Measuring Amps - for Liveaboards :)

[Higgs]

well then.....interestingly......it might not take THAT many solar panels to achieve the same 30Amps (for 3hrs). That would save 3hrs diesel and 100hrs a month saved in engine running. Solar is looking attractive if the 175 alternator is only actually a 30 alternator.

 

100W solar = 5amps.

600W solar = 30amps.

 

Right?

 

Lab conditions, optimum. Variable, day to day and seasonal. Cloudy, high sun, low sun. Directional.

[nb Innisfree]

10 or 12A is quite a high terminating current for bats in good condition - our 440AH bank of cheapo leisures gets down to below 1A at 14.6v after a long day's cruise. I would go lower on the once a week charge, especially if you can be doing something else useful with the engine (you could try cruising!)

We once saw a charge rate of about 0.1% of batt capacity! That was based on there being just under 50% of capacity left in or bank of eight 120 ah batts, a bit of a guess maybe but we did see 0.2 amps charge rate on our BMV monitor (24v) after three days charging.

[DeanS]

Yep. Running the engine for 1hr in the mornings, and then relying on solar for the rest of the day would seem the way to go. I'll need to do some calculations to see how much fuel I might save, which I can channel into buying panels. If possible over a year, then it would mean next year, I'll have a lower fuel bill, and the panels will be paid off. It's not all about an immediate solution...I'm very much also thinking about the years to come. In the past I thought that running the boat engine far exceeded what solar could produce, but todays measurements have been astounding....if the boat is dropping to 30Amps on the clampmeter relatively quickly (I will test tomorrow morning how fast it drops to 30) then solar can achieve that. At the same time, I might just look at getting more batteries instead of solar.....so like I said...lots to think about...but having this little clamp meter is wonderful.

 

ps...if I just stick amphour in front of all my values, will I be more correct? eg..the battery capacity is x amphour. The alternator was supplying 30amphour. The supply to the invertor was x amphour. It seems the more I just say amps, the more I am corrected.

 

 

ETA - I have used about £150 of diesel in the past month. Mostly for charging batts. The boat has done about 100hours. If I ran it (for charging) 1hr per day, I'd save 60hrs running per month...which is about £80 diesel. If I put that saving towards solar, I could pay back my solar investment by year end.

Edited April 23, 2013 by DeanS

[Higgs]

I'm very much also thinking about the years to come. In the past I thought that running the boat engine far exceeded what solar could produce, but todays measurements have been astounding....

 

The thought of using renewables is appealing, and may not give instant financial return, but unless charging whilst cruising, I've always thought it poor use of the engine just to be used as a battery charger. So, wind and solar equipment saves some of the wear on the engine.

[nb Innisfree]

ps...if I just stick amphour in front of all my values, will I be more correct? eg..the battery capacity is x amphour. The alternator was supplying 30amphour. The supply to the invertor was x amphour. It seems the more I just say amps, the more I am corrected.

 

Nope, wrong again. An alternator produces power measured in amps. If it produces a steady 30 amps for one hour that will equal 30 amphours. If it produces a steady 30 amps for one and a half hours it will equal 45 amphours. (30 x1.5 = 45)

 

Just giving something a name won't make it right!

[DeanS]

Nope, wrong again. An alternator produces power measured in amps. If it produces a steady 30 amps for one hour that will equal 30 amphours. If it produces a steady 30 amps for one and a half hours it will equal 45 amphours. (30 x1.5 = 45)

 

Just giving something a name won't make it right!

 

Yes...I understand fully. I'll try and word my posts correctly then....I'll get it eventually. I understand that AH is capacity and flow of elec is Amps....and flow for an hour is......erm AH again?

[ditchcrawler]

Measured 10A on the meter.

Fridge on.

Laptop.

 

Those are on 24hrs. So thats 240Amps.

TV goes on for a few hours a day. 5Amps x 6 = 30Amps.

This excludes water pumps, cell charging, IPad charger etc.

This excludes PS3...about 2hrs a day.

 

So most likely looking at over 200Amps per day usage.

 

This excludes washer and desktop, which run off gennie.

But your fridge should have a thermostat so unless you leave the door open its probably only running for 6 hrs in 24. and surly you go to sleep and don't use the laptop or do you run a shift system on the boat so the kids use it while you sleep.

[nb Innisfree]

 

Yes...I understand fully. I'll try and word my posts correctly then....I'll get it eventually. I understand that AH is capacity and flow of elec is Amps....and flow for an hour is......erm AH again?

Erm...yes.

 

We'll wait and see...

[Grace and Favour]

DeanS - - - you'll also discover that the solar panels are rather quieter than your engine

 

And don 't need as many changes of oil & oil/fuel filters either!

Edited April 23, 2013 by Grace & Favour

[Chris Pink]

 

Yes...I understand fully. I'll try and word my posts correctly then....I'll get it eventually. I understand that AH is capacity and flow of elec is Amps....and flow for an hour is......erm AH again?

Getting there.

 

Amp hours is how much you've got

Amps are how fast you are using it (or generating it)

 

I was thinking of explaining that amp hours are only a lazy way of describing kilowatt hours ( remember them? ) but the maths is more difficult. Hence we use amp hours as a shortcut.

[nb Innisfree]

'Knowing' is different to 'understanding'. You can learn a formula parrot fashion and know how to use it to calculate something. But you have to first picture it as an image, a sort of working model, to understand it.

[Arthur Brown]

Both charging sources have their place, both are needed. In the high summer solar cells will produce all your energy needs and charge the batteries gently, which is good for their long life. in the dead of winter the solar panels needed to supply your energy needs would sink the boat so the generator is needed.

 

Each day, early in the morning, decide whether a charge is needed. Put some charge in by generator first thing, then leave the solar to put in all the absorbtion and float charge sectors. With experience you will understand how long an engine run and how much solar is needed. A reasonable solar rig will satisfy your needs for about six months but need some generator assistance for the other months.

 

If you are planning not to run the engine for long then please consider a separate small solar panel for the starter battery, a flat house bank may not start the engine.

[David Mack]

When I started the engine 20mins ago, the alternator was pushing out 130 whatevers.

20min later it is pushing out 35 whatevers

 

WHAT'S THAT MEAN My understanding is that batteries tell the alternator how much they want. Why dont they want more? I very much doubt they are full.

Think of it like filling a lock. When you first open the top paddles on an empty lock it starts to fill quite fast. But as it gets towards full, the rate of filling slows down, and it can take ages to get the water level up those last few inches.

[nb Innisfree]

Or think of it as a water cistern, when the water level is low the valve is wide open and so flow (current in amps) is high but pressure (volts) is low. When it reaches the float ball it starts to reduce the flow and increase the pressure.

Edited April 23, 2013 by nb Innisfree

[DeanS]

Surly you go to sleep and don't use the laptop or do you run a shift system on the boat so the kids use it while you sleep.

 

 

exactly.

[DeanS]

'Knowing' is different to 'understanding'. You can learn a formula parrot fashion and know how to use it to calculate something. But you have to first picture it as an image, a sort of working model, to understand it.

 

Understanding I have. Batteries store power. Alternators supply power and recharge the batteries. If a battery can contain 330AmpHours worth, it means it can supply 1 Amp for 330hrs or 330Amps for 1hr. (right?) If an alternator is sending 30Amps ...for an entire hour..to the batteries....the batteries capacity would have increased by 30AH (right?) . The things I dont yet fully understand is how the amount of charging changes...based on the batteries condition. Now that I have my multiclamp thingamabob, I can take readings..which is very empowering, and the whole reason for this thread.

[nicknorman]

. If a battery can contain 330AmpHours worth, it means it can supply 1 Amp for 330hrs or 330Amps for 1hr. (right?)

Not that bit in the real world! Remember Peuket? He said that if you discharge rapidly you will get less out of the battery than if you discharge slowly. So if you get 1 amp for 330 hours to flat, you wont get 1 hour at 330A, the battery will be flat before that. And also of course, only ~1/2 the capacity is sensibly usable.

[nb Innisfree]

 

Understanding I have. Batteries store power. Alternators supply power and recharge the batteries. If a battery can contain 330AmpHours worth, it means it can supply 1 Amp for 330hrs or 330Amps for 1hr. (right?) If an alternator is sending 30Amps ...for an entire hour..to the batteries....the batteries capacity would have increased by 30AH (right?) . The things I dont yet fully understand is how the amount of charging changes...based on the batteries condition. Now that I have my multiclamp thingamabob, I can take readings..which is very empowering, and the whole reason for this thread.

First bit is correct in theory but in fact the heavier the load taken from the bat the lower the capacity it has, conversely the lighter the load taken the higher the capacity it has. Battery Ah capacity is normally stated as 20 hour rate, that is if a certain load is applied that will empty a batt from 100% state of charge down to 0% state of charge then that is the capacity at that load. So a 100ah batt at the 20 hr rating will equate to an average of a 5 amp load for 20 hrs, any more or less than 5amps will result in a different capacity.

[DeanS]

Thanks guys. It all helps.

[smileypete]

10 or 12A is quite a high terminating current for bats in good condition - our 440AH bank of cheapo leisures gets down to below 1A at 14.6v after a long day's cruise. I would go lower on the once a week charge, especially if you can be doing something else useful with the engine (you could try cruising!)

 

I'm just going by what The Battery FAQ says:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charged

 

Seems a reasonable rule of thumb for el-cheapo non sealed batts, although charging for longer is nice, I doubt it'll make a large difference to batt life.

 

cheers, Pete.

~smpt~

 

[nicknorman]

 

I'm just going by what The Battery FAQ says:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charged

 

Seems a reasonable rule of thumb for el-cheapo non sealed batts, although charging for longer is nice, I doubt it'll make a large difference to batt life.

 

cheers, Pete.

~smpt~

 

There is no "right answer" but I think with new bats its worth going lower, otherwise they never get fully charged and we all know what that means. As they age, the min current tends to increase so for mid life bats maybe that value is fine.

[Richard10002]

 

Understanding I have. Batteries store power. Alternators supply power and recharge the batteries. If a battery can contain 330AmpHours worth, it means it can supply 1 Amp for 330hrs or 330Amps for 1hr. (right?) If an alternator is sending 30Amps ...for an entire hour..to the batteries....the batteries capacity would have increased by 30AH (right?) . The things I dont yet fully understand is how the amount of charging changes...based on the batteries condition. Now that I have my multiclamp thingamabob, I can take readings..which is very empowering, and the whole reason for this thread.

At this stage of learning and understanding, you are close enough to being correct. Once you get a bit further in your understanding, it will become clear that it's not quite so simple.

 

On solar, I've got a 100W panel through a PWM controller and, so far, it doesn't come close to providing any worthwhile Ahs. It's fitted flat, as I didn't think I'd be motivated to move it about as the boat, or the sun, moves around. Angling it would improve things and maybe an MPPT controller may add a bit more, but I sense that you need a big solar bank to provide worthwhile liveaboard power.

[DeanS]

At this stage of learning and understanding, you are close enough to being correct. Once you get a bit further in your understanding, it will become clear that it's not quite so simple.

 

On solar, I've got a 100W panel through a PWM controller and, so far, it doesn't come close to providing any worthwhile Ahs. It's fitted flat, as I didn't think I'd be motivated to move it about as the boat, or the sun, moves around. Angling it would improve things and maybe an MPPT controller may add a bit more, but I sense that you need a big solar bank to provide worthwhile liveaboard power.

 

Yep..I've always looked at solar slightly cautiously. Our daily usage is approx 210Amps per day. Thats based on:

 

Fridge on by itself - 2Amps@8hrs = 16Amps

Fridge and laptop - 10Amps @16hrs = 160Amps

PS3 - 6Amps@4hrs = 24Amps

IPAD,TV,Laptop - 5Amps@2hrs = 10Amps

 

Total = 210Amps

 

This excludes lights, water pumps etc.

 

I'm supposed to put back 50% more than we use....so I should be putting back 300Amps into the batteries each day. If I cant, I have to cut down on appliances. Not likely. We've been in the boat for a month, and no evidence of the batteries struggling, so the charging regime seems to be working, except it's costing in diesel. ..and a bit of engine noise. (need to put soundproofing along the one side of the engine wall I think which would improve that). If I can generate half of that using solar, and the rest in a morning engine charge, that would be idylic.

 

ETA - thats the requirements for running a business from a boat, and keeping 3 kids happy in the evenings.

Edited April 23, 2013 by DeanS

[Paul C]

Yep..I've always looked at solar slightly cautiously. Our daily usage is approx 210Amps per day. Thats based on:

 

Fridge on by itself - 2Amps@8hrs = 16Amps

Fridge and laptop - 10Amps @16hrs = 160Amps

PS3 - 6Amps@4hrs = 24Amps

IPAD,TV,Laptop - 5Amps@2hrs = 10Amps

 

Total = 210Amps

 

Ummmm I'm confused, you've counted the fridge twice and you've counted "laptop" twice (2 different laptops?)

 

Also, the correct unit for the numbers on the right hand side and the total, is Amp hours.

 

If you've missed electrical items (lights, pumps etc) out then its not a total....its a subtotal. Make a guess of these, and you're 90% there to getting your power audit done.

[Scooby]

What if the sun doesnt come out. lol.

 

 

 

I have 2 x 100w solar panels with a mppt controller to each one, works great during the sunny days and we are power hungry too. We are getting around 10 amps per hour from both on a good sunny day. When the suns gone in its time for the engine lol. 3 years onboard, 4500 hours on the engine in the 3 years and solar for 2 and a half years. We did have some charging issues though which we have had sorted now, fuel per month is around £60-£80 a month now based on 94p per litre using about 1 and a half litres per hour, and some genny use but not much. hope this helps, i would recommend solar though, they worth it.

I hate the fridge so i fitted 2 computer fans underneath it to help stop it coming on all the time.