RC to AH Conversion

[Ex-Calif]

I have a pretty good handle on DC load calculations and have recently added some significant loads to the boat. Inverter, fans and a fridge.

We have two AC Delco Voyager batteries rated at 620 RC and will add a third this week. Will split two off for the house and one for reserve/starting.

I calculate the house will have 342 AH using the following formula for conversion of Reserve Capacity to Amp Hours for calculating loads. I will plan on 50% of that available = 171 AH.


Amp/Hours = (Reserve Capacity / 2) plus 16

Also in terms of recharging the batteries from a 60 amp alternator what charge rate should I expect continuous? 15-20 amps? I don't plan on modifying the field settings so let's not go there...

We are probably going to be consuming 4-5 amps max for 6 hours. 30 amps consumed needs to be replenished so if the alternator charges at 20 amps we would need a hour and a half of motoring...

I see solar panels in my future...

[Alan Wheeler]

An unregulated Alt does not charge at a set current. The current is determined by the battery resistance. As the batteries charge is replenished, the resistance changes accordingly and the current decreases. As the battery gets closer to fully charged, the resistance is such that no real current is being sent to the battery anymore, so the battery is never fully recharged. Plus you can not say it will take X time to get the current back in as the current progressively decreases.
Fitting a charge controller also has it's drawbacks. I have been looking into that myself just recently and am of the opinion it is worse to have a charge controller on the alternator than to not have fully charged batteries. It's a delema.
One concern I have of your situation though, you could do well to have the 60A alt changed over to an 85A-90A Alt. The 60 is a little on the small side.

[Ex-Calif]

Alan - All makes sense. Wanted to run it by someone because I seem to have read somewhere that a 60 amp alternator won't really give you 60 amps. That is probably true but 20 seemed stupidly low.

In a parallel battery setup I presume the batteries draw according to thier individual states and overcooking is not a concern.

I also bought a cheapo battery monitor that plugs into a cigarette lighter. 3 lights - red, yellow, green - and the pamphlet says green is above 12.8V. Out on the boat all day today under sail with fans, ipods, Otto and instruments and the house batteries never got out of the green.

The fridge is the killer. Will try that next week.

[Ex-Calif]

Originally Posted by Alan Wheeler

One concern I have of your situation though, you could do well to have the 60A alt changed over to an 85A-90A Alt. The 60 is a little on the small side.

Alan - All makes sense. Wanted to run it by someone because I seem to have read somewhere that a 60 amp alternator won't really give you 60 amps. That is probably true but 20 seemed stupidly low.

In a parallel battery setup I presume the batteries draw according to thier individual states and overcooking is not a concern, especially with only 60A available.

I also bought a cheapo battery monitor that plugs into a cigarette lighter socket. 3 lights - red, yellow, green - and the pamphlet says green is above 12.8V. Out on the boat all day today under sail with fans, ipods, Otto and instruments and the house batteries never got out of the green.

The fridge is the killer. Will try that next week.

I'll keep the bigger alternator option in mind, although I would more likely opt for solar. As weekend warriors with occadional week trips I usually have all week to charge the batteries.

[colemj]

Your 60A alternator will very quickly drop its output to 15-20A during the bulk charge stage and even lower as the battery voltage rises if it is internally regulated. The reason for this is the regulator is a type used for automotive purposes and expects the alternator to be running all of the time and the batteries to be mostly charged. So it rapidly throttles back its output to prevent overcharging.

One thing you might consider is placing a zener diode in the alternator sense wire (make sure to get the direction right). The diode is being used to provide a resistance that causes a ~0.3V drop on the sense wire. This will keep your alternator output higher than its internal regulator normally will keep it. You can hook the sense wire to a switch where the zener is on one side and that will let you choose the "charging regimen" you wish (jump past the zener if motoring for long periods of time, put the zener in-line for normal motoring or battery charging).

No modification of the internal regulator and 50 cents in parts (maybe $2 if you include a switch). Alternator output will stay higher longer and probably cut your charging time by a third. The modest increase in output for a longer time is well within the limits of small-frame alternators, so you won't need to worry about the alternator burning out.

Mark

[senormechanico]

Colemj,

I think you mean Schottky diode.

A zener diode usually has about 0.7v forward drop as does a run of the mill silicon diode and in this case, the Zener characteristics would not be called into play at all.
It all depends how much extra charging voltage you want. A Schottky will add approximately 0.3 to 0.5 volts, whereas a silicon diode will add approximately 0.7volts.

Here's a diagram for putting a diode in series with the sense lead:

(alternator sense connection) ---|<|--- (battery+)

where ---|<|--- is the diode with the cathode end on the left side (it usually has a band marking it). To disable the increased charging voltage you would connect a spst switch across the diode (thereby in effect removing it from the circuit) to revert to normal charging voltage.

This diagram is for the voltage sense connection and WILL NOT work if you put it in series with the Alt + Output lead.

Steve B.
Retired electronics technician

[Sandero]

My own experience with externsl smart regulators with high output alternators is that they do NOT pump out oddles of amps... EVER.

My batts are usually never very low, so this could be one of the reasons... but when they are "down" the most I ever see is 50 amps from a 120 amp alternator and it doesn't hold it there very long, but ramps down and might hold it at 15-20 for a 500 AH bank.

Of course there are many factors... like alt temp and alt RPMs etc., but I never saw those amps pouring out of the alternator.

When the batt voltage is dropping into the 12.3 and lower range lights are going dim and who knows what is not going to work properly so you can't let the batts get deeply discharged.. can you?

Has anyone else seen the amps flowing out at 80 or 90 for any length of time? And what was the circumstances?

jef
sv shiva

[btrayfors]

Jef,

Just back from a sailing trip in Maine aboard my boat, Born Free.

We have 675AH capacity house batteries (six Trojan T-105s in series/parallel). Alternator is a Balmar 100A model, with a Balmar Max-Charge regulator.

I routinely see 80+ amps output during the bulk charging phase after a night at anchor (during which the frig draws about 7A some 70% of the time, plus anchor light, plus cabin lights, plus inverter to charge cell phones, etc, plus bilge pumps, plus radio(s), plus stereos or TV, etc. The output stays somewhere north of 80A for quite awhile until the acceptance charge begins, whence it drops off to 40-50 amps or so, and finally to less than 10 amps during the final charging phase(s).

The amount of charge you see from such a setup is dependent upon a number of things including, inter alia: state of charge of batteries, condition of batteries, wiring adequacy, alternator output capacity, regulator function, temperature, etc.

Bill

[Alan Wheeler]

Steve, will a silicon diode providing a 0.7V drop be too much??

[Paul Elliott]

I get alternator output similar to Bill's. VALIS has a Balmar 110A alternator (I should upgrade this), and a Link 2000R charge controller. My battery bank is 4 AGM 8D batteries, about 1000AH capacity. I also have a seperate starter battery, connected to the house bank through an echo-charge.

I typically run for two or three days with the solar panels (3x 100W) providing the only charge, then run the engine for a couple of hours to make up the difference. I will see around 90A initially, and after about an hour the charging current has fallen to around 70 or 80A. It continues at that level through the rest of the bulk-charge phase.

These numbers were while I was racing, so I was running the engine at 2000 RPM with the transmission in neutral. If I up the RPM, the alternator output will increase a bit. The Link 2000R is able to limit the alternator output, and will slowly ramp-up the current to minimize belt damage. It has worked very well for me.

[Alan Wheeler]

If I up the RPM, the alternator output will increase a bit.

Arrrr yes, a very important issue. Not all Alts are created the same.
An alternator has two specific points in their design. And a manufacturer will have many designs. The two points are RPM where the Alternator cuts in and RPM related to the current it actually generates. Just because an Alt. is spinning, does not mean it is generating. There is a "switch on" point. This point varies from model to model also. It is not just 1000RPM. Some may not swtich on till they reach 1250 or even 1400RPM. Then once it switches on, there is a relation between RPM and current generated. It is not the same for all. One 12V 80A model may generate 15A at 1400RPM for say and another maybe generating 8A at 1400RPM. And the current varies all the way up through the RPM range. So you need to match the Alt. to the engine RPM range. A slow reving engine will want something that switches on at a low RPM and is putting out a good deal of current at a medium speed. A high reving engien will want something that switches on at a higher RPM range and is generating the current at a higher RPM range. The pullies need to match the engine so as the Alt is switched on at idle. If it doesn't switch on, then you have no electric Rev counter by the way.

[colemj]

Originally Posted by senormechanico

Colemj,

I think you mean Schottky diode.

A zener diode usually has about 0.7v forward drop as does a run of the mill silicon diode and in this case, the Zener characteristics would not be called into play at all.

Thanks Steve,

Yes, I did mean a Shottky - don't know why I typed Zener. A 0.7 volt drop is too much for a small-frame internally regulated alternator to handle continually. It would also result in boiling the electrolite when the batteries are mostly charged. It could be used for faster charging, but you would need to pay attention to it. I have found that a 0.3V drop lets me leave it mostly unattended with no consequences (I have it across a switch like you describe and turn it off when I am motoring for long periods - 6hrs or more).

Mark

[Vasco]

Originally Posted by defjef

My own experience with externsl smart regulators with high output alternators is that they do NOT pump out oddles of amps... EVER.

jef,

My experience is totally opposite to yours. I regularly see 90 amps output from the alternator on both my set-ups. One is an Ample Power 3 stage regulator with a 100 amp Powerline alternator and the other is all Balmar, regulator and 100 amp alternator. This is usually after anchoring a couple of days and then motoring. What is your set-up?

[senormechanico]

Originally Posted by Alan Wheeler

Steve, will a silicon diode providing a 0.7V drop be too much??

It depends on a bunch of factors, wiring, battery condition, alternator original voltage output etc., but the easiest way to find out is to measure voltage at the battery when you know it's already charged and the alternator is running at cruise RPM. Installation of the diode in the sense line would ADD 0.7 volts to your measurement.

Steve B.

[hellosailor]

Dan, as Wheels mentions there are design points in alternators. I got literally twice the output from one, by changing the pulley to the proper size for that installation. Someone had previously replaced the original alternator with the present one, making no consideration for the different design operation points. New pulley? Batteries charged up in half the time. Alternator has so much excess capacity it may still run forever. (Knock wood.)

Delco and AC/Delco put their specs online, as do some of the other American companies. An alternator "turns on" at some point, typically 1500 shaft rpm, and makes next to no power until something like 3-4000rpm, and then overloads and burns out somewhere between 8,000 and 15,000 rpm.

So, if you really want effficient charging, you want to start with finding out what engine speeds you will run at. If that is a range from 800-3600 rpm, that's a 4:1 or 5:1 ratio from "idle" to "battle speed", and then you look for an alternator which has a similar operating range (i.e. 5:1) or a wider one.

You could have two very different 60A or 100A alternators. Say, one of them turns on at 1500RPM and the other turns on at 1800RPM, and they're both putting out a whole 20A at that speed. Wow, that means at engine idle, that's all you'd get if you geared up the alternator (meaning, put the right size pulley on it) so it was just starting up at engine idle speed. But...if one alternator was designed to put out full power at lower speeds, and the other designed for a high-rpm engine in a 4-cylinder riceburner...One of them might give you full power at your typical cruising speed (3000 rpm?) while the other wasn't giving you more than half power at that speed.

If you look at alternator output curves online, this becomes REAL obvious, and you quickly realize why there are so many different alternators out there.

The Schottky diode...a nice kludge. The problem is still that the regulator in an automotive alternator is designed for three purposes:
1-Do not overheat the alternator (do not run full output for long periods)
2-Do not overcharge the battery (cut back output very quickly as the battery gets near 90% charged)
3-Try to charge the battery while running the lights and heater motor.

You'll note that charging the battery, is not really a priority.
< G >

Even with properly matching the alternator (so it can loaf along at maybe 50% of its rated output in the overheated engine compartment) it is never designed to get the battery back to 100% charge, which is where the diode trick would be nice.

But with the cost of batteries and fuel...it might be worth considering an external 3-stage regulator in any case, instead of the diode. If you don't feel comfortable with wires, an alternator shop should be able to tap yours for using an external regulator, for maybe $50.

Because those Voyagers are a "maintenance free" (aka "maintenance not possible") design, I'd be more concerned about overcharging them. If you use that diode boost--make Real Damn Sure that the batteries are not being overcharged, you have no way to replace lost electrolyte on them.