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low alternator output current

5K views 19 replies 7 participants last post by  CVAT 
#1 ·
My sailboat has a Westerbeke W30 diesel with a 51-amp alternator with built-in single stage regulator (read "car alternator"). My house batteries are a pair of Trojan T105's. Not a good combo, I know, but due to limited finances right now it will have to do. I have a fridge that draws 3.5A all day long. Couple that with a little music and a little light and I figure my average draw is around 4A tops, so ~100Ah per day. Based on a 5A draw I should get just about 24 hours taking my battery from 100% to 50%.

My problem is that I'm getting nowhere near 51A out of my alternator. The alternator output is connected directly to the load side of the starting battery switch. When I start the engine it settles down to showing a few amps charge as the starting battery never discharges. When I combine the batteries, it jumps up to ~15A, never higher. After an hour or so it'll drop down to about 12A. If I'm drawing 4A and only putting 15A back in during charge, that means I need to run the engine for an hour for every 4 hours of discharge... not really a workable solution. The only thing I can see that looks substandard is the ground wiring on the alternator... I've read that it should be full-size wiring to handle the full alternator output, but it's not, it's rather thin-guage (14ga max) that runs back to a bolt on the engine. Could this affect my alternator output?

When the engine is on and revved up, the starting battery voltage at the panel shows ~13.8VDC. When I combine the house and starting batteries, the voltage drops to ~12.8VDC when the batteries are discharged. It takes literally an entire day of motoring to get the combined battery voltage up to 13.8VDC. I'll measure the voltage at the alternator itself, but I wouldn't expect a 0.6V drop between the alternator and the battery / panel guage... the wiring is hefty, maybe 8ga or 6ga. Maybe my regulator is toast?

Any help greatly appreciated.

Dave
dolce fa niente - CS36T
 
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#2 ·
Your wiring is way too small.

Why go to the start bank when it's the house bank that needs the charge?

Internally regulated alternators work just fine for what you're doing.

Without an external regulator, though, the voltage setpoint is determined by the regulator.
 
#3 ·
t 105's need big wire like 2 or larger. the batteries should draw the full 50 amps from the alternator but your voltage regulator will not let it because it would overheat if it runs there for long. external regulator would let it charge faster but make a short life for the alternator.
 
#4 ·
So, the alternator's rating of 51A is a "peak" or "maximum instantaneous" rating rather than a continuous output rating? What's the point of putting such a misleading rating on an alternator? I guess it's analogous to "cold cranking amps" on a battery, although that is a useful parameter for a battery... not so much for an alternator. They should be rated continuous as any other rating is meaningless.

Just curious here: if the regulator is sensing alternator temp (one figures it should as it's in direct contact with the back of the case so the cost would be absolutely minimal to the manufacturer) then I should get lots of amps out of it when it's cold, dropping down as the alternator heats up to protect it from overtemp damage. I figured the battery voltage was rising as the batteries charged (approached acceptance phase) and (hopefully) that was what was causing the drop in amperage over time, but maybe it's just the alternator heating up and the regulator dropping the current to protect it... the voltage at the battery tells me I was still way deep in bulk phase, or should have been.

Bottom line is I need a bigger, or at least better, alternator. It's too bad that I could buy a decent used car for what it's going to cost me for a 70 or 100A alternator and multistage regulator.

In order to run 2ga I'd likely move the ammeter from the cockpit down by my battery switch downstairs and replace it with a green idiot D+ LED on my panel outside in the cockpit. Would this give me any more amps with this alternator? I'm thinking I may as well do it now as I'll need the upgraded wiring when I eventually put a high-output alternator in.
 
#7 · (Edited)
So, the alternator's rating of 51A is a "peak" or "maximum instantaneous" rating rather than a continuous output rating? What's the point of putting such a misleading rating on an alternator? I guess it's analogous to "cold cranking amps" on a battery, although that is a useful parameter for a battery... not so much for an alternator. They should be rated continuous as any other rating is meaningless.

Just curious here: if the regulator is sensing alternator temp (one figures it should as it's in direct contact with the back of the case so the cost would be absolutely minimal to the manufacturer) then I should get lots of amps out of it when it's cold, dropping down as the alternator heats up to protect it from overtemp damage. I figured the battery voltage was rising as the batteries charged (approached acceptance phase) and (hopefully) that was what was causing the drop in amperage over time, but maybe it's just the alternator heating up and the regulator dropping the current to protect it... the voltage at the battery tells me I was still way deep in bulk phase, or should have been.

Bottom line is I need a bigger, or at least better, alternator. It's too bad that I could buy a decent used car for what it's going to cost me for a 70 or 100A alternator and multistage regulator.

In order to run 2ga I'd likely move the ammeter from the cockpit down by my battery switch downstairs and replace it with a green idiot D+ LED on my panel outside in the cockpit. Would this give me any more amps with this alternator? I'm thinking I may as well do it now as I'll need the upgraded wiring when I eventually put a high-output alternator in.
I don't know of a single alternator that is rated "hot" for its face value current rating. They are all cold rated.

You should see the 51A +/- for a short period of time before it heats up but don't trust a crappy dash ammeter. Use a DC clamp meter or a battery monitor with a REAL shunt...

It sounds to me like you have a blown diode or two. Also voltage sensing on these factory systems is absolutely HORRIBLE. I regularly measure .6V to over 1V of drop between the alternator and battery bank and this WILL lead to low current output.

The charge current should NOT feed to the start battery first especially with a large deep cycling house bank in the circuit. It should feed house bank first, then feed the start bank via the ACR, if you want any level of performance. The idea here is to pass as little current through the ACR is as humanly possible. The start battery will always be almost fully charged and will be taking only a couple of amps, which means very little voltage drop across the ACR and its wiring, and this will also prevent "relay cycling" which can also murder your charge performance......

I would be very, very, very surprised if you killed an ACR... Check the ground wire and fuses. In hundreds and hundreds of these I have yet to see a dead one. Every time I do hear of a dead one, and go to fix it, the thing is only "broken" due to a wiring mishap. While certainly possible I've yet to see it...

The ammeter is certainly part of your problem. It needs to go........ If you want any measure of performance out of your alternator it needs large cables including a dedicated negative, that feeds directly to the house bank with no interruptions other than a fuse in the positive within 7" of the battery rated at 150% of max alt rating.

If you really want to get fancy have an alternator shop set you up for external voltage sensing so you can run a v-sense wire direct to the house bank. Short of this you will need really large wire as even a 3% voltage drop at 14.3V results in just 13.9V at the batteries, and this will drastically hinder charge speed/duration performance.

FWIW I can regularly get these old 51A Mitsubishi alts to run at 36-44A +/- with proper wiring...
 
#5 · (Edited)
You have other "issues" if you've still got an ammeter in your cockpit.

Motorola alternators do not do what you describe. Only Hitachi alternators do that, and they're horrible. Do a search here on Hitachi by Maine Sail and you'll see why.

You might find these interesting:

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

You also don't have to buy a car to get a decent high output alternator and external regulator. You can get a Leece Neville alternator for around $200 http://www.ase-supply.com/Default.asp and a Balmar Max Charge MC-614 for about the same. As I said, you could do without the external regulator for use as you've described if you have a quality thee step charger and your boat and you plug back in when you reach your slip.

Those links come from this topic:

Electrical Systems 101 Electrical Systems 101

Please feel free to noodle around there for more information.

This is another discussion that gets into the ammeter issue with a link to Maine Sail's website:

http://forums.catalina.sailboatowners.com/showthread.php?p=1194183&highlight=ammeter

Dave those skippers had exactly the same issues you describe (especially reply #15). Small world. Read the links in that discussion, some of which I've repeated here (before I found that one).

Good luck.
 
#6 ·
Thanks so much, Stu, for all of the info... I will read it over the next day or two and I'm sure I will learn a great deal.

The electrics on this boat are a mishmash of original 1980's stuff like the cockpit panel with it's analog gauges, some upgraded (nice) stuff like Blue Sea AC and DC panels, ACR, and battery switches, the aftermarket Leece-Neville alternator, good multistage high-current AC charger, galvanic isolator, and a whole bunch of ugly, loose, odd-colored (purple? seriously?) wiring spliced (poorly insulated splices with no shrink tubing or even tape) into the original harness wiring as required. If I had the time, I'd rip it all out and start over... I've had to "fix" quite a few things which had been done by the previous owner.

Just to mix things up a little, I don't have a 1-2-B switch... I have a BlueSea panel unit with a toggle switch for house, a rotary switch for engine, and a rotary switch which connects load side of engine switch to battery side of house switch in order to facilitate starting engine with the house battery. So, can't charge only house battery with this unit as engine switch MUST be on in order for combine function to work (exciter is coupled to starting battery circuit as well). I also have a BlueSea ACR which is kaput... used to work, doesn't any more. It's only rated for 60A, it may have just worn out. On my list to replace but for now it's not a biggie to hit the combine switch while underway with engine on.

My alternator is a Leece Neville 8MR2199K, data sheet description field is "high output alternator". Has BRG2062 regulator built-in which lists set point as 14.3VDC.
 
#9 ·
the diodes are in the alternator not the regulator. they turn the 3 phase AC output of the windings into pulsating Dc current. there are 6 diodes and loosing a few means less output current/ slower charging. adding a Balmar will give you more output but will make short work of the alternator because they are not designed to produce a high current for long periods and will burn out. a new regulator will not fix bad or to small wire
 
#12 · (Edited)
Thank you everyone who has responded. I've learned quite a bit. I have some specific questions to chart my course forward on this electrical shmozzle.

I plan to replace the small-gauge AO POS (+) wire that runs to the cockpit ammeter and back to the start battery switch with a fat cable that runs directly to my house battery positive binding post. The ammeter, I know, needs to go... I don't know much about ammeters but I'm guessing that my 1980's analog gauge is probably fraught with issues. I'll do some reading about this but for now it will be removed from the charging circuit.

Q: Is there a problem with running a new FAT cable from the Alternator NEG(-) to the starter NEG(-) where there's a very large cable indeed going back to the start battery NEG(-)? The two battery bank NEG(-) terminals are wired together with a substantial battery cable, as big as the one to the starter. Or do I need a dedicated NEG(-) cable from the alternator back to the ground bus bar?

Q: I'm sure I can get an accurate reading of my charge voltage by putting a large load on the house bank with the alternator running and the engine revved up. I have a DC vacuum cleaner that draws about 12A, that ought to be enough to put it in bulk charge mode. However, with no ammeter in series, is there any (reasonably cheap) way to tell how much current I'm pushing into the batteries? Is it as simple as measuring voltage drop between the alternator and battery, measuring the resistance of the wire, and computing amps using Ohm's law?

Q: Maine Sail guessed I may have blown diodes... Would I need to remove the alternator and take it to a shop to test this? I have an oscilloscope which could probably be used to see the DC pulses... if they're evenly spaced I'd surmise all 3 diodes are working, if there are gaps in the pattern there's a dud. However, looking at the length of my O-scope probe, I am having trouble seeing me lying on my side next to the running engine in the port cockpit locker reading and adjusting the oscilloscope... Are these diodes accessible from the outside of the case, and are they user replaceable, or are they buried in the windings? I have extensive experience with electronic repair, another hobby of mine is restoring vintage audio equipment so it's as simple as opening the case and replacing them I'd prefer to do it myself to save some money. Any idea of cost of replacing diodes at a shop? If it's >$200 I suppose I'd be better off with a new bigger better alternator.

Q: If it were you, would you put money towards a) new alternator b) external regulator c) battery monitor. If I can get my 51A out of the alternator, or even 40 amps, I can live with the 2-1/2 hours per day of charging. I cannot live with the current situation of ~7 hours charging at 15A.

In my reading, it appears that the best way to wire things is to have the battery switch act as a "use" switch for ALL loads including starter. I've described my BlueSea switch, and I think I can wire one end of each switch together to get to where I want to be. My only concern is whether the toggle switch (marked "house") can handle the current of a (future) 100A alternator and the load associating with starting the engine (multiple hundreds of amps for short duration?). Or even 40A sustained. My gut says no way given the insignificant action of the switch. My other option is to wire the house bank through the "engine" switch on the panel, use only the house bank (including for starting) and hope the toggle switch plus ACR (60A max continuous) can get me started in a pinch. The heavy-duty parts of the switch panel are clearly designed to have the house battery assist with starting and nothing else.

Again, thanks so much for all of the help... it is very much appreciated and has already saved me money as I was ready to go ahead and buy a new alternator and regulator when there are so many other issues that need to be dealt with first in order to determine if I even NEED a new alternator.

I live 250 miles inland from where the boat is kept, so I'm trying to have a plan of attack before I go down to do maintenance as shops like alternator shops and machine shops and auto electric places tend to be closed on weekends.

Oh, one last question: do you guys make your own cables? If not who makes them? Auto electric places? Motor shops? What tools are required?

Dave
CS36T
 
#13 ·
I believe I need to go to copper wire size AWG 3 to get below 3% loss using 10 ft length, 100A, 14.4VDC. Can't see my little 30hp Westerbeke with 1/2" belt driving much more than that without a serpentine conversion, but I'd need AWG 2 for 125A to remain below 3% loss.
 
#14 ·
Genuine dealz online can make up the cables to your measurements. Including crimps, they use a heavy duty crimper and do a lot of them so you know it is done right. I would suggest going to the cable you would use for the 100 amp alternator figuring you will likly go there some day anyway. Then it is done.

Sent from my XT1080 using Tapatalk
 
#15 ·
IIRC you don't need an oscilloscope to see if there's AC coming out of your alternator. Just use a cheap DMM in either the AC voltage mode, or the resistance mode. Disconnect the batteries, check the resistance from the alternator's charging stud to ground. You should see zero one way, infinite the other way. If you don't see a zero--that's a shorted diode creating the value.

Even simpler, take the AC voltmeter and see if the alternator puts out ANY AC voltage while running. Now reverse the leads and check again, because the way some DMMs are built, they will get a "false AC" reading on a DC voltage, when the leads are "backwards". And that's just normal. But if it shows some AC value like 14vac in either position? That's a blown (shorted) diode.

Diodes can fail open or fail shorted, either way you lose.

Something nobody mentions is that when you have a thoroughly used boat, which probably does not have the original alternator, you need to check the alternator PULLEY SIZE and alternator specs. The power that an alternator puts out depends on the rpm of the alternator. Stick on the wrong pulley for that alternator (even if it was the original one for the boat) and it will spin at the wrong speed, and that can cut your output in half.

I'm only sensitive to that because we upgraded a dead replacement "Damn, where'd y'all get that from?" alternator to a new one, and coincidentally found out that we'd have to have a new pulley fabbed up at a machine ship. And by having it fabbed up correctly, we cut the charging time IN HALF.

You need to check on the alternator's minimum rpm (below which you get next to no amps) and maximum continuous rpm (above which, it burns out) as well as the point where it gets full rated output, i.e. 50A.

Then you chose a pulley that works with your cruising rpm, to get as close as you can to maximum power, while your idle speed and "battle" speed" won't totally insult the alternator if you use that pulley size. Some compromise may be in order, every alternator is somewhat different.
 
#16 ·
Hmm. Pulley size. Will check, good idea. I know the alternator is putting out SOME voltage as I'm reading it on my ammeter and voltermeter and my batteries do eventually charge when I motor for long periods. It's a matter of how much. I figured out from the manufacturer's website that the diode trio is an assembly which is in fact replaceable, and I found one for about $12 on eBay. I am going to use your diode check method Alternator POS --> ground and see what I see.

Just having a Eureka! moment here. From memory the pulley on the alternator is about the same size as the pulley on the engine, maybe a little bigger but no more than 1.5X. That'd mean that I'm only spinning the shaft ~2000rpm +/- and the alternator curve shows I don't hit 50A until about 5000rpm. I should be getting 30A out of it at 2000, but considering long runs of undersized wire, the crappy splices, the ancient ammeter in series, and the fact that the output is not connected to the house bank... well maybe nothing wrong with the alternator at all, it's just the wrong alternator for this application.

If the engine has, let's say, a 3" drive pulley, in order for me to hit max output at 10000rpm's while cruising at 2000rpm's I'd need a 5:1 ratio so a 15" pulley on the alternator! Even to hit 5000rpm's I'd need a 7.5" pulley. Much to consider (and measure!) as my alternator is pretty darn close to the sidewall of the engine compartment as it is.
 
#17 ·
where did you get those upside down numbers? you have the thinking a bit backwards. most alternators are max output at around 5500 and most older model engines are at cruise rpm of 2750. so this means that the alternator is running about twice the speed of the engine. the alternator pulley is about 2.5" diameter so the motor pulley would be around 5" diameter. Engine pulley, big and alternator pulley, small. every time the engine turns one turn the alternator turns two turns. your boat may vary some.
 
#20 ·
Ohms law probably will not work for current measurement from one end of the wire to the other. Reasoning: to truly measure the current through it you need to know the voltage drop across the wire, which in theory and in practice is almost zero. In addition the resistance is almost zero. In theory you could do it of course though you would need highly accurate measurements of the the voltage difference and the resistance also.

A better way and easier is to use a clamp on ammeter and measure the current flowing through the wire in question through induction.

You also mentioned you had splices I would get rid of all of them, with 20 years of troubleshooting electronics I have learned that splices that have been in a system for a long time are a good place to start looking for the fault. Splices have there place as a temporary fix, and should be replaced with a permanent solution at the earliest possible time. Also remember as you rewire to label both ends of the wires, yes even the ones to the battery makes things easier and you do not have to think or trace wires manually, not a fun task.

Thomas
BSEE/BSCE
 
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