Alternator Regulator

Mmmmm I do not think it would double the current flow but I think we are generally in synch. The actual voltage drop for say 2x100AH batteries losing 10AH each (90% charged) compared with a 1x100AH battery losing 20AH (80% charged) is not that great, see graph below:

Image3.jpg


Also the alternator regulator being voltage sensing, which of course governs its output (current flow), would still tend to quickly limit the current flow at these voltages after the initial surge.

The area under the curve (lowest graph) indicating the actual AH put back into a battery set given a 20AH (30A for 40mins) load:

ChargeAmps.jpg


I just think the amount of increase in current flow would not be sustained and as great as you suggest, because the current flow from the alternator regulator is also non-linnear and the voltage sensing capability of the regulator is quite good (hence alternators increase OP when they detect load fluctuations switched in/out).

Of course the true characteristics of the load would need to be carefully considered if we were to do justice to this debate! Be interesting to rig this up on a bench! /forums/images/graemlins/ooo.gif

This kind of problem led to the development of smart chargers which if we want to keep our batteries as near to 100% as possible must be the better option!

Good to bounce this around..... /forums/images/graemlins/cool.gif
 
Increasing battery capacity can increase charge current. It depends on alternator, but the battery will normally have a maximum charge rate, so two batteries can absorb more total amps at a time, assumming alternator capacity available.

Simply, if a battery will take 30 amp charge, 2 will take 60 amp, but this is now limited by alternator, say 55 amp, allowing for service loads, say 40 amp new charge rate. This is why when people fit more battery capacity and a smart alternator reg, they think the new reg has increased alternator output.

The end of the day, increasing capacity will help, do you need to change anything else, wait and see, then decide.

Brian
 
Of course - But first may I quote a passage from the 12V Doctor's Practical Handbook:

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"even if your boat has a 50, 60 or 80A alternator, its voltage regulator will prevent even modestly high charging rates except during the first few minutes after starting the engine."

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Although off subject and slightly different characteristics; I used to be a rally driver (when I was young many moons ago), we used 70A competition alternators and had an accurate centre zero ammeter (70-0-70). Used quite a heavy starting current to get my engine going due to overlap on cam, but the ammeter did demonstrate the above characteristic, so I do support the statement in the book.

I recall on one event the 4TR box voltage sensing circuit failed and the crew rigged-up a manual switch for the co-driver! Full output manually switched - worked quite well used sensibly, finished the event and got us safely back to UK from France, without cooking the batteries! I digress....

OK, so the graph is a real plot of ammeter readings taken for an hour after starting the (boat) engine. The area under the curve equals AH's, the rectangle represents 20AH (30A x 2/3Hr = 20AH).

The rig comprised a 55A alternator, engine at 1400 RPM, charging 2 x 110AH capacity (each) batteries, both more than half empty at start.

It was somewhat surprising to find that during the first hour, it was charging only a fraction of the daily AH demand and during subsequent hours, alternator output current fell so low that you almost never catch-up!

Anyway, I hope the above adds something to this discussion.

Once again, I support the argument for more intelligent battery chargers! /forums/images/graemlins/grin.gif
 
Halcyon - Yes I agree, in practice more current flow but not double and diminishing!
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Simply, if a battery will take 30 amp charge, 2 will take 60 amp, but this is now limited by alternator, say 55 amp, allowing for service loads, say 40 amp new charge rate.

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As you are experienced in this field (no pun intended and no advertising!) I would be interested to know what in your opinion is the smartest alternator control/battery charger on the market today?

BTW: I do apologise to the OP for delving deeper than required into this thread and hope you have benefited from our discussions! /forums/images/graemlins/blush.gif
 
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But hang on a mo Will ... your now charging twice the capacity so I have difficulty agreeing that you benefit from double ampage .....

[/ QUOTE ]The benefit is very real. If you increase the charging current, you increase the number of Ah restored to the batteries in a given time. At the end of the day, it's all about putting back the Ah which have been used.

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I agree if you increase amps - then charging is faster. BUT Will said double the BATTERY capacity will double the amps and therefore better. I find it hard to agree. If you use xx A/Hrs out of a system then it will be xx/ amps + losses to put back. If you have 2 batterys - then amps are effectively split charging each. So effectively you end up with same result.
 
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If you have 2 batterys - then amps are effectively split charging each. So effectively you end up with same result.

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Good application of one of Lenz's laws(?): "the algebraic sum of currents at a point is zero". (As I recall anyway - it was 1970 when I last studied battery theory!) /forums/images/graemlins/wink.gif
 
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Yes I do understand, I am not being contentious, I like to respectfully consider all arguments and by debating these things I believe I, and of course others, benefit. This is an intersting topic.

IMO adding battery capacity is almost always a good idea (usual caveats) and avoids deep discharging a single battery which can reduce its life.

Adding capacity means you can charge a higher current with the alternator, but surely this is if you have 'manual' or as you suggest 'intelligent' control of charging but often this is not the case. I think I feel a new thread coming on about debating and giving advice - will start it shortly! /forums/images/graemlins/smile.gif

[/ QUOTE ]

Lets take it a little further. There is assumption by some that boat have high ampage alternators. Many in fact do not. Many in fact like me carry on with standard alternators as supplied with engine etc. These range around the 35 - 50A mark - based on car / van set-ups.
This then means that they drop ampage quite quickly when charging up batterys as the voltage of the battery rises. They also have a safe cut-of point based on engines always charging batterys that are usually full charged on a car.

So lets recap - instead of total a'hrs out of one battery ie 20 A/hr and the subsequent higher charge rate allowed because battery voltage is down, we have split that across 2 batterys at 10 A/hr each. This then brings in 2 factors : The charge rate will be depressed because both batterys are in higher state of charge, second the charge will be split across two batterys. Even if you max out - the average alternator is not going to deliver anywhere near some of the amp levels some mention.

It's a fact that most charging actually occurs at low ampage - it's only when batterys are pushed to limits that charge rates climb higher. Boost regulators of course affect this - but even they drop off alarmingly at high levels of charge.
 
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My question was about the second graph, not the third.

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OK - Graph 2 just illustrates the response of a fully charged battery to smaller and greater discharge currents.

It shows a battery will have a faster drop in voltage with higher current. Which generally supports Refueler's argument that it will then accept a higher current flow (due to redcued battery V's) compared with two batteries sharing the load.

We have all gone a bit OTT becasue in real life we would certainly need to fully and better understand the battery type (starting batteries comparitively thin plates etc.) and load characteristics. But at least our debate will enable others to make an informed choice.

What I also applaud is the polite and healthy way in which this debate is being conducted! /forums/images/graemlins/smile.gif
 
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OK - Graph 2 just illustrates the response of a fully charged battery to smaller and greater discharge currents.

It shows a battery will have a faster drop in voltage with higher current. Which generally supports Refueler's argument that it will then accept a higher current flow (due to redcued battery V's) compared with two batteries sharing the load.

[/ QUOTE ]What size battery did you have in mind when you did that graph? Must be very small if a 15A load would reduce the battery to only 15% charge in as little as an hour?
 
Just checked the page of the book it was taken from and it does not give this information, just states results to support the principle. That's why I concentrated on graph 3.

For those that want to check source and other graphs/test data - all taken from "The 12V Doctor's Practical Handbook" graph 2 is shown on Page 203!
 
Emnick
To answer your OP check out this website:

http://www.smartgauge.co.uk/products.html

Having had a cursory look through their technical data, equipment and info provided it seems an excellent source.

PVB - No precise battery info so no empirical data but to illustrate the principle in support of the argument I do, why what are your thoughts? /forums/images/graemlins/confused.gif
 
Well, my thoughts are, as I posted before, that it must be a very small battery to lose 85% of its charge in only 1 hour at a 15A discharge rate.
 
OK but I thought I explained the reason it was shown:
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....Graph 2 just illustrates the response of a fully charged battery to smaller and greater discharge currents.

It shows a battery will have a faster drop in voltage with higher current.

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Is it that you disagree with the above statement? /forums/images/graemlins/confused.gif
 
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