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Mixing Batteries


SandyD

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2 minutes ago, magnetman said:

How much power does the moth trap use on a daily basis? I would be tempted to bin the lead batteries and put a single small lithium battery on there. If the trap uses more power than you can get from the solar then its a losing battle whatever you do. 

 

 

Not necessarily. As the days lengthen and the sun passes ever higher overhead, the energy collected by the panel will rise and the energy needs from the light will reduce. (Assuming its on only during the hours of darkness.)

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What? 

 

I said " If the trap uses more power than you can get from the solar then its a losing battle whatever you do. "

 

This is a basic fact. If energy out of a battery is more than energy in then you have a flat battery. 

 

If you can cause this to be "not necessarily" so then I'll be an early investor in your scheme as we will be very very rich. 

I was of course referring to daily in/out as can be seen in the first sentence. 

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3 minutes ago, magnetman said:

What? 

 

I said " If the trap uses more power than you can get from the solar then its a losing battle whatever you do. "

 

This is a basic fact. If energy out of a battery is more than energy in then you have a flat battery. 

 

If you can cause this to be "not necessarily" so then I'll be an early investor in your scheme as we will be very very rich. 

I was of course referring to daily in/out as can be seen in the first sentence. 

 

That's a very big "if" you start off with. And even if true last week it might not be true next week, due to lengthening days this time of year. 

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20 watts plus inverter losses, at a guess about 22 watts. Ar 13.5 volts, that is about 1.6 amps. At present, the equinox, and if it runs all night that = 12 hours x 1.7 amps = 21 Ah to an absolutely flat battery (the inverter would probably cut out on low voltage long before that). During the shorter day months, the discharge would be worse. No wonder the 18Ah battery has suffered.

 

Ignoring the problem of knowing when the battery is fully charged and getting it to that point, discharging a Battery to a very low level of charge uses up far more of the battery's life than discharging to the level most manufacturers test the batteries.

 

It is increasingly looking like too much taken out and not enough put back in.

 

Edited to correct my calcs.

Edited by Tony Brooks
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8 minutes ago, MtB said:

 

That's a very big "if" you start off with. And even if true last week it might not be true next week, due to lengthening days this time of year. 

 

Obviously as it gets lighter the sun will generate more power into the battery but we are just coming out of the dark phase if the year. 

 

More solar doesn't mean you need bigger battery if your usage is low. 

 

I think the OP probably needs a bigger solar panel and possibly also a smaller battery. 

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11 minutes ago, magnetman said:

 

Obviously as it gets lighter the sun will generate more power into the battery but we are just coming out of the dark phase if the year. 

 

More solar doesn't mean you need bigger battery if your usage is low. 

 

I think the OP probably needs a bigger solar panel and possibly also a smaller battery. 

 

If what we are told is correct and the trap is run all night, I think a larger battery.

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7 hours ago, Tony Brooks said:

 

If what we are told is correct and the trap is run all night, I think a larger battery.

I don't know about moth lamps but would a lower wattage (led?) bulb do the same job? It's still light? And all light attracts insects at night, I know that from camping. 

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1 minute ago, Ianws said:

I don't know about moth lamps but would a lower wattage (led?) bulb do the same job? It's still light? And all light attracts insects at night, I know that from camping. 

 

OR even... a candle.

 

All battery problems erased at a stroke. 

 

 

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7 hours ago, Ianws said:

I don't know about moth lamps but would a lower wattage (led?) bulb do the same job? It's still light? And all light attracts insects at night, I know that from camping. 

 

I agree, and it looks like they are available - at a price Mr Google suggests. I assumed she did have an LED bulb with an 18Ah battery, I could not imagine a compact fluorescent lamp running all night on that battery.

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4 minutes ago, George and Dragon said:

This looks to me like a case where the solar will not adequately charge the battery for much of the year. If I were the OP I'd be looking for a way to swap batteries daily during the winter so that the system always starts fully charged. Unless a UV LED is employed. in which case they might get away with it.

 

That pre-supposes the "small" solar panel is capable of delivering the charge required throughout the year, which I suspect is very doubtful. Otherwise, it is just throwing good money after bad. All we know is that the OP wants to put two batteries together because the small one is not doing what she thinks is should, and she has a small solar panel and controller to recharge them. If she had access to mains power then it would be simple to fully recharge during the day, but that does not seem to be an option, so all that is left is reduce consumption or increase the charge. The first implies more solar and the second either a reduction in lamp on time or change to a much lower wattage bulb.

 

As it seems the OP has not been back, I think that we can assume she has her answer and is trying to muddle along. I hope it works.

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Thankyou for the comments - I only run the trap at weekends (generally only one night so 7 days charging, leaving the battery to charge on the solar all week) often skipping weeks in the winter when it is too cold for manny moths. Regarding bulbs, the bigger and brighter the bulb (in the UV spectrum) the more moths you catch, I used to have a 125w MV trap and know of people with 500w MV!

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34 minutes ago, SandyD said:

Thankyou for the comments - I only run the trap at weekends (generally only one night so 7 days charging, leaving the battery to charge on the solar all week) often skipping weeks in the winter when it is too cold for manny moths. Regarding bulbs, the bigger and brighter the bulb (in the UV spectrum) the more moths you catch, I used to have a 125w MV trap and know of people with 500w MV!

 

 

Had you considered that if you did not have a moth-trap you would probably not be troubled by so many moths that you then need to get rid of.

 

Why are you catching them anyway - is it a hobby ?

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1 hour ago, SandyD said:

Thankyou for the comments - I only run the trap at weekends (generally only one night so 7 days charging, leaving the battery to charge on the solar all week) often skipping weeks in the winter when it is too cold for manny moths. Regarding bulbs, the bigger and brighter the bulb (in the UV spectrum) the more moths you catch, I used to have a 125w MV trap and know of people with 500w MV!

 

OK, that seems better apart from the battery being small as my calculations above show. Putting both batteries together will help, providing they get well charged between uses. If you run the trap for two nights each weekend, then it may still not be really workable in winter. It all depends upon how "small" the panel is. The type Aldi etc. sell at times will certainly be too small. 6 days charging in winter for two nights use may well require in excess of 200 watts of panels. (that is a guess, I have not worked it out). swapping to Lithium battery with suitable charge controller would charge far faster than lead acid from the same solar system, but it costs. Once you are on the boat, you will have to learn to look after the batteries so as you would typically have between 300 and 400Ah of batteries (only half that long term usable capacity) powering the trap from the boat's inverter and batteries would be more realistic - subject to proper recharging.

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