RC to AH Conversion

[GordMay]

How to increase the charge voltage of your alternator on the cheap
SmartGauge Electronics - Increasing alternator charge voltages.


The diode on the left is the diode that raises the charge voltage. The diode on the right is there for suppression purposes. It should be the same type as the other one. Not all alternators require this diode.

[hellosailor]

Dunno, Gord, isn't that obsolete technology and theory? They say "If your alternator charges at, say, 13.8 volts you may want to increase this in order to get a much higher charge current into your batteries. "

But any modern alternator design (since the 70's) will be putting out 14.3-14.4 volts during the bulk/charge phase, assuming the alternator is turning above idle speed and in it's operating range.

I've been doing a little (more) research into charging systems recently, and found that at least one MPPT controller maker is very intentionally using "more amps, less volts" during the bulk charge phase, intentionally applying only a little more voltage than the battery is at--and converting the rest of their power into amperage, because they've found that "leading" the voltage this way, instead of trying for the traditional 14.4, actually allows a faster charge. They say, it's the amperage that counts more than the voltage. And, an off-the-record discussion with someone at a battery company you'd recognize, confirmed this is a valid approach.

Boosting the voltage may boil electrolyte faster--but it isn't the optimal way to charge the batteries. They need AMPS, and the only way to get that, is to spin up the alternator.

As a side note, multiple sources also confirmed that using pulsed DC (PWM) allows the batteries to charge more effectively than using "pure" DC. Some alternators do one, others the other, no fast rule of thumb to find out. Apparently PWM allows the amperage surge to get into the plates, without boiling electrolyte. If you form gas bubbles in the electrolyte at all--even tiny ones--they block charging. So one way to push more power faster, is to look for a system using PWM. Either directly or from an MPPT controller.

The more I look into it--the more I find out that "old standard charging technology" apparently is being quietly obsoleted, and the folks doing the R&D to get the extra 10% out of systems now...are being very quiet about it.

[Ex-Calif]

This has turned into an incredible thread. Thanks to all for jumping in with experiences.

I agree with the concern about overcooking the batteries with the diode trick so before doing anything like that it might be wise to guage up the system and see what's really going on.

I never really thought about electrical distribution much in a DC system but in my online research I am learning how important it is to have a well thought out system. Where the voltage is sensed and where it is distributed from are more critical factors than I imagined.

[Alan Wheeler]

PWM is used in some of the "better" solar panel regulator designs. It is a way to get a usable current when the voltage has decreased to a not so usable level due to failing light. I think it is a great idea and have not understood why we have not seen standard chargers use this principle. Interesingly, I have a charge controller circuit here that uses PWM for charging from a small 6-8A battery charger. I have never got around to putting it together. Must do and try it some day for fun.

[hellosailor]

Dan-
What's really disappointing, is to see a "three wire" alternator system (meaning, there's one dedicated sensing lead) with the sensing lead tied back to the output directly, turning it into an obsolete "one wire" design. If there's a sensing lead, it should go right to the battery, and if there's two batteries...it needs to run through the A/B switch to one/both of them, possibly using an unused field disconnect lead, or some other simple complication.[sic]
Most of us know nothing about charging systems, so why would boat builders waste money installing more expensive systems that so few would really take advantage of? Can't really blame them.

Wheels-
We don't see PWM being use all the time, because it costs money. Money to implement it, more money for a CPU to add charge profiling like the MPPT controllers do.
It was suggested to me that we can emulate PWM by using a 24-volt alternator and center tapping the output (which would work on a number of AC chargers as well) so as to feed the battery alternating DC pulses, but no one really wants to discuss the competitive advantages and where a 60Hz pulsed DC is as good as a 30KHz DC pulse.<G>

These PWM controllers are essentially a computer-grade power supply, which used to be $200 but is now $25, plus a microcontroller. No reason that they couldn't be sold for $50 *if* someone could ramp up the volume. Small obstacle there.

Meanwhile, the cottage built PWM systems out there, command a price. Ouch. Can't blame them for wanting to earn a living, either.<G>

[colemj]

Originally Posted by GordMay

How to increase the charge voltage of your alternator on the cheap
SmartGauge Electronics - Increasing alternator charge voltages.


The diode on the left is the diode that raises the charge voltage. The diode on the right is there for suppression purposes. It should be the same type as the other one. Not all alternators require this diode.

This is different from inducing a voltage drop on the alternator sense line. A diode on the sense line does not raise the voltage output of the alternator. Instead, it causes the alternator to sense the battery at a lower voltage than it really is and makes the alternator raise its amperage output at its normal charging voltage. The alternator will not exceed its rated amperage or voltage output at any time.

This modification should not really present a danger for overcharging batteries. It only causes an alternator which is normally set to choke back its charge very quickly, to keep that output active a bit longer. In other words, it operates more similarly to the bulk charge phase of an externally regulated alternator. As the battery becomes charged, the alternator will ramp down its amp output as expected. The only concern is that the alternator will not go into a true "float" mode, where the amperage is negligable. That is why I mentioned taking the diode off-line when motoring for a very long time. In real life, it is unlikely that your batteries will be fully charged and you are motoring for a very long time, so a modestly higher amp output will not be an issue.

For perspective, we are discussing a 60A stock internally regulated alternator that will never put out more than 30-40A for longer than a few of minutes and even with the diode in-line will only output 20A for twice as long as it normally would before dropping to lower output. At fully charged batteries, the amperage will drop to 5A or so (this is when overcharging can start, but even then it is minimally an issue).

Mark

[hellosailor]

Dunno, Mark. I freely admit that schematic confuses me, I would swear it is significantly different from several other alternator designs. IIRC from the "12 volt bible" or one of the other handy books, there are some 20 different alternator configurations readily found out there.

A diode frame with 9 diodes in it (not 3, not 6, but 9?) doesn't sound familiar, using three diodes "just" for the warning lamp....Makes we wonder if this isn't something special for Lucas Electronics?

With any moden alternator, putting a resistance in the sense line will NOT raise the charging voltage, since that is clamped at 14.3-14.4 anyhow. while older designs that change their voltage, many since the 1970's use a fixed voltage--and when the sense line says "Battery is low" they simply send out more pulses per second. (i.e. from 100 to 50,000 pulses per second, each pulse absolutely identical.)

There *are* many different alternator and charging system designs out there. I'm not familiar with many of them--but that one smells like a Lucas to me.
< G >

[Alan Wheeler]

The use of the "3" diodes is current sharing, nothing more special than that. They probably can't get anythign of high enough current capacity in a one diode design fro that particular Alternator circuit.
How it an alternator "clamped" at 14.4V?? From my understanding, An alternator can produce much higher voltages than that. It is the battery that does the "clamping". An alternator produces Power measured in Watts. The resistance of the Battery determines what the current will be with the battery maintaining the voltage. I stand to be corrected on this one.

[hellosailor]

Wheels-
"How it an alternator "clamped" at 14.4V?? From my understanding, An alternator can produce much higher voltages than that. It is the battery that does the "clamping"."
Nope. A raw alternator or generator (and the terms are often used interchangeably these days, even if that's incorrect) might work out that way, but in the real world with a REGULATOR in the business...when the alternator output has reached 14.4 volts, the regulator cuts off or cuts down the excitation current and the alternator output immediately falls back towards zero. That's the beauty of regulating an alternator (where you can stop excess power from being made) versus a true generator, where you have to "dump" excess power into a heatsink.

With an older design, there's looser voltage control. And if the regulator fails "off" yes, alternator can go China Syndrome. But there are all kinds of designs out there, with failsafe modes, "heroic" protection circuits, etc. The protection circuits/components are not unique to the alternator business.

In a traditional alternator with a loose regulator, if you disconnect the 'sense' wire from the battery, the alternator will go to full power (which can also mean an unregulated 17V+) and stay there until it burns itself out. With many of the new designs, the regulator also senses an overheat condition--and shuts down the alternator. In fact, some will also shut down if there is an undervoltage (~10V) on the battery, making it impossible to restart from a "really weak" battery, and there are technical bulletins out about that because mechanics are replacing perfectly good alternators when the battery was the real problem. (Of course, some of them have always done that. [g]

It used to be that the term "alternator" was reserved for a gizmo that needed external excitation to start making power, and a "generator" was one with a magnet, that could excite itself. And you could regulate either one by shedding load, but you only an alternator was smart enough to be "throttled back" by a regulator cutting off the excitation power instead. Now...with internal regulators and hybrid designs, you can't tell the players without a scorecard, and no one wants to sell those. :-(