Alternator choices

[john61ct]

I've heard only of such setups wired to a momentary push button switch

for momentary loads at a high voltage, like starting or a bow thruster

rated for only a few minutes use at a time

then immediately returning to constant use and charging at the lower voltage.

Standard setup for racing, trucking, farm equipment.

But would need an electronics geek, a solid design and specialized parts to go the other way.

Not so easy.

[john61ct]

Even the design for manual switching does not seem straightforward,

why I ask for links.

[Pizzazz]

There are solenoids rated for continuous duty at high amperage. See the link below. Here is how you can make it work with three solenoids and a relay.

Battery A and B.
A- to ground
A+ to house loads
B+ to A+ via solenoid 1 (usually on, off when charging)
B- to A- via solenoid 2(usually on, off when charging)
B+ to 24V alternator, permanent
B- to A+ via a solenoid 3 (usually off, on when charging)

Solenoid 3 switching is connected to ground and alternator output (24V solenoid)

Now, you need a small relay connected to the ignition switch that inverts, i.e. it is off when the ignition is on and on when the ignition is off.

Discharging: Ignition is off, solenoids 1 and 2 are on, solenoid 3 is off, the batteries are connected in parallel. This is when you discharge the batteries.

Charging: Ignition is on, solenoids 1 and 2 disconnect. Then you start the engine, solenoid 3 sees 24V, closes and connects the batteries in series. While the batteries are being charged, battery A could still supply house loads if needed. It may help to rotate batteries A and B every couple of months.

Only solenoid 3 needs to be high current, solenoids 1 and 2, should be sized to the largest house loads. This system will draw 0.2A while the batteries are being discharged. This can be avoided if normally on solenoids are used (harder to find). Total cost around $150.

Continuous Duty Solenoid SPST 12V 200A - Cole Hersee Australia

[john61ct]

Wow, thanks. Bookmarking FFR, came across this in my DB

http://www.gonefcon.com/trucktcom/parallel_sw.htm

Also a ref to Yandina TrollBridge, from the inventor of the combiner VSR.

Memory isn't what it used to be.

[dkenny64]

or feed the 24v Alternator out into a MPPT solar charge controller..
all that would be need would be control the alternator for max output without overheating..ideally a feedback from the amount of current going into the batteries to reduce the alternator output when the batteries are charged..


shouldn't be that hard..


-dkenny64

[Trawlerman]

As regards the comment:


"But remember under full load and in a small engine room even a hot rated alternator may go above 100 degrees C and its output current will be reduced by 50% by the external Balmar regulator - but its charging voltage will remain the same."


This is simply not the case. You can't maintain a charging voltage and simply reduce the current. The battery at a given state of charge will look like a resistive load to the alternator (the lower the battery charge, the lower the resistance), and the current will simply follow Ohm's law of Current = Voltage div. by Resistance. It may be that you meant that the final setpoint voltage will remain the same, and that is true.

[georgeg305]

Before you buy a new high output alternator, Please don't forget that for Lead Acid batteries, the max input the battery bank will accept is based on the bank size. The conventional wisdom is that the alternator output in amps should be about 25% of the storage capacity in amp-hrs. I.E. 200 amp hr capacity will match a 50 amp alternator. You should have a 400 amp hr battery bank for a 100 amp alternator. A Bigger alternator wont hurt anything, just is a waste of money. Battery input current is also a function of state of charge. I.E. a badly discharged battery will accept a greater inrush of current initially but will rapidly decrease as the battery voltage builds back up.
My suggestion is to buy a battery monitor and observe the amperage going in. To force in more amperage one needs to turn the voltage regulator up so you have more than 14.2 volts coming out. That is NOT healthy for the batteries.

[john61ct]

Originally Posted by Trawlerman

As regards the comment:


"But remember under full load and in a small engine room even a hot rated alternator may go above 100 degrees C and its output current will be reduced by 50% by the external Balmar regulator - but its charging voltage will remain the same."


This is simply not the case. You can't maintain a charging voltage and simply reduce the current.

Of course you can, with the right external VR, that is the whole point of spending hundreds on one.

[john61ct]

Originally Posted by georgeg305

Before you buy a new high output alternator, Please don't forget that for Lead Acid batteries, the max input the battery bank will accept is based on the bank size. The conventional wisdom is that the alternator output in amps should be about 25% of the storage capacity in amp-hrs. I.E. 200 amp hr capacity will match a 50 amp alternator. You should have a 400 amp hr battery bank for a 100 amp alternator. A Bigger alternator wont hurt anything, just is a waste of money. Battery input current is also a function of state of charge. I.E. a badly discharged battery will accept a greater inrush of current initially but will rapidly decrease as the battery voltage builds back up.
My suggestion is to buy a battery monitor and observe the amperage going in. To force in more amperage one needs to turn the voltage regulator up so you have more than 14.2 volts coming out. That is NOT healthy for the batteries.

Some lead banks can absorb 1C no problem, others no more than .15C.

But yes, that will not significantly reduce overall 6+ hours of charging time required to get to 100%.

But in a PSOC regime could get you to 85-90% in half the engine runtime.

[evm1024]

Originally Posted by john61ct

Of course you can, with the right external VR, that is the whole point of spending hundreds on one.

You are both right and both wrong (respectfully).

Batteries of any chemistry are not simple resistors. They do have an internal resistance and ohms law prevails.

For any given SOC:

in Constant Voltage mode the power supply must supply enough current such that the supply is voltage limited. If the supply cannot supply enough current to meet ohm's law then the voltage drops.

in Constant Current mode the supply raises the voltage until the current limit is met. THis assumes that the supply can raise the voltage to some unkmown but greater than needed voltage.

Of course the above definitions assume a supply with a very low internal resistance and with huge power capabilities i.e. the supply is not the limiting factor.

In reality our power supplies (alternators, solar etc) cannot raise their voltages beyond a (close to battery voltage) limit because they also have an internal resistance that limits the power that they can supply. ohm's law rules again. Thus our supplies are current limited to start with.

As an example I can limit the current that my Xantrex SW3000 will supply. I have 700 AH LiFePO4 for a house bank and the Xantrex does not have a setting for LiFePO4 (e.g. 13.8 v).

When the bank is somewhat discharged (not near the upper knee) I can set the inverter/charger to supply 100% of the available current. The bank voltage rises as the current remains the same (as the battery charges).

At some point the bank voltage gets close to 13.8 volts (and the I/C does not have a voltage set limit at 13.8). At this time I set the current limit to something less than 100%.

When I do this (set the current to a lower value i.e. drop the current) the bank voltage drops. It does not stay the same. Sure it dances around a bit as the internal bank resistance stabilizes (non-linear and set by SOC, voltage, current and the phase of the moon). Ohm's law.

Eventually I've lowered the current limit on the xantrex low enough such that the xantrex is in effect in absorption. Then of course I shut the I/C down because even at the "low" amperage set point the voltage will rise into the knee.

[Rotten Ricky]

A special vote of thanks to EVM1020 for the excellent professional advice he gives us on this forum - on subjects that he has probably repeated 100 times! Thanks for your patience with the rest of us! It is hugely appreciated!

For the rest of us - the brand-new Universal M35B (Kubota-based) diesel I recently installed was fitted (to my astonishment, and according to auto-electric shops) with a cheap, 60-amp auto alternator used in Kia and Hyundai cars, in spite of them claiming it was a "marine alternator"!

I swapped it for a used (but tested) $50 GM CS144 alternator from a wrecker, formerly usually used on ambulances, police cars, trucks and higher end GM cars like Cadillac. Note that it is usual for an automotive 140 amp alt like this to be de-rated by about 40% for marine duty, so I now have a 100-amp alt. Now this will not be the ultimate in generating DC but it will be a lot better, and I think will be a great bang for the buck - but I have not had it installed long enough to prove it.

The reason I went with CS144 is that they have an excellent reputation for reliability and durability and yet they are simple and easy to work on, inexpensive to buy and inexpensive to obtain the widely-available parts. At these low prices it is a fairly painless matter to carry a (tested) spare alt. They are slightly larger-framed than the usual alts and have a superior fan and as a result have better cooling because of larger internal air gap spacing. This same alt. case is often used in rebuilt 200 and 300 amp alts. - but obviously with much higher rated rectifiers etc.

As to why the obsession with upgrading alts? It depends on many factors about how they are used - how long they can be run before sailing starts, what capacity and what type of batteries, how long it will be before returning to shore-based charging what other source of charging is happening, what speed of rotation etc.

An important advantage of the true marine alt. is that it is built to produce power at lower RPMs. Most diesels turn FAR too slowly for optimum generation in common alts. and this slow speed does not allow the alt, to generate at capacity or the fan to cool the alt. enough, leading to it burning out! If you have an auto-based alt, please try to increase the speed of your alt. by at least 50%. In most cases the driven alt. sheave is already at its smallest diameter, so increasing the crankshaft driver is necessary - and also the water pump to ensure that it does not over-speed and cause cavitation.

So it is not an easy fix. But you can buy kits that use a serpentine belt that will decrease the alt. sheave and increase the crank sheave by slipping a larger hollow sheave right over the existing one. And provide the needed larger water pump sheave. The serpentine belt is smoother, quieter, produces less rubber dust and will drive bigger alternators that would otherwise need a double V-belt. Producing approx. 80-100 amps and more seems to need the extra driving ability.

Another important factor is the ambient air temp in the engine vicinity, etc. The mounting bolt pattern was almost the same as other common alts, but in my case, because I had the room, I opted to arrange to mount the alt further away from the engine block to reduce the added heating effect radiating from the engine itself and it will also allow better air flow through the alt. Installing some kind of heat shield between the engine and alt. also helps.

One should also have good ventilation of the engine compartment. I am trying out a couple of 4" ducts powered by a couple of computer fans, having removed the extremely noisy, hungry, in-line fan that was previously used. At about 100 cfm combined, I hope that these new fans will do the job better at about 1/10th the power use - and quietly. It is not so much of a problem when the engine is running, but the lower consumption, and noise after engine shuts down will be appreciated. I have also made sure that the air intakes are the other side of the compartment to ensure good cross-flow of air.

Good luck with everyone's efforts. The more you dabble in these things, the less helpless you are WHEN something goes wrong! RR.

[Dockhead]

Originally Posted by Rotten Ricky

A special vote of thanks to EVM1020 for the excellent professional advice he gives us on this forum - on subjects that he has probably repeated 100 times! Thanks for your patience with the rest of us! It is hugely appreciated! . . ..

I'd like to second that.

There are a lot of people on CF with a lot of knowledge, but those who are both very expert and who are at the same time patient and articulate in explaining things to others, and who don't go ape when someone with less expertise contradicts them, are especially valuable to the community

[evm1024]

Wow, my head is spinning.

Thanks for the kind words.

[preventec47]

I would like to ask if when the battery banks are full and there is no need
for any charge from the alternator, is the alternator still putting a load
on the engine and if it is a large alternator as discussed... is it approx a
3 hp load even when no charging is taking place ? I would hope that
the pulley on the alternator is spinning freely when it is not outputting
electricity..... and that the load on the engine progresses incrementally
as the charging goes up.

[Rotten Ricky]

Originally Posted by evm1024

Wow, my head is spinning.

Thanks for the kind words.

Yo' welcome - it is deserved!



But is yer head spinning fast enough to prevent the previously mentioned heat overload...?


Thanks, RR.