dr Bob]

4 hours ago, robtheplod said:

Hi All

 

I've done my first power audit to get an idea of what I could in theory be using. Gone a bit OTT with some things I know but just wanted to check I'm on the right path - any glaring errors or omissions? This is all in prep for solar next year after I've painted my roof..... based on this what would be the recommended amount of solar to pump this loss back into the batteries in a day?

 

I've never done a power audit on our boats - but the old one used to be around 120Ahrs per day and the new one 160Ahrs per day. Your usages seem pretty much what we did on our old boat. The washing machine was only ever run on 'cold' and when the engine was running so delete the washing machine entry - and the other 240V numbers! TV's, routers, Pi's do take quite a bit of power so your 120Ahr looks as good as you will get.

As others said, how are you going to get that back in with no solar. Likely 3 hours engine running per day. You need at least 4 times the 120Ahrs to survive not running the engine one day. I would go for 6*110Ahrs.

For solar, its not so much about how much you need to replace power as the sun does not always shine. When its hot, do you park under trees? The sun doesnt shine under trees. Directionally I would go for 250W of panels - a couple of panels - for top up, but if you are after maximum charging then 500W worked well for us but you wont get 120Ahrs out of 500W every day - far less. 500W is likely to be 4 panels on the roof which is a bit of an eyesore. 500W is likely to give 30A max charge as long as the sun is shining.

Our old boat had 500W in 4 panels but we have not fitted solar to the new one as I have Li batteries and a 240A alternator. I dont like the look of panels and they get in the way when doing locks.

[tehmarks]

One glaring error - as Alan alludes to, you haven't converted back to '12V land' with your 230V appliances, so the A/h figure you get for them is meaningless in the context you're using it in. You're looking at current at 230V, whereas you need to know current at 12V. Divide the power by 12 instead of 230, and add a small fudge factor for invertor inefficiencies (Victron invertors consume approximately 18W without actually doing anything, to give you a ballpark figure).

 

Edit

Bimble have a useful solar calculator which will give you a reasonable starting point. I'd be doubling (again) your battery capacity though, at least. The sun is fickle, and so the ability to go a couple of days without charge to 'fill in' the variability of solar charging is really quite important. If you go for the bare minimum you need for your average daily consumption, you'll be running the engine every single cloudy day you're aboard.

Edited October 25, 2020 by tehmarks

[LadyG]

I have 2 x 275 watt solar panels, in front of the sliding hatch, looks OK, keeps nominal 600 ah batteries topped up, gives me autonomy for up to five overcast days, but I have very limited demand.

 

Edited October 25, 2020 by LadyG

[David Mack]

34W sounds low for a fridge.

[Alan de Enfield]

32 minutes ago, David Mack said:

34W sounds low for a fridge.

 

My Waeco CR80 quotes "average power consumption = 40w"

 

I have measured the actual usage and it comes out at ~30Ah per day, so RobthepLod's extrapolation of 34Ah per day may not be far out.

 

 

Edited October 25, 2020 by Alan de Enfield

[robtheplod]

8 hours ago, David Mack said:

34W sounds low for a fridge.

I'll double check the wattage when next on the boat - its a 12v shoreline - I've guessed its on 12hrs in 24hrs....

[DandV]

7 hours ago, Alan de Enfield said:

 

My Waeco CR80 quotes "average power consumption = 40w"

 

I have measured the actual usage and it comes out at ~30Ah per day, so RobthepLod's extrapolation of 34Ah per day may not be far out.

 

 

Our 12v shoreline, danfoss compressor was about averaged40w  during the six month UK summer season so would have been less if averaged over the whole year. It was by far the biggest load on a boat whith all led lighting, The Inverter was only run when the engine was running and the washing machine was running on cold cycle. 

[Tony Brooks]

19 minutes ago, robtheplod said:

I'll double check the wattage when next on the boat - its a 12v shoreline - I've guessed its on 12hrs in 24hrs....

Watch out for any wattage stated by Shoreline The case may still have its 240V label on it.

 

The 12V consumption figures may be the average over 24 hours and not the instantaneous figure. If so you can't use a 12 hour run time.

[Alan de Enfield]

1 hour ago, robtheplod said:

I'll double check the wattage when next on the boat - its a 12v shoreline - I've guessed its on 12hrs in 24hrs....

Depending on 'circumstances' mine is on about 1/3rd of the time (about 20 minutes per hour)

During the night it 'clicks on / off' about midnight, 4am and then 8am

 

During the day, opening the door for milk for the numerous mugs of tea, lunch, dinner etc means it runs more frequently.

The ambient temperature also has a big part to play, as does the amount of ventilation around the installation.

[robtheplod]

2 minutes ago, Alan de Enfield said:

Depending on 'circumstances' mine is on about 1/3rd of the time (about 20 minutes per hour)

During the night it 'clicks on / off' about midnight, 4am and then 8am

 

During the day, opening the door for milk for the numerous mugs of tea, lunch, dinner etc means it runs more frequently.

The ambient temperature also has a big part to play, as does the amount of ventilation around the installation.

as an aside to all this, I've heard that having a hole/gap under the fridge into the bilge is beneficial for ventilation - presume it pulls in cooler air?  does this stack up or is it a tale?

[Keeping Up]

4 minutes ago, robtheplod said:

as an aside to all this, I've heard that having a hole/gap under the fridge into the bilge is beneficial for ventilation - presume it pulls in cooler air?  does this stack up or is it a tale?

On it's own the hole would not do much, but with a small computer fan in the hole it is very effective.

[Tony Brooks]

I cut holes in mine and some fit fans over the holes controlled by the fridge itself. As long as the warmed air has an exit it should help.