Engine battery charging

Bill Roosa · Jul 6, 2011

Check the installation of the isolator. Mine has two different diodes with different voltage drops across them. Assuming your alternator voltage sense wire is attached to your house batteries AFTER the isolator you should attach the diode with the greater voltage drop (lower voltage during a charging session not with the engine off) to the starter battery. This gives the house a preferential charge. I've had no problems motoring with setup.
If you wire it the other way round the start bat gets preferred. I'd also take out the CB as it is not needed and just another source of potential problems.

Graycruiser · Jul 11, 2011

I agree with Bill and recommend you consider a direct positive wire from the alternator to the house bank with no switching. This protects the alternator diodes from the chance of an open switch. I also recommend the BlueSea dual circuit switch. It switches both the starting bank and house bank separately at the same time between two positions: On or Off. Nothing to think about.

What's the chance you might have blown the diodes?

mitiempo · Jul 16, 2011

I would recommend against the Blue Seas Dual Circuit Plus switch. It doesn't give you the option of using the house bank for engine starting, only combine. If the engine battery is too low to start the engine there is absolutely no reason to parallel the banks. This has the possibility of leaving you with 2 banks that are unable to start the engine, depending on house bank size, soc, and battery technology, agm being the worst case.

Stick with a 1,2,both switch with the charge current going direct to the house bank. Charge the start battery with an Echo Charge, Duo Charge, or ACR. This will give you the most flexibility for charging and engine starting.

Stu Jackson · Jul 17, 2011

Any switch that ONLY allows you to parallel a bad bank with a good one has some inherent conceptual drawbacks. Use a 1-2-B switch.

Bottom of page one and then read on: http://forums.catalina.sailboatowners.com/showthread.php?t=104505

Bill Roosa · Jul 18, 2011

Getting back to the question, RE house battery not getting much charge. Given that the alternator is in fact OK you should see a voltage increase on the house bank when you start the engine. The regulator (you didn't say if you had external or internal but 150 amp alternator surely has some kind of 3 stage regulation I'm thinking) will take the batts to 14.4ish volts and then after some predetermined time test them by turning off the alternator momentarily to get the (yes I know but that is the only thing I can think to call it without getting reallllly geeky) resting voltage. It then proceeds to the correct "program voltage" from there. Either bulk charge, absorption or float. Some do it on a timed program also once bulk is accomplished.
SO WHAT you ask? Well the control in all this is the battery. If your batts are charged up it does not matter if you have a 1000 amp alternator, the batts are going to show charged and the regulator is going to dutifully not try and fry them. Since all lead acid batteries suffer from the limitation of max charge rate of 25% (some more some less) of the AH capacity of the battery I'm sure that your 150 amp alternator will not be fully engaged unless it is both connected to a 600 AH bank or greater and the bank is discharged below 50%. At all other times you are going to get less than 150 amps due to the nature of lead acid batteries and the size of your bank.
This is why I don't think getting a huge alternator is of much use unless you intend to drive an inverter while running the engine or operate a winch/windless while you motor. It can work great to have an engine drive an alternator that drives an inverter that runs your 120 volt water heater but there are better and more energy efficient ways of doing most things than that method. It is handy for the occasional 1000 watt hair dryer session though as that is a real bank breaker. Proper training can result in significant energy savings and proper choice of first mate is key. Your mileage certainly will vary.

How big is your battery bank?
What is the state of charge (SOC) of the bank when you noticed the lack of charge?
Did you have anything electrically "big" running when you noticed the lack of charge?

mitiempo · Jul 18, 2011

I would also recommend a good battery monitor such as the Victron BMV-600 to monitor your house bank as a voltmeter will tell you whether they are charging (around 13.2 or so) in float or bulk (14.4 or so) but not much else.

Maine Sail · Jul 18, 2011

capta said:
The Perkins 4-236 on my Pearson has a 125 amp alternator on the engine which runs to an isolator which separates the engine & house batteries. I added a 150 amp BluSea circuit breaker/switch to the engine battery side of the isolator (after it) so I could get the majority of the charge to the house batteries (600+ ah of 4 Trojin T-145's) w/o overcharging the engine battery when powering.
Problem is; the house bank does not get much (if any) charge, even if the circuit breaker is on & the engine battery is charging. I have a voltage meter on the pedestal to monitor the house bank.
Any thoughts?

Capta,

Do you have an ammeter or battery monitor so you can see current going into or out of your bank or are you simply relying on voltage to determine how much "charge" you're getting?

There is really no need to switch off the start battery as it will never be taking more than an amp or two from just starting the engine and will not hinder the performance of the alt by much if any under normal operating situations.

My guess is that your banks are nearer to full than you think they are thus low output from the alt. Contrary to perceptions about alternators it is the battery bank that determines the output of the alternator, not the alternator. The banks could also be very low and the alt has not been able to bring the bank up to absorption voltage. This does not happen instantaneously and bulk can take a while especially with a large bank like you have.

A volt meter really tells you very little about your charging system other than the alternator is putting out more than the resting voltage of the banks. For example if the banks are near full and you have a three stage external regulator you could be in float mode which would be somewhere between 13.2v and 13.6v...

Another possible problem is that your alternator may not be sensing the battery bank voltage, at the battery positive terminal, which is VERY critical with diode based isolators. These isolators can have voltage drops of anywhere between 0.7v and 1.2v depending on the product and how many amps you are trying to pass through it..

The Pearson 530 is a fairly complex system when stock but most owners have tweaked them beyond stock by this point in time. Also the long runs to the banks, you probably have one under the aft cabin berth, and one in the engine room, can make for some serious voltage drop if your connections are not clean and good.

Do you have the standard 1/2/BOTH/OFF switch at the bottom of the companionway to the starboard side or has it been further modified?

Stu Jackson · Jul 18, 2011

If you read the link in Reply #5, it would answer most of your questions. An echo charger would limit charging to the reserve bank, and isolators are so way 60's technology that you should simply move your alternator output to the house bank, get it off the 1-2-B (or other) switch(es) and keep it simple.

Doesn't matter how long it's worked for you, isolators take out way too much voltage.

Here's another link for you: http://c34.org/bbs/index.php/topic,5977.0.html

Maine Sail · Jul 18, 2011

capta said:
I believe I must switch sensor/exciter lead from eng to house as suggested

Yes this is a fairly critical thing to do....

capta said:
but w/ a house bank of 700 amps & the eng (a measly 4D) rarely needing much charge of course, what will keep the eng battery from getting over charged?

They will only be the potential for over voltage, not current, if the absorption voltage for the house bank is set higher than gassing, which on flooded batts is about 14.4v. If the regulator is running at 14.2v as you've mentioned then your start battery should not suffer any critically detrimental consequence and could likely run like that for five plus years or more.

capta said:
The isolator keeps the systems separate, but what would limit the charge to the eng battery if house required, say, 80 amps?

The battery limits what it takes from the alternator on its own. The worst you can possibly do is supply a voltage above the gassing range for to long and boil off some electrolyte. If you do just top them up more often.

capta said:
I've run to the Carib & back w/ it this way w/o a problem, but I think the system could be improved.
Thanks again for the imput.

An ACR (automatic combining relay/voltage sensitive relay) or an Echo Charger are the typical installs these days. Diode isolators are really an older technology that are rarely used anymore. With an ACR or Echo charger you will not face the issue of over voltage to a bank not needing it...

mitiempo · Jul 19, 2011

The Echo Charger doesn't relate to the alternator, whether it is 25 amps output or 200. It relates to the battery it is passing the charge to - the start battery, which will be down 1 or 2 AH from engine starting.
A combiner (ACR) will not let power flow from one bank to the other as it only closes when it sees a charging voltage.

Your wires are also too small a gauge. For a 6' run (12' there and back) and 110 amps 6 awg is required for a 10% voltage drop. For 3% voltage drop the wire gauge required is 4 awg and were it a foot longer it would require 2 awg. With 8 awg not all of your alt output is getting to your batteries.

With respect, an ammeter will show how much is going in/out of the batteries. A voltmeter can tell you state of charge after 12 hours of rest not using the batteries. A battery monitor will give you information about your batteries you just don't have currently.