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Old 08-03-2013, 12:47   #46
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Re: wiring solar output

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Originally Posted by sailorchic34 View Post
AH No... the Peukert effect is a subtractive effect. You can't get more then 400 amps out of a 400 amp rated hour bank. The Peukert effect reduces the effective amp capacity due to higher amp discharge rates. But it does not work in reverse.

At rest you have a 400 amp hour bank. As amp draw rises the effective capacity of the bank is reduced. The more amps drawn the more its reduced. So a high amp load might reduce the effect amp capacity by 50% or more. Depending on battery type.

AGM has the lowest factor, gel the highest and LA in the middle. The overall effect is the same ratio weather its a 200 AH bank or a 1200 ah bank.

But you never get more amps out of a rated bank then what its listed for. Not in this universe anyway...
This is not the case and why at low loads your battery SOC is not in line with rated Ah capacity and Ah's drawn out of the bank. Peukert goes both ways.

Last time I checked I do live in this universe and have taken well over rated Ah capacity out of batteries both on my boats and in the shop and on the bench while measuring and counting Ah's out. I've done this far too many times to count...

The Ah capacity is based on a specific "rate" or current for the rate eg: 20hour rate, 5 hour rate, 10 hour rate etc..

A 100Ah battery would be drawn to 10.5V with a 5A load. It should take 20 hours at 80F to get to 10.5V. This is a 20 hour Ah rating.

You get there by dividing capacity "C" by 20. So a 100Ah battery supports a 5A load for 20 hours but a 130Ah battery supports 6.5A load for 20 hours...

Apply a 1A load to a 100Ah battery with a Peukert of 1.25 and you'll get more than 100Ah's out of the battery, somewhere around 149 Ah's.....
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Old 08-03-2013, 12:52   #47
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Re: wiring solar output

You are of course right MaineSail, batteries are rated at a particular current, hence if you draw less the effective Ah is greater then specified

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Old 08-03-2013, 12:59   #48
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Re: wiring solar output

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Originally Posted by goboatingnow View Post
You are of course right MaineSail, batteries are rated at a particular current, hence if you draw less the effective Ah is greater then specified

Dave
I know, I am just trying to help Sailorchick with understanding the Peukert effect.. Clearly though I am a just Martian or some sort of alien being ......
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Old 08-03-2013, 17:17   #49
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Re: wiring solar output

Hey I may be from a small planet near Betelgeuse and I'm blonde so what do I know.

I still say weather charging or discharging the Peukert effect is deductive.

See SmartGauge Electronics - Peukert and charging

It also discusses why amp monitoring devices are sort of guessing.

Oh and another link just for fun: Peukert Effect

I do understand, well I think I do anyway, the relationship of the amp/hour rating and battery capacity. With lower amp draw you'll get more time to empty in say a group 27 battery. But you really don't get more watts then the battery amp/hr rating works out to be.

OK maybe I am super dense, If so, sorry, that blonde thingy is a bi**&^...
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Old 08-03-2013, 17:21   #50
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Re: wiring solar output

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Yes if they are not wire appropriately this can happen. I have a number of customers with half the bank on one side of the boat and the other half on the opposite side. Not ideal and I'm not a fan of it but it can be done. Neg goes up port and positive goes up starboard or vice versa. The parallel wiring is then carefully matched lengths of appropriately sized wire. I've not measured any intrabank imbalances on these set ups when done this way. When set up with pos & neg feeds on just one side of the boat I can and do measure intrabank imbalances.
OH see I agree completely with this. My cabling is not balanced which is why I don't run both sets of battery's as one bank. Done correctly its works as you say. But how many boats are done that way....
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Old 08-03-2013, 18:01   #51
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Re: wiring solar output

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Originally Posted by sailorchic34 View Post
Hey I may be from a small planet near Betelgeuse and I'm blonde so what do I know.

I still say weather charging or discharging the Peukert effect is deductive.

See SmartGauge Electronics - Peukert and charging

It also discusses why amp monitoring devices are sort of guessing.

Oh and another link just for fun: Peukert Effect

I do understand, well I think I do anyway, the relationship of the amp/hour rating and battery capacity. With lower amp draw you'll get more time to empty in say a group 27 battery. But you really don't get more watts then the battery amp/hr rating works out to be.

OK maybe I am super dense, If so, sorry, that blonde thingy is a bi**&^...

Thanks, the Smart Gauge link said exactly what I did..

Quote Smart Gauge:
"An often neglected aspect of Peukert's effect is that discharging at lower rates will increase the run time quite substantially. For instance, in our example of a 100 amp hour battery (at the 20 hour rate), with a Peukert's exponent of 1.3, discharging the battery at 5 amps gives us 20 hours run time (so 100 amp hours are actually available). Discharging at 2 amps gives us 66 hours run time. But wait, that's 2 amps for 66 hours, that means the battery has provided 132 amp hours. This is correct.


At lower discharge rates, Peukert's effect means the battery has a higher capacity. This is why it is so important to check the rating on battery specifications. Rating this same battery at the 100 hour discharge rate (instead of the more usual 20 hour rate) would result in a higher amp hours "number" to stamp on the side of the battery, thus making the battery look bigger than it really is. The true capacity is exactly the same.


Discharging this same battery at 0.5 amps would give a total run time of just under 400 hours. That means a total of 200 amp hours were provided by the battery"
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Old 08-03-2013, 18:57   #52
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Re: wiring solar output

Ah I see said the blonde woman. So the peukert equations give you the actual corrected battery capacity. OK Got it..
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Old 09-03-2013, 02:09   #53
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Re: wiring solar output

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....I have combined the two banks into one from time to time and tried just leaving the battery switch in both. I found that I got to 80% SOC faster keeping the batteries separate. That's using solar..........
Maine Sail said:

It is more efficient to charge one bank than two, unless using 100% free energy. Even then, with solar or wind, the time allotted to "finishing" two banks is less efficient due to the longevity of the time the bank spends acceptance limiting and the time the "finishing" charge takes.

I think this concepts needs a lot more clarification, but it is another very good reason why bigger is better.

It takes a bit of simple maths to prove the point, but a 100 Ah battery that is discharged to 50% may accept 30Ah in 1 hour during the boosts stage and the remaining 20Ah in 4 hours during the less efficient absorption phase, a total of 50 Ah in 5 hours. Doubling the battery size (with the same charging source of 30 amps) to 200Ah will accept 15Ah into each battery in 1 hour, but it will take 2 hours to put in 60Ah. The key point is that for two hours it is in the more efficient Boost stage where the battery is taking all the current the charge source can give it. The next 40Ah in the absorption stage, where the current actually going into the battery is falling, will take 8 hours a total of 10 hours. Yes it will take double the time to fully charge the batteries, but note that the initial boost charging stage has captured 60Ah in two hours (an average of 30 amps/h), but with the smaller bank it could only capture 50Ah in 5 hours. (10 amps/h) So a bigger bank will be more efficient and accept more Ah more quickly from all charging sources.

Since a lot of the time we are only charging up to 80-85% then these figures are significant.
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Old 11-03-2013, 20:15   #54
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Re: wiring solar output

Ah but when anchored out and all your charging is done with solar with a maximum of 11ish amps, that ramp up from nothing at sunrise to about 11 amps from 11 am ish to 3 pm ish and then start tapering back down, the difference in charge acceptance rates is not that big a deal.

Oh agreed that a bigger bank will except more current faster. But with solar its not so big an impact. My batteries are topped off by about 3pm most days anyway..
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Old 01-04-2013, 16:34   #55
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Re: wiring solar output

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So is there a best/better/difference on where you wire the solar controller output to in order to supply the batteries? The choices I see are:

1 - directly to the batteries (the hardest considering there are 2 banks)
2 - to the DC panel supply via the DC main panel (seems the easiest)
3- to the alternator supply point on my isolator (makes use of the current selector switches etc)

And for all choices proper breaker/fuse protection and wiring sizing is will be in place.
So I did option #2. Just ran a 6AWG wire from the solar controller to a new breaker I installed in the main DC panel and let the power feed back to the batteries via the supply wire. I figured that wire was already sized enough to supply the whole boat DC loads so why not. Now that it is running I checked the voltages and the voltage leaving the solar controller matches the battery actual voltage.

No only was this easier it saved a few dollars.
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Old 01-04-2013, 17:24   #56
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Re: wiring solar output

I Believe Peukert's constant is about different battery capacity with different rates of discharge. The faster you take the current out of the battery, the lower the usable capacity.
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