Need help with calculations

[J4mie82]

How long will my tv run for without damaging my battery?

I have a small boat and have been setting up the electrics. I have been given a 80w solar panel that is in good condition and a regulator. I would like to know how long I could run a tv on the set up I have.

Tv = 40 watts
Inverter = 400 watts
Battery = 88ah
Solar panel = 80w
Av hours of sun = 4

I have got so far...

Tv = 40 watts through a 400 watt inverter.

(Assuming that the inverter is 100% efficient)

40 watts/ 12 volts = 3.33 amps

88ah battery/ 3.33 amps = 26.4 hours of running time

13.2 hours if only discharging the battery by 50%

I have a solar panel that is 80w and gets approximately 4 hours of full sunlight.

(Assuming the solar panel puts out 100% efficiency for 4 hours)

80watts/12 volts = 6.66 amps

6.66 x 4 = 26.64 amps

How long will my tv continue to work without depleting the battery over 50%

[Sunking]

First thing to do is DO NOT WORK IN AMP HOURS, use watt hours, then convert to amp hours on the last step once battery voltage is selected.Secondly you have to factor in efficiency for either PWM (2) or MPPT (1.5) charging.OK lets say you want to run that TV for 4 hours per day, and you have a minimum 4 Sun Hour day, and the TV uses 40 watts. 40 watts x 4 hours = 160 watt hours. To find the battery capacity needed you want a minimum 5 day autonomy. So battery capacity = 160 wh x 5 days = 800 wh.

Next step is to find panel wattage required. To do that we have to select charger type either being PWM or MPPT. This is the step where efficiency comes into play and is taken into the calculations. TO have 160 watt hours of usable energy you have to generate more than that to over come the losses. For PWM, the system at very best is 50% efficient, and MPPT 67%. So the formula for PWM is Panel Wattage = [Daily wh x 2] / Sun Hours. So [160 wh x 2] h sun hours = 80 watts. If using MPPT the formula is Panel Wattage = [Daily wh x 1.5] / Sun Hours. So [160 wh x 1.5] / 4 Sun Hours = 60 watts.

As for charge controller current with PWM Charge Current = Panel Imp current. A 80 watt battery panel should have a charge current of roughly 80 watts / 17 volts = 4.7 amps. For MPPT Charge Current = Panel Wattage / Battery Voltage. For this system 12 volts is selected. So for MPPT 60 watts / 12 volts = 5 amps.

No you determine battery AH. Battery AH = wh capacity / battery voltage. Earlier we found we need a 800 wh battery. So 800 wh / 12 volts = 67 AH battery.

Armed with that you can now figure your question out. I will get you started and tell you 12 volts x 88 AH = 1056 Watt Hours.

[J4mie82]

First thing to do is DO NOT WORK IN AMP HOURS, use watt hours, then convert to amp hours on the last step once battery voltage is selected.Secondly you have to factor in efficiency for either PWM (2) or MPPT (1.5) charging.OK lets say you want to run that TV for 4 hours per day, and you have a minimum 4 Sun Hour day, and the TV uses 40 watts. 40 watts x 4 hours = 160 watt hours. To find the battery capacity needed you want a minimum 5 day autonomy. So battery capacity = 160 wh x 5 days = 800 wh.

Next step is to find panel wattage required. To do that we have to select charger type either being PWM or MPPT. This is the step where efficiency comes into play and is taken into the calculations. TO have 160 watt hours of usable energy you have to generate more than that to over come the losses. For PWM, the system at very best is 50% efficient, and MPPT 67%. So the formula for PWM is Panel Wattage = [Daily wh x 2] / Sun Hours. So [160 wh x 2] h sun hours = 80 watts. If using MPPT the formula is Panel Wattage = [Daily wh x 1.5] / Sun Hours. So [160 wh x 1.5] / 4 Sun Hours = 60 watts.

As for charge controller current with PWM Charge Current = Panel Imp current. A 80 watt battery panel should have a charge current of roughly 80 watts / 17 volts = 4.7 amps. For MPPT Charge Current = Panel Wattage / Battery Voltage. For this system 12 volts is selected. So for MPPT 60 watts / 12 volts = 5 amps.

No you determine battery AH. Battery AH = wh capacity / battery voltage. Earlier we found we need a 800 wh battery. So 800 wh / 12 volts = 67 AH battery.

Armed with that you can now figure your question out. I will get you started and tell you 12 volts x 88 AH = 1056 Watt Hours.

Thanks for the help!


I am using pwm so...

80watt panel at 50% efficiency with 4 hours of sun =

(80/2) x 4 160 watts

The tv consumes 40 watts per hour

160/40 = 4 hours

The battery is 88 ah and can be taken down by 50% capacity (44 ah) safely.

So..

44ah x 12v= 528 watts

528/40 (tv consumption) = 13.2 hours

+ 4 hours extra from solar recharging = 17.2 hours ?

[Sunking]

Thanks for the help!


I am using pwm so...

80watt panel at 50% efficiency with 4 hours of sun =

(80/2) x 4 160 watts

The tv consumes 40 watts per hour

160/40 = 4 hours

The battery is 88 ah and can be taken down by 50% capacity (44 ah) safely.

So..

44ah x 12v= 528 watts

528/40 (tv consumption) = 13.2 hours

+ 4 hours extra from solar recharging = 17.2 hours ?

Yep 3 days.

[J4mie82]

Thanks for the help!

Was a lot easier working with watt hours. I have set up a small tv, a water pump and a couple of Led lights on a boat and was constantly bringing the battery home to charge. I have just installed a small watt meter to help measure what is actually going into the battery. I have got a wind turbine to but struggling to install it on a small fibre glass boat. Do you think I will need the extra power or will the 80watt solar panel ne sufficient. I only use the boat at weekends max 3 days so it has all week to try and charge the battery back up.

[Sunking]

I would not mess with a wind turd myself. The panel should be more than enough to meet your needs. Does your boat have an engine with an alternator? If so you can use a battery isolator to charge the house battery whenever the engine is running. An alternator can do more chargin gin 30 minutes than th epanel can do in a week and get you out of a pinch real fast.

[J4mie82]

I would not mess with a wind turd myself. The panel should be more than enough to meet your needs. Does your boat have an engine with an alternator? If so you can use a battery isolator to charge the house battery whenever the engine is running. An alternator can do more chargin gin 30 minutes than th epanel can do in a week and get you out of a pinch real fast.

I looked into getting an isolator to charge the battery but the problem I have is the main battery for the motor is an old car battery that is only holding charge of 10.5v it still miraculously starts the engine. I have another battery I will swap it with but it is still another car battery with 35ah and only holds a charge of around 12.6v

I'm not sure if the alternator over charged the last battery to death not had the boat long. I thought the battery's had to be if a similar capacity and charge otherwise the good lesiire battery I have will end up charging the motor battery that struggles to hold a charge?

[Sunking]

Use an Electronic Isolator. It isolates the SLI and House battery. Both are 12 volt setups I assume? It can actually get you out of a pinch if your SLI battery were to die, you can bypass the Isolator and start with the house battery in an emergency.

[J4mie82]

Use an Electronic Isolator. It isolates the SLI and House battery. Both are 12 volt setups I assume? It can actually get you out of a pinch if your SLI battery were to die, you can bypass the Isolator and start with the house battery in an emergency.

Would this be ok? Seems a bit cheap tho compared to others?

[J4mie82]

Could I swap the motor battery with my lesuire battery for a while to charge it up with alternator?

[Sunking]

Could I swap the motor battery with my lesuire battery for a while to charge it up with alternator?

Certainly if you want to go to that much trouble.

Only issue might be is available Cranking Amps. SLI batteries (starting, lighting, and ignition) are constructed differently than hybrid and deep cycle batteries. SLI batteries use thin plates to enable them to be able to supply very starting current for the motor, then be quickly recharged So short quick burst. However thin plates do not tolerate deep discharges and recharges very well as it eats away at the thin plates and do not last long if pushed into cycle service

Hybrids and deep cycle have fewer but much thicker and heavier plates. Great for deep discharges, but the battery has higher resistance than its SLI brother, and that means much less high current capability which is not conducive with starting an engine. But don't get excited about it.

I take it you are from UK because you use the term Leisure Battery. Well sorry about that, I won't hold it against you. What that really tells me is you have what we call a Hybrid Battery. A Hybrid is a cross between a deep cycle and SLI battery. It tries to be both and does a fair job of both, just not as good as their counterparts. Will not deliver as much cranking current as a SLI but last longer. Will not last as long as a Deep Cycle, but can deliver high current. Here in the USA the hybrid battery is sold under various Marketing names like:Golf Cart battery, Floor Machine, RV, and Marine Deep Cycle as examples.

So your Leisure battery is a hybrid in my terms and is 88 AH taking over for a smaller 35 AH SLI will be no problem. Sounds like that engine is pretty small. You will know right away, when you swap them crank the engine up. If it starts normally you are OK. If it drags or slow turning means not a good idea.

Disclaimer here. I am not a boat person. I am going to ping another member name Chris Olson to chime in. He knows boats and boat electrical systems and might redirect with better Marine practices. Sad because I am a former Navy man myself on a U-boat. Seems I recall him chewing on me one day. Something on the lines of using heavy mechanical switches to switch in/out house batteries. Not sure how that works or how it can be done safely. Anyway wait for him to respond and see what he says.

[ChrisOlson]

What you really need on your boat when you have a dual battery system (starting and house) is a ACR.

The ACR prevents your loads from discharging the reserve battery system (usually starting). The reserve battery system is used for vital loads like engine starting, navigation or communications (called SLI by Sunking). What this thing does is that when you start the propulsion engine(s) it monitors the voltage on the starting bank. When it rises to 13.2-13.4V it connects your house battery to the system and starts charging it as well. The engine(s) alternators will continue charging the house battery unless the voltage falls back below the set point, then disconnect the house bank.

Your battery selector is a totally different switch. It is used on larger boats to manage dual house banks, plus reserve (or starting). This is always done manually and I recommend installing a Bogart TriMetric or PentaMetric if you are living aboard or cruising, as the battery monitor will tell you the condition of your battery banks. The battery selector allows you to use one or both of the house banks for emergency engine starting in the event your reserve (or starting) battery is dead.

It sounds like your boat is smaller and much simpler, so like Sunking said just use the solar panel to charge your house batteries and keep your loads lit. And install a ACR for charging with the engine's alternator. And you should be good. Under no circumstances go to sea with a starting battery that is in bad shape. Even though your Yanmar diesel might have a hand starter on it, they are NOT easy to start with that.

On the wind turbine deal, they can work OK at sea if you position the turbine to catch the air coming off the Main. The genoa straightens the air for the main'sl so it operates at higher efficiency and better lift. That air flowing over the convex side of the Main is laminar and wind turbines really good when they're in that air stream. The problem with this, obviously, is that 90% or more of your sailing at sea is on a reach and sometimes you're on a port tack and sometimes a starboard. So the wind turbine is never in the right place.

[Sunking]

OK Chris educate me on ACR. Sounds like a expensive Battery Isolator with SMARTS?
Or a Marine version of an Automobile Battery Isolator that cost more, salt air rated, blah blah?
What am I missing here?

There are two ways to connect a battery. Some are better than others.

1. Mechanically with heavy switches and copper cable and damn the consequences old school style.
2. Electronically through silicon (melted sand that is high on dope) sand and smarts.

So WTF is ACR?

[ChrisOlson]

Oops! ACR = Automatic Charging Relay. I think they probably do the same thing as automotive ones. Except the marine ones work both ways so if you have a solar panel on your boat and it is charging the house battery, it will connect the starting battery to top it off too, as well as work the other way. It also disconnects the house battery regardless, within milliseconds, in the event you go to crank the engine to prevent voltage drop to sensitive electronics in your boat that are running off the house battery.

The other difference is probably all the ratings that marine stuff has to have, and be ignition protected, etc..

[Sunking]

Oops! ACR = Automatic Charging Relay. I think they probably do the same thing as automotive ones. Except the marine ones work both ways so if you have a solar panel on your boat and it is charging the house battery, it will connect the starting battery to top it off too, as well as work the other way. It also disconnects the house battery regardless, within milliseconds, in the event you go to crank the engine to prevent voltage drop to sensitive electronics in your boat that are running off the house battery.

The other difference is probably all the ratings that marine stuff has to have, and be ignition protected, etc..

OK I get that part, but is it mechanical using contacts to make connections or through semiconductors?