Ask PYS - How Can I Tell if My Alternator Is Working?

Frank asks, "I watched your video about fusing the alternator and you recommended always carrying a spare alternator on board. How do you tell when your alternator has blown?"
Read our Tech Talk Article from Pacific Yachting Magazine, "Charging Batteries from an Alternator", www.pysystems....
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[@patdghop]

Hey Jeff I noticed that my voltage didn’t show a change on my Yanmar diesel until it ran and reached 135 degree temp. After reaching this temp it would start to show a charge. Pulled the alternator and had it checked at a local shop and everything tested perfect. After further Investigation it turned out that the engine has an air intake heater that turns on until the engine reaches temp. I installed a Victron battery monitor to prove that there was positive charge. best addition to my boat yet. Thanks for the great advice in these videos.👍👍

[@PacificYachtSystems]

Thanks for sharing patdghop! Interesting how a large a load can mask the alternator output. That's why it's so hard to know if your alternator is working just based on voltage.

[@SailingCatamaranElement]

Jeff, great answer to this question, but I also suggest you mention the case of an alternator malfunctioning by overcharging and what an owner should do if they detect this situation. I apologize in advance, but my personal question is a bit complex: Our Langley BC family are bluewater sailors and I attended advanced marine electrical and diesel training from the Annapolis School of Seamanship before purchasing our sailboat in Turkey. We have sailed the past 6 years from the Eastern Med to SE Asia and we are currently awaiting international borders to re-open and an effective vaccine to continue our travels. We own a french performance catamaran (Catana 471) with twin Volvo D2-55a diesels, with each diesel having dual "standard" 60A alternators utilizing twin battery isolators and 2 starting batteries. We currently have a 900Ah Sonnenschein gel house bank with 1300W of solar and a hydro charger which serve us very well without the need to upgrade the alternators, but I feel when we do run a single engine (typically for fuel conservation) or both to arrive at an anchorage before sunset (or while passing through the Panama Canal), I don't feel the existing configuration is charging/protecting our batteries as efficiently as possible, considering the number of alternators concurrently running. I am looking to upgrade the system to a staged regulated charging technology with some type of read-out (LEDs etc.) that is compatible with the thought of upgrading the house bank to Lithium in the near future. I was wondering if you have any suggestions of a good product(s) which would be ideal for our situation.

[@PacificYachtSystems]

Based on your boat size, I'd consider getting higher output alternators, at least 90 amps with single v-belt, or 200 - 250 amp range with serpentine belt. In turn, you'll drive those alternators with a external regulator like the balmar 614. Assuming you have a standard internal regulator on your alternator, you should never see a voltage higher then 14.4 volts outputting from your alternator.

[@littlehouseinthecove3570]

Good job Jeff👍

[@chachi5975]

You have mentioned in the past that switching off your battery while the engine is running will ruin the alternator. I'm considering putting in a Lithium battery as a starter, (the company says it has 900CCA so it's powerful enough to be used as a starter battery). My question is what if the BMS shuts down the battery for some reason, low voltage, low temperature, high temperature etc. Would that be a potential danger for the alternator? Thanks for all these QandA videos 😊

[@PacificYachtSystems]

Great point and yes. If your BMS has only one positive post to control and not two (one post for loads and another post for charging) then yes it's possible you'll damage the alternator when your BMS shuts down the only battery post.

[@compassioncampaigner728]

Hi Jeff. Im a Jeff too. Hoping you have a thought or 2 on my, IMOpinion, altetnator issue: 2 inboards Both start nicely 20 mins run time or so and the port motor dies Using emergency start, the port engine will turn over nicely- even start for a moment- then shuts down as soon as the emergency start is released Immediately after engine shut down, charger shows putting 40 plus amps out to charge up the system. In my way way layman thought, I am thinking the alternator is not putting out-- the shol¹1😮re power is topping the battery off- port engine starts beautifully- run 25 mins or so and then dies. Port engine battery not gettng any charge from the alternator and is just using up whatever it has stored to run the motor for 25 min ? I am just wsnting to know if my alternator is putting out juice to the battery at all? Appreciate your thoughts. Big block Mercruiser 1997 Sea Ray aft cabin. Alternator is not old at all, BUT it is FL and all mechanical gear takes a beating.

[@nathanbajada1300]

The tiny 60amp alternators on my 3208T cats don't charge a idle speed (650rpm). I spend up too 10hrs a day slow trolling live bait and with my high electronic loads, fridges, chart plotters, stereo, sonar etc my battery voltage and charge drops quite quickly! What can you suggest to help improve or overcome this problem without me needing to run my generator and onboard 240v battery charger? Thanks!

[@PacificYachtSystems]

That's a tough one, have you consider changing your stock alternators for an alternator that outputs at idle, Balmar is a good starting point to consider.

[@torstenhansen4308]

Is there a reason that we can’t just measure the amperage flowing to the battery? For example this set-up: 200 Amp alternator externally regulated to provide a 150 Amp charge to a 300 Amp hour lithium house bank. 0.5C is the recommended charge rate for the batteries and they will absorb it until full.

[@PacificYachtSystems]

Good point Torsten and yes doable. But most boats won't have an amp gauge on the battery.

[@torstenhansen4308]

@@PacificYachtSystems Can you recommended a quality multimeter with amp reading ability for AC and DC? I need to get one.

[@RustyBaban]

i just took my alter off for a bench test ... i will try this next next time ...this clip would have save me some time ... and will consider getting a spare ... thx you for all your advice ... Moody 376

[@PacificYachtSystems]

Thanks Rusty for sharing.

[@nonobebert7646]

Does the voltage increase even if the battery is fully charged ?

[@PacificYachtSystems]

Yep, the battery does rise until 14.4 volts. Depending on the size of your battery bank, the alternator size, and how empty the battery is, determines the length of time it will take to get 14.4 VDC.

[@nonobebert7646]

@@PacificYachtSystems Thanks. Does the battery stay at 14,4 V as long as the alternator is turning ?

[@samaeri]

You can look at your tachometer as well

[@PacificYachtSystems]

Good point, as many tachs are feed from the alternator.

[@alcibiadesmarcialneto922]

Put a shunt and check the current is a good way if the alternator is working properly.

[@PacificYachtSystems]

Good suggestion and make sure the alternator connection is keep as short as possible. In the past boat builders ran the alternator current to amp gauges at the helms, but by doing so, created really long alternator cable runs and that caused excessive voltage drop.

[@javierbetancourt9388]

💯

[@PacificYachtSystems]

Thanks!

[@robertschulke1596]

Understanding your batteries and regulator is also very important. Check out batteryuniversity.com. Learn about bulk, absorption, float, Peukert exponent, and C rates. The time to solve charging problems is before you go out.

[@PacificYachtSystems]

Thanks for sharing Robert.

[@svamour4574]

I appreciate your show but it is exhausting. Why not design a solar array and lithium battery and alternator and everything in between that works on a boat. One offs are expensive. Will someone design a system with everything that works together so the customer will not have to pay a thousand percent markup?

[@PacificYachtSystems]

Good question.

[@scruff7559]

There's no economy in not installing a Battery Monitor.

[@PacificYachtSystems]

Well said!!! Favourite line of the week!