What's your Voltmeter Read?

[TBOT422]

What's your voltmeter read at the helm when the engine is running?

I'm still trying to diagnose what I thought was an alternator problem on our last cruise. After running the house battery down to about 75 per cent (about 12.3 V), my helm voltmeter was showing less than 13 V with the engine running. I thought that any time the engine was running, you should see 13.5 V to 14.5 V coming out of the alternator. At least that's what the manual says. What I was seeing during our cruise (and current testing) is that if the battery was drained down, the voltmeter (both helm and battery monitor) basically showed about 1/4 to 1/2 V more than whatever the battery voltage was before I started the engine, then slowly went up as the batteries gained charge. Slowly, is the operative word. From my battery monitor, I was showing an initial charge rate of 40-45 amps right after starting the engine. This quickly dropped off to about 25-30 amps within 10-15 minutes. That meant that my 50-amp alternator basically was only putting out about half that much. I thought the alternator was going bad. Today, I took it to a shop and had it tested. The tech said it was working fine. That was the way it was supposed to work. It's not going to show 13.5 V if the batteries are discharged and won't show that until they get recharged. At 25-30 amps, that would take nearly 10 hours of motoring. Maybe I never noticed before I installed the battery monitor, but I don't recall the helm voltmeter ever showing anything below 13.5 V with the engine running since we owned the boat. I'm wrestling with having lost my mind about how I thought it was supposed to work and trying to find another source for the problem (if there even is a problem). Maybe the belt is slipping under load, or maybe one of the batteries is not up to snuff, or maybe there is something else I am missing. Any ideas?

[wolfe10]

Only way to get an alternator to put out what you would like is basically the same as has been done with battery chargers. SMART REGULATORS start your alternator in bulk, then absorption, then float mode. They are not inexpensive, but a good investment, particularly if you are running your engine just to charge the batteries.

Here is the regulator we use: Xantrex XAR Digital Alternator Regulator. PN 84-2006-01

http://www.xantrex.com/power-products/p ... lator.aspx

[TBOT422]

Thanks Brett,

Given the data I have been gathering from the new battery monitor I installed last year, I was beginning to think the problem was with the charging profile in the internal regulator in the alternator. We don't necessarily use the engine just to charge up the batteries, as we also have a portable Honda that we can use to fire up the shore charger. In a couple of days at anchor, we consume about 200-250 Ah. I was expecting that the 50-amp alternator would replace at least a majority of that in 4-5 hours cruising to the next location, when in fact it doesn't. It is no more effective at replacement the consumed Ah than the 30-amp shore charger. What surprised me was that after the batteries were run down to 12.5 V or so, the helm voltmeter never got above 13 V for an entire day of motoring. I wasn't expecting that.

$250 for a smart external regulator may not be a bad choice given our cruising style. It certainly seems better than spending that or more on a 75-amp or 100-amp 'dumb' alternator that still has an ineffective charging profile to re-charge a 600 Ah battery bank. What are the downsides or drawbacks? Or should I just bite the bullet and install solar panels to come closer to meeting our electrical consumption needs?

Thanks

[BillBerner]

Have you tried reading the voltage directly off the tap to see what it's really outputting?
Voltage drop, corrosion, etc being what it is. Definitely where I'd start.

[wolfe10]

Gary,

While many would not agree with me, our choice for long term cruising is a 120 amp alternator with smart regulator.

We are able to keep batteries up (discharge to about 50 percent, then recharge to 85 percent) with 30 minutes run time AM and PM-- when we want to have hot water as well.

Then, once a week, if possible, use shore power overnight to restore batteries to 100 percent. Has worked on several trips from Texas to the Bahamas for the winter.

And, one of the beauties of a smart regulator is that you can put the sense wire on the battery terminal. If your particular battery chemistry wants, say 14.2 VDC in bulk mode, you can make sure that is the voltage at the battery-- with the alternator putting out a couple of ten's more to compensate for line loss.

[KenKrawford]

Gary I have no direct experience but a friend of mine installed a Sterling Alternator Regulator on his Catalina 42 and has been very happy with it.

http://www.sterling-power-usa.com/ProRe ... lator.aspx

[Aussie Mate]

Testing replies, do not respond please.

[jking]

It sounds like things are working perfectly, the charge rate will reduce once the batteries are at the alternator voltage maximum set point. I think you are not used to seeing what has been happening in your electrical system before. The maximum charge rate for most batteries is 1/10th of the Ah capacity, which is around 20 Amps for each 4D battery, so if BOTH is selected on the battery selector 40 Amps is the max charge rate, reducing as the battery voltage gets higher. It is not wise to increase the size of the Alternator as its pretty well matched to the battery capacity of the boat. Bigger is not better in this case unless you have a larger than normal battery bank for the C350. Your charging rate is limited by the batteries ability to accept the charge, not your alternators output in the case of the lead acid batteries.


Jan (I am an electrical engineer who works in the battery charging industry with solar energy)
#303

[TBOT422]

Jan,

Thanks for the reply. I think you are correct, things are working as designed, just not working in the manner I would like. You're also correct about my not being used to seeing how the electrical system was working before I installed the battery monitor. It has given me more insight as to what is happening.

I am confused by the following:

the charge rate will reduce once the batteries are at the alternator voltage maximum set point

That does not seem to be the case. The data on my battery monitor shows a charging rate of about 45 amps immediately after starting the engine. It drops off to about 30 amps in 2-3 minutes. Obviously the battery voltage of a well discharged battery bank is no where near any maximum set point by that time.

We now have 3 pairs of 6V golf cart batteries with about 600 Ah of capacity. When discharged to 70 - 80 per cent they clearly have the ability to accept more charging current than the stock alternator is putting out. I suspect there is no way to adjust the alternator's output based on the fact that we now have a larger battery bank other than replacing it with a larger one and adding external smart regulation.

[wolfe10]

Gary,

A smart regulator will allow you to "get what you want" from your alternator, just as a smart charger or smart inverter/charger will.

It will start in bulk mode (higher voltage which equates to more amps being fed into the battery), then absorption, then charge rate lowers to float.

And, if you put the sense wire for the smart regulator on the battery itself, your battery will get absolutely the highest safe charge rate, since all line/connection loss is compensated for.

[TBOT422]

Brett,

That is clearly an option. I am weighing the pros and cons of a solution.

1. External regulator with existing alternator. Would increase output from around 30 amps to around 50, and only cost $300. Not a lot of money, but doesn't really get me where I want to go, and the alternator is likely to not last as long.
2. 80-120 amp alternator with external regulator. Probably gets me where I want to go for $1000-$1500. Downside is I have to run the engine and it will take about 3-4 Hp off the engine.
3. About 300 watts or more of solar panels for $2000 - $2500 by the time everything is done.
4. Replace the 30-amp shore charger with something on the order of 75-100 amps and run it from the Honda 2000. I haven't even looked at the cost to do this as it requires running the generator a couple of hours each day.

Or I could really address the real issue: Completely rebuild the refrigerator and replace it with something more efficient. I've done a lot of the things that are easy to do, but it still seems to run nearly 90 per cent of the time. My guess is I would likely spend more than the cost of solar to do this job right, and it still wouldn't completely solve the issue, it would just make it better.

I'm leaning toward the solar solution. Then the existing alternator should not have so much work to do replacing ALL of a couple of days running the refrigerator.

[wolfe10]

Gary,

Weighing heavily on our decision was the fact that we wanted hot water twice a day. Engine run time to make hot water AND charge the batteries dictated our choice.