Electrical Assistance For Cruisers In Zihuatanejo / Ixtapa Mex

[Mexbungalows]

Hello I am a retired alternator design engineer (experience of rebuilding in excess of ten thousand alternators and design and manufacture of four phase altenator) (100 amps at dead idle).

mexbungalows@gmail.com

y
tel no. (753) 103-2396

[GordMay]

Greetings and welcome aboard the CF, "El Codo".
I look forward to reading your contributions about alternators & Mexico.

[Ram]

Welcome and nice to see you here- How do you get 100 amps at dead idle??

[btrayfors]

Welcome, welcome, welcome! Sure am glad to see you here. Your expertise will be very welcome, since there is very high interest in alternator power, given:

(1) the increased use of AGMs and other new design batteries which can take a very large charge; and

(2) the increased electrical load aboard many (most?) cruising boats these days, and the concommitant need for larger battery banks and larger charging systems.

If I may be so bold as to solicit your views on one recurring question among my clients: "How do I upgrade my alternator setup at a relatively modest cost?"

High-output alternators are available at very low prices, designed for automotive use. Even marine alternators, such as those made by Leece-Neville, are reasonably priced compared to offerings by, e.g., Balmar.

What are your thoughts about de-rating an alternator (limiting it's output) in order to better withstand the long charging periods at high output onboard cruising boats? One strategy I've seen is to modify pulley ratios so the maximum RPM of the alternator is below the maximum output of the alternator. Another, which I favor, is to program an external regulator (like the Balmar MC-612) to limit the alternator's output to, say, 75% or 80% of its maximum design output.

Sure would like to have your thoughts on these and similar issues.

Thanks so much for being here.

Bill

[Chief Engineer]

Definitely need mor alternator/charging guys on the board.

"El Sparko"

[Mexbungalows]

With regard to how my alternators acheive 100 amps at a dead idle, that is a trade secret I´m afraid, but suffice it to say they have more windings and more diodes (rectifiers).

Without question to best way to increase alternator life and survivablility is to reduce the heat generated within the unit. Many designs such as those based on the Delco 10DN do not have adequate heat radiation area for rectifier heat sinks. Failed rectifiers (either shorted or open) are a prime cause of stator overheating (along with a bad voltage regulator that overcharges - stator heat limit is dependent on wattage as well as amperage.

Even the large frame Ford alternators (many aftermarket manufacturers base their "premium" large frame alternators on this design) do not offer enough rectifier radiation area to maintain rectifiers within a safe level of heat. Very hot rectifiers are extremely prone to voltage transients (like when charging batteries and having a 12VDC R/O unit cycle on and off).

Never EVER operate a large DC motor while an alternator is charging especially if charging heavily. If a different engine (like a generator) needs to be started - it needs its own battery. Do not operate a 12VDC anchor windlass when an alternator is charging. There are ways to get around this like attaching a large capacitor directly to the battery terminal on the motor and correctly attaching an avalance diode such as a Motorola MR2535 (The pricey ZAP STOP) is such a rectifier, but by itself is not enough protection for onboard electronics and the alternator/regulator. Capacitors of 10,000 uf and larger are useful.

Getting back to the alternator overheating (insufficient heat sink area) problem; the use of an EXTERNAL rectifier (the term diode refers to devices rated 3 amps or less) chops a full fifty percent of the heat off the total developed inside the alternator. In reality the stator develops more BTU but when an external rectifier package is fitted the need for the positive heat sink inside the alternator is eliminated and it should be removed and that will vastly increase airflow within the alternator thus cooling it better. The only downsides to an external rectifier package is that it requires a mounting space of around nine inches by ten inches by five inches high. The altenator must be modified to tap into its three stator phase terminals and wires run to thepackage. The positive battery wire is removed from the alternator and moved to the rectifier package and a large ground wire installed to the negative terminal on the rectifier package. The three stator wires running from the alternator to the rectifier package should be twisted so as to negate radiated 12VAC noise.

Greeting from beautiful La Mira Michoacan (near where I live) I checked out the anchorage in Zihuatanejo on Sunday and saw one cruiser at anchor and then went to the marina in Ixtapa and saw perhaps four masts, all of them belonging to craft of 40' and longer. Weather 85 degrees, humidity at the waterfront 65%, skies partly cloudy, wind 5 - 7 kts out of the east, and swells to five feet outside the harbor on the open ocean.

I'm glad I brought all my tools, test equipment, marine wires, heat shrink and terminals because such stuff is almost impossible to find down here. I remember walking onto the dock at the marina in Barra de Navidad four years ago and it was a full month before cruisers set me free :-) When they learned that I had the 4-phase alternator I had to come up with six of them.

BTW one of the unsung discomforts of anchoring off the grid and charging with an alternator is that the engine develops a lot of heat and even more so if engine speed above the just-above-idle "sweet spot" is needed to produce enough charging amperage to make engine operate (fuel consumption) worthwhile. Misery = enduring a salon and galley with a temperature of a hundred and ten after charging batteries and trying to sleep in a broiling stateroom. Slower engine speed for charging therefore is crucial.

Hope This Helps!

[btrayfors]

You betcha! And, thanks for the detailed post.

For me, and I would guess from others, you have answered a biggie question (heat and its deleterious effect on alternators) while, at the same time, raising others which in the environment of a small cruising boat are problematic.

The external rectifier as a replacement for the alternator's internal diodes sounds like a very good heat-reducing idea, and for many cruisers the size 9"x10"x5" wouldn't pose an insurmountable problem, especially if it could reduce the internal alternator heat by 50%.

Question: how much would one of these puppies cost for, say, a 100-200 amp alternator?

Related question: Do you think de-rating an alternator could help much in reducing heat? If so, how much reduction in output would be required to have a good effect....20%? 30%? 40%?

The imprecation to avoid the use of large DC motors while the alternator is charging will no doubt pose substantial problems for many cruisers, especially those whose anchor windlasses are powered by the house batteries (most boats). Typically, one runs the engine when raising the anchor in the morning -- at a time when the house batteries are low and need charging -- to help move the boat over the anchor and navigate thereafter, and to keep the voltage high enough so that the windlass is happy. Most windlasses are under-wired, in my experience as the cable runs are quite long, so the extra voltage from the alternator helps. Also, some of the larger boats have electric cockpit winches or halyard winches, as well as 12V refrigeration (usually only about a 6-7 amp draw when running).

Question: could you explain in a bit more detail how the extra amperage draw -- particularly during the in-rush current period -- actually affects and harms the alternator? Would not a smart external regulator (like the Balmar MC-612 or the Ample Power models) have some mitigating effect?

Got many other questions, but I'll hold them for now. Again, really wonderful to have someone with your background and experience here to help.

Mexico sounds wonderful at this time of year, even with the absence of electrical parts stores. Let me know if I can help in that regard (I'm in the business).

Bill

[GordMay]

I’d echo Bill (btrayfors) comments, questions, and thanks David.

[Mexbungalows]

An external rectifier assembly is available and is good to 250 amps capacity. It's cost is somewhere around $400 which isn't bad considering its lifespan and how much money and trouble it will save.

To resolve the issues dealing with the RLC problem with electrical motors, a capacitor and zap stop must be purchased for -each- motor that is used while the alternator is operating. The capacitor and (MR2535) avalanche diode must be wired in -between- the device switch and motor power terminal. I recommend at least a 10,000 uf cap (30,000 is better) rated at 20VDC. Connect the cap to motor terminals with 10 gauge wire. The zap stop has wire color orientation (polarity) for connection and connect the zap stop exactly as you would to the output terminal of an alternator.

The issues that require this particular regimen are fraught with technicalities but what must be addressed are positive -and- negative voltage transients. A large capacitor dampens a large positive voltage surge, and the avalanche diode or zap stop clamps negative oriented transient voltage spikes.

To prove to yourself that an issue exists, touch one hand to a live terminal on a twelve molt motor and the other to a good ground. No reaction, right? But if you should try connecting your hands, operating the motor and then letting up on the switch you will get blown on your butt with voltages approaching 300 for a few milliseconds. The transient will reflect both positive -and- negative peak inverse voltage phenomenon.

[GordMay]

Can’t the battery absorb the switching surge of a DC windlass motor, protecting the running alternator, without the need for a flywheel diode and/or bypass capacitor?

[Mexbungalows]

Those BOOM-BOOM-BOOM cars that drive around emmitting earth shattering bass notes require placing massive capacitors adacent to the amplifier. One Farad or larger - the biggest systems may employ twenty farads worth of electrolytic caps.

The caps are necessary even though huge 2/0 wire may power the amp - battery response time is not adequate and low frequency clipping occurs.

The ONLY way to eliminate the torture of alt / volt reg devices is to either isolate all electric motors to another battery, or employ the recommendations that I have given.

Sorry

[44'cruisingcat]

Originally Posted by Mexbungalows

Do not operate a 12VDC anchor windlass when an alternator is charging.

Wow, this is a shock! I think most people do this almost every time they weigh anchor.

I have a 115 amp/hour battery mounted right next to my windlass, connected to the house batteries by a 50 amp battery combiner. Will this protect my (small) alternators?

Or should I fit a switch to isolate the windlass battery while I use it?

[Dockhead]

The same question! Running the engine at fast idle while using the windlass is SOP!

[hellosailor]

"Welcome and nice to see you here- How do you get 100 amps at dead idle?? "

No secret to that. Either you using a honking big pulley on a 100A alternator so it puts out full shaft speed and full rpm at idle, or you use a 1000A alternator and enjoy the 10% output you are getting at idle.

Physics.

You can do some amazing things with an alternator, if you design the system from scratch to match up the engine's rpm range to the alternator's rpm range and output curve. But that's not discussed when brokers are selling new boats, or makers soliciting quotes from suppliers.

You do need a "much" more expensive alternator, if you want one that has a high initial output AND a wide speed range, to allow the alternator to charge well at idle while not burning out during extensive high speed runs.

[btrayfors]

Mexbungalows,

OK, I think I get what you're saying re: suppression of potentially harmful transients. Anytime an inductive load (like an electric motor) is turned OFF, the collapsing magnetic field creates large electrical spikes, both positive and negative. The best way to eliminate these and to protect sensitive electronics is either to wire the electronics on a completely separate circuit, or wire a suitable capacitor AND an avalanche diode to the motor terminals. Or both (separate circuit AND cap/diode), especially if they share the same power source (e.g., the house battery bank).

In my own case, most of the potential is eliminated by virtue of having a completely separate start battery and a separate battery bank for the electric windlass. My SSB is wired directly to the 675AH house bank and is therefore "protected". However, I do have a radar and an electric frig motor which share panel wiring with other electronics (not good) and an electric cockpit winch which is wired in upstream of the main DC panel (probably not good).


Most boats I see, however, use the house batteries to run their windlass, usually with long heavy cables running forward from the house battery bank. These would certainly create transients, but I wonder how much "protection" could be expected from the house battery bank itself, since this is effectively a large capacitor. As this is a very common arrangement and since alternators with internal diodes often last many years in such service, I wonder how serious the transient problem really is in practice?

Re: the overheating problem with alternators and the use of external rectifiers, I note in my online research that there are at least two designs in common use in emergency vehicles and marine applications which help keep the heat at bay. These are: (1) the mounting of a "double rectifier" on the outside back of the alternator itself; and (2) the use of a separate rectifier unit such as you described. Happily, these latter are much reduced in price. I found a 420A capacity "external bridge rectifier" for $149, and a 210A rectifier for $109. That's good, because for most smaller boat applications a $400 pricetag would be a show-stopper.

There are a number of "marine alternators" designed for "heavy duty service" in the range of 140-320 amps or more, fitted with "double rectifiers" on the back where it is claimed they will reduce internal heating. Their prices seem pretty good...$300-$500, with the rectifiers but without the needed external regulators.

Sorry to bend your ear, but you've raised some key questions regarding the use of marine alternators which I believe are of very wide interest and concern.

Bill