Anonymous
01-22-2003, 10:34 PM
Bill Thomas
normal member in standard member. 1. Battery Charging
I do not think my alternator is putting out the amps it should. I am seeing 13 Volts on the volt meter, but the batteries are getting run down even with many hours of running at 1200 rpm plus most of the day.
What is the easiest way to test the output of the alternator?
I am getting enough voltage drop when I start the engine to reset my fish finder.
My engine always seems to turn over very slow, is this normal? It always starts quickly.
Date: 03:58 p.m. on 04-17-2001
Leprechaun
premium member in standard member. 2. Re:Battery Charging
Bill - either you have a weak alternator or your batteries are losing their ability to retain a charge or both. Forget the ridiculously inaccurate dash mounted volt meter and put a hand-held Digital Volt Meter (DVM) across your starting battery. Now crank her up. Did the voltage fall below 10.5V? I'll bet yes, since your Fishfinder is resetting itself. Most of them will work down to about 11V after that they will shut down. (Incidentally - this used to happen to me when I first got my boat and initially wasn't aware that the alternator wasn't putting out more than 20 amps at 3000rpm. - Insufficient to keep the batteries topped up).
After your engine finally starts, what's the digital Volt meter say? Should jump up to between 13.9 - 14.2V. Give it some gas and get her over 1500 rpm for this test as some marine alternators (1 wire hot-lead types) will not energize the voltage regulator till around 1500 rpm. If you don't see the voltage come back quickly to at least 13.9V you probably have a weak alternator.
At this point, proper further testing will require a fairly expensive load testing instrument known in the trade as an AVR. this will hook to your battery(s) and when the internal carbon pile is energized it will induce a parasitic load on your battery of approx 75% of the rated load (CCA) of the battery. If the voltage falls below 9.5V then its is recommended that the battery(s) be removed, charged with an external charger and retested. If they fail again, replace them.
The same AVR instrument will also be used to test the alternator. An inductive lead will be clipped over the red field wire going from the alternator to the battery(s) and a load equal to 90% of the alternator's rated output will be placed on the batteries with the AVR's internal carbon pile, but this time with the engine running at 2500rpm. If the voltage falls below say 10V then safe to assume that the alternator is in need of rebuilding/replacement.
These AVRs are pretty expensive (good ones run in excess of $1K, most are around $2500) so many home owners (And some cheap-ass repair shops) try to simulate these tests with the little bootleg silver "Toasters" that are sold in discount auto parts houses. N/G - those units only load to around 100A so they give false positives on testing. Then you go out and lose your power on the next trip. A nice slow tow back to your dock results, naturally.
IMO If you want to spare yourself grief, get a freshly rebuilt alternator in there and then take out you batteries and give them a good charge with a powerful charger, like the one you corner garage would use to jump start a car. I bet the alternator is bad and the batteries are marginal, due to the alternator not maintaining them for the past while.
There you go, that's pretty much the sum total of "Charging System Problems 101" as related by a retired and very tired ex-Snap-on Tools dealer, who sold more than his share of AVRs in his day.
That'll be $149.50 please. Ooops, sorry, old habits die hard. ;-}
Rgds,
Leprechaun
Date: 11:26 p.m. on 04-17-2001
capt_D
normal member in standard member. 3. Re:Battery Charging
Leprechaun, when replaceing a alternator how many amps would you reccomend for the average equiped boat? I was guessing around 70 amps. Also there are different size pulleys available and i would think since we turn low rpm's we would benefit from a pulley ( small ) that would spin the alternator faster. ( Especially when trolling all day. )
capt_D
Date: 01:13 p.m. on 04-18-2001
Leprechaun
premium member in standard member. 4. Re:Battery Charging
Capt. D - my rig originally came with a 35A alternator - which wasn't even putting out 20A by the time I took ownership. I upgraded to a 70A model, which was available in a marine model over the counter from my local auto parts shop. I think on an "Average"-equipped boat that should be fine.
On my boat however, I burn 1 alternator up each season, and here's why: On my boat I have the following up and running almost constantly a Raytheon RL9 radar, a SiTex 10" CRT fishfinder, a Cetrek autopilot, a second smaller Hummingbird fishfinder, plus intermittant use of lights, and worst of all a big honkin' Good windlass, with the H/D motor. Hit the switch and watch your batteries drain. In the winter you can add the constant load of the fan in my cabin heater.
The problem is exacebated on my rig because at anchor, with the engine off, I still run the Sitex because with the wreck fishing and drifting I do, its obviously critical to remain over productive rubble bottom. That Sitex is like running a small Television off your accessory battery, thus when I fire up the engine after a day at anchor, it immediately kicks the voltage regulator full on, thus the alternator is running full blast for the entire trip home. You can clearly hear it singing.
Plus, in the Fall I do plenty of low-rpm Bass trolling, many times as low as 475 rpm. No need to tell you that the alternator fields just don't energize at that speed. So again, a big strain on the alt when I power up to go home.
Adding to the electrical woes is the fact that Shamrock came up with the truely ingenious idea of the battery bridge over the engine, but it can only hold the smallest of Marine batteries - the Group 24 size. This size is marginal for the type use I give them.
The solution of decreasing the size of the alt pulley would be a good one under normal circumstances, but at an engine rpm of around 2950 - my cruise, I'm leery of small pullies, I think they might over-speed the alt.
So the choice I have to make each season is to put up with a marginally effective alternator for around $65 plus the core or upgrade to a super-duper custom-made 125A model with a separate 3-stage voltage regulator - this costing around $600 to do it right. Plus my labor. So far, I've resisted the urge to upgrade, but you can see that it really doesn't make sense to stay with the small unit, except I always put money into other upgrades and tackle purchases, never enough for a "Luxury" upgrade like an alternator. So maybe this year I go for the bigger alt. I don't what else might break and require immediate triage, so I'm keeping my fingers crossed.
Rgds, Leprechaun
Date: 05:19 p.m. on 04-18-2001
Engineman
normal member in standard member. 5. Re:Battery Charging
Hey guys don't forget to check the belt for tightness. Should flex about 1/2" when tight. Sometimes you can't tell the belt is slipping by a meeter. But all the other stuff is good advice after the belt.
Date: 10:14 p.m. on 04-18-2001
normal member in standard member. 1. Battery Charging
I do not think my alternator is putting out the amps it should. I am seeing 13 Volts on the volt meter, but the batteries are getting run down even with many hours of running at 1200 rpm plus most of the day.
What is the easiest way to test the output of the alternator?
I am getting enough voltage drop when I start the engine to reset my fish finder.
My engine always seems to turn over very slow, is this normal? It always starts quickly.
Date: 03:58 p.m. on 04-17-2001
Leprechaun
premium member in standard member. 2. Re:Battery Charging
Bill - either you have a weak alternator or your batteries are losing their ability to retain a charge or both. Forget the ridiculously inaccurate dash mounted volt meter and put a hand-held Digital Volt Meter (DVM) across your starting battery. Now crank her up. Did the voltage fall below 10.5V? I'll bet yes, since your Fishfinder is resetting itself. Most of them will work down to about 11V after that they will shut down. (Incidentally - this used to happen to me when I first got my boat and initially wasn't aware that the alternator wasn't putting out more than 20 amps at 3000rpm. - Insufficient to keep the batteries topped up).
After your engine finally starts, what's the digital Volt meter say? Should jump up to between 13.9 - 14.2V. Give it some gas and get her over 1500 rpm for this test as some marine alternators (1 wire hot-lead types) will not energize the voltage regulator till around 1500 rpm. If you don't see the voltage come back quickly to at least 13.9V you probably have a weak alternator.
At this point, proper further testing will require a fairly expensive load testing instrument known in the trade as an AVR. this will hook to your battery(s) and when the internal carbon pile is energized it will induce a parasitic load on your battery of approx 75% of the rated load (CCA) of the battery. If the voltage falls below 9.5V then its is recommended that the battery(s) be removed, charged with an external charger and retested. If they fail again, replace them.
The same AVR instrument will also be used to test the alternator. An inductive lead will be clipped over the red field wire going from the alternator to the battery(s) and a load equal to 90% of the alternator's rated output will be placed on the batteries with the AVR's internal carbon pile, but this time with the engine running at 2500rpm. If the voltage falls below say 10V then safe to assume that the alternator is in need of rebuilding/replacement.
These AVRs are pretty expensive (good ones run in excess of $1K, most are around $2500) so many home owners (And some cheap-ass repair shops) try to simulate these tests with the little bootleg silver "Toasters" that are sold in discount auto parts houses. N/G - those units only load to around 100A so they give false positives on testing. Then you go out and lose your power on the next trip. A nice slow tow back to your dock results, naturally.
IMO If you want to spare yourself grief, get a freshly rebuilt alternator in there and then take out you batteries and give them a good charge with a powerful charger, like the one you corner garage would use to jump start a car. I bet the alternator is bad and the batteries are marginal, due to the alternator not maintaining them for the past while.
There you go, that's pretty much the sum total of "Charging System Problems 101" as related by a retired and very tired ex-Snap-on Tools dealer, who sold more than his share of AVRs in his day.
That'll be $149.50 please. Ooops, sorry, old habits die hard. ;-}
Rgds,
Leprechaun
Date: 11:26 p.m. on 04-17-2001
capt_D
normal member in standard member. 3. Re:Battery Charging
Leprechaun, when replaceing a alternator how many amps would you reccomend for the average equiped boat? I was guessing around 70 amps. Also there are different size pulleys available and i would think since we turn low rpm's we would benefit from a pulley ( small ) that would spin the alternator faster. ( Especially when trolling all day. )
capt_D
Date: 01:13 p.m. on 04-18-2001
Leprechaun
premium member in standard member. 4. Re:Battery Charging
Capt. D - my rig originally came with a 35A alternator - which wasn't even putting out 20A by the time I took ownership. I upgraded to a 70A model, which was available in a marine model over the counter from my local auto parts shop. I think on an "Average"-equipped boat that should be fine.
On my boat however, I burn 1 alternator up each season, and here's why: On my boat I have the following up and running almost constantly a Raytheon RL9 radar, a SiTex 10" CRT fishfinder, a Cetrek autopilot, a second smaller Hummingbird fishfinder, plus intermittant use of lights, and worst of all a big honkin' Good windlass, with the H/D motor. Hit the switch and watch your batteries drain. In the winter you can add the constant load of the fan in my cabin heater.
The problem is exacebated on my rig because at anchor, with the engine off, I still run the Sitex because with the wreck fishing and drifting I do, its obviously critical to remain over productive rubble bottom. That Sitex is like running a small Television off your accessory battery, thus when I fire up the engine after a day at anchor, it immediately kicks the voltage regulator full on, thus the alternator is running full blast for the entire trip home. You can clearly hear it singing.
Plus, in the Fall I do plenty of low-rpm Bass trolling, many times as low as 475 rpm. No need to tell you that the alternator fields just don't energize at that speed. So again, a big strain on the alt when I power up to go home.
Adding to the electrical woes is the fact that Shamrock came up with the truely ingenious idea of the battery bridge over the engine, but it can only hold the smallest of Marine batteries - the Group 24 size. This size is marginal for the type use I give them.
The solution of decreasing the size of the alt pulley would be a good one under normal circumstances, but at an engine rpm of around 2950 - my cruise, I'm leery of small pullies, I think they might over-speed the alt.
So the choice I have to make each season is to put up with a marginally effective alternator for around $65 plus the core or upgrade to a super-duper custom-made 125A model with a separate 3-stage voltage regulator - this costing around $600 to do it right. Plus my labor. So far, I've resisted the urge to upgrade, but you can see that it really doesn't make sense to stay with the small unit, except I always put money into other upgrades and tackle purchases, never enough for a "Luxury" upgrade like an alternator. So maybe this year I go for the bigger alt. I don't what else might break and require immediate triage, so I'm keeping my fingers crossed.
Rgds, Leprechaun
Date: 05:19 p.m. on 04-18-2001
Engineman
normal member in standard member. 5. Re:Battery Charging
Hey guys don't forget to check the belt for tightness. Should flex about 1/2" when tight. Sometimes you can't tell the belt is slipping by a meeter. But all the other stuff is good advice after the belt.
Date: 10:14 p.m. on 04-18-2001