Size of Battery Charger

[zboss]

Originally Posted by colemj

What size engine do you have? A 200A alternator is going to require a serpentine belt and will lug down smaller engines. If your engine is less than ~75hp, you may want to research this a bit if it is to be a primary charging method.

Mark

Good point... I did know about the serpentine belt. Didn't take into account the engine size. This is why I posted here... to get feedback like this.... thank you!

We have a 46.

[pbiJim]

Volts times amps = watts.
746 watts = 1hp.
Some people here on this board have claimed that alternators are roughly 50% efficient. I don't know where that 50% number comes from, but assuming that it's true & rounding things off a little:

200amps x 12v = 2400 watts.
2400w/750 = 3.2hp.
3.2hp / 50% efficiency = about 6-1/2 hp used to produce 200 amps via the alternator.

[zboss]

Originally Posted by pbiJim

Volts times amps = watts.
746 watts = 1hp.
Some people here on this board have claimed that alternators are roughly 50% efficient. I don't know where that 50% number comes from, but assuming that it's true & rounding things off a little:

200amps x 12v = 2400 watts.
2400w/750 = 3.2hp.
3.2hp / 50% efficiency = about 6-1/2 hp used to produce 200 amps via the alternator.

So, what you are saying is that we would loose about 6.5 HP when motoring?

[Saltyhog]

Assuming the 50% efficiency number is correct, and I doubt it's quite that bad especially for the new hairpin wound alternators from Balmar. Anyway, it would be pulling that from the engine for only a short while. Two things will cause the draw from the alternator to go down. Assuming an external regulator as that's the *only* thing that makes sense here. 1) Your batteries won't draw that much for very long. Even AGM's could only draw that for less than an hour assuming you needed to put 200AH back in them. During the absorption phase, current will go down. 2) The alternator will not supply that kind of current for very long before getting hot. The regulator then will (or at least it should) dial down the output so that it runs within it's temp range.

What made you change your mind from the Solbian solar to the Keyocera?

[zboss]

Originally Posted by Saltyhog

What made you change your mind from the Solbian solar to the Keyocera?

We really want solbian... we had planned the solbian through our heads over and over. Price wasn't an issue until we started looking at the charging system as a whole. I wasn't counting on needing a charger that size, or expensive batteries, etc... so, something had to give. The budget is only so big and we really want our fridge. For the same dollars required for 50 watts of solbian, we can get 280 watts of kyocera, even with the mounting hardware.

We will mount the solid panels on the rail for now, then maybe next year add the solbian to the dodger and bimini. Hopefully, prices will be better.

[goboatingnow]

Originally Posted by sailinglegend

I think Cpt Pat's post that you shot down was absolutely correct.

Peukerts effect does apply during charging but it is impossible to calculate or quantify. So a lower (AGM) Peukert value makes charging more efficient.

Any increase in charging efficiency during bulk stage must be worth having - especially if running an engine or generator.

FLA batteries NEED decent charging facilities and NEED to get back to 100% regularly - but many boaters don't bother - just equalize later. If an owner appreciates these points then AGMs (Lifeline's can also be equalized) are very good for him.

Some quotes from the SmartGuage.co.uk site:

There are 3 separate effects that combine to produce Peukert's effect:-
A. The resistance of the battery due to the interface between the plates and the electrolyte.
B. The resistance of the electrolyte itself and......
C. The bulk resistance of the electrolyte due to the bubbles being produced within it.
These three effects combine to produce the overall Peukert's exponent for a particular battery.

The three effects also apply during charging. But they are impossible to calculate because of the way charging causes the chemicals reactions to take place. Yet the effects can be dramatic.

Sheesh

Peukert's law, presented by the German scientist W. Peukert in 1897, expresses the capacity of a lead–acid battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases.

The Peukerts effect ( decreasing capacity with increasing discharge current ) is partially a result of slow electrolyte dispersal/diffusion and partially a result of an internal resistance that varies as a function of the discharge rate.

LA recharge characteristics do not follow Peukerts law, this is clearly observable by the significant differences between LA charge and discharge curves.

dave

[sailinglegend]

Originally Posted by goboatingnow

.........Peukert's law, .... expresses the capacity of a lead–acid battery in terms of the rate at which it is discharged. As the rate increases, the battery's available capacity decreases.

Again only partly correct.

Peukert’s law says that the apparent Ah size of a bank changes depending on the current draw.

A bank is designed to deliver a capacity with a current discharge that will flatten the battery in 20 hours. (The 20 hour rate). So with a 100Ah battery, a 5A load will flatten the battery to 10.5v in 20 hours.

When drawing currents higher than 5 amps the "apparent" bank size will be much smaller, so the bank will not last as long before it needs re-charging. Conversely when using much less than 5 amps the bank size will apparently be larger and will deliver more Ah.

If a 100 Ah that battery has a Peukert value of 1.25, then higher or lower loads than 5 amps will change the actual capacity of the battery by the following amounts.

With a 10A load for 20 hours there are only 84Ah's available in the 100Ah bank.

With a 1A load for 20 hours there are 150Ah's available in the 100Ah bank.

This just one good reason for joining two banks together.

Originally Posted by goboatingnow

LA recharge characteristics do not follow Peukerts law, this is clearly observable by the significant differences between LA charge and discharge curves.

As I said it is impossible to calculate or quantify the Peukert effect during charging. The difference between charge and discharge curves has lots of other chemical reasons.

[goboatingnow]

There is no peukerts law for recharging , there never was. Sheesh

Dave

[colemj]

If you charge too fast or too long, the smell might cause you to Peukert.

Mark

[pbiJim]

Originally Posted by zboss

So, what you are saying is that we would loose about 6.5 HP when motoring?

Yes, if the bank is drawing the full 200 amps.

If the bank is drawing 100 amps, then you would loose about half as much hp.

Also, I agree with Saltyhog. The 50% number sounds a little worse than I would have expected too. I'm just going with the worst case scenario based on the worst estimation that I have received because I have no accurate efficiency coefficient to work with & the person who threw out the 50% number generally posts good information on this board. I would call those numbers a conservative estimate.

[pbiJim]

Originally Posted by goboatingnow

There is no peukerts law for recharging , there never was. Sheesh

Dave

Are you saying that the peukert's number has no effect on charging what so ever?

Are you saying that there probably is no close correlation between that number & any charging characteristic?

Are you just saying that the number is not an accurate indicator of charging characteristics, so therefore can't be used in any accurate calculations?

Did you mean something else?

[goboatingnow]

Originally Posted by pbiJim

Are you saying that the peukert's number has no effect on charging what so ever?

Are you saying that there probably is no close correlation between that number & any charging characteristic?

Are you just saying that the number is not an accurate indicator of charging characteristics, so therefore can't be used in any accurate calculations?

Did you mean something else?

Peukerts law , derived by a German mathematician in the 19th century models the discharge capacity versus discharge current curve of a LA battery.

Its has no meaning , correlation or any anything to the charge cycle. If you wish to argue otherwise , then " bring your best links at dawn" sir !! .

Dave

[pbiJim]

I wasn't looking to argue. I was simply asking for clarification.

Thank you for providing that clarification.

Jim

[sailinglegend]

Originally Posted by goboatingnow

There is no peukerts law for recharging , there never was. Sheesh

Dave

Yes you are right there is no Peukerts LAW for charging but the Peukert EFFECT is present - that was my posting.

It's all irrelevant anyway for this thread as this effect - which can't be measured or made into a LAW is only relevant when you look at the accuracy of Battery monitors. A value for Peukerts can be put in for logarithmic discharge calculations but not for charging. This is another reason why BMs are not very accurate - and get worse as the Peukert value of the battery changes with age. But that's another thread.

[Jeff Millar]

Very complicated this whole battery selection and charging. My summary of what I understand.
1 ) Trojan 6 volt wet cell batteries are the best choice for long distance Cruising Sailboat. And they can be replaced around the World ( at higher prices )
2 ) AGM'S are not the best selection for the World Cruiser and they have a Critical charging procedure to be followed. ( LIFELINE HAS AN EXCELLENT REPUTATION )
3 ) I am very close to buying five ( 5 ) Oddsey PC - 1800 FT ( AGM'S ) for my house bank battery. And yes I have learned that one bank is better than 2.
I am buying Odysset mainly because they will fit in my space ( outside the engine room ) Gulfstar 50.
Have emailed Odyssey requesting direct feed back for the Battery Charger that I need to buy and their detailed charging procedure that I would follow.
If I do not receive a clear reply from Odyssey, then I will not buy their battery.

Rolls 6 volt wet cell Batteries, I understood were the very best for deep cycle, but apparently from what I have read have serious Quality Control problems, and are very expensive.

All my reading on the various sites has me convinced that no battery will last more than 3 years on a sailboat. ( nearly always blamed on improper charging )

The SEARS DIEHARD MARINE BATTERY ( 100 AH ) COMES WITH AN UNCONDITIONAL 3 YEAR WARRANT, AND IS MADE BT ODDSEY and sells for $259. Unfortunately the 100 AH RATING means I would need 8 to 10 of these and I do not have the space.
Otherwise these are the batteries I would buy.

In conclusion seems to me the best battery to buy and best suited for World cruising would be the 6v wet cell Trojan ( T-105 ) RELIABLE AND AVAILABLE ALL OVER.

Please correct me if what I SUMIZE IS NOT LOGICAL.