SKI summed initial testing nicely.
I will post my tome regardless.
Lutarius
I’ll try to answer some of your questions without consideration of various SOC systems.
A question or so first:
- Did your system work before?
-Is this problem only recent or have you had some trouble before?
-What size is the alternator? Amperage output? What type and mfgr.?
-IS the alternator controlled by an internal regulator or has the alternator been fitted to be controlled by an external 3 stage regulator?
-How do you use the boat and has that use pattern changed recently?
If you want to monitor the actual alternator output in amperage you must install an ammeter in the alternator output line only. It is not practical nor is it good practice or safe to install an inline ammeter permanently. Rather what is used is called a SHUNT type ammeter. The shunt is a highly accurate, very low resistance resistor which at max ammeter capacity will produce a 50mV drop which the ammeter [really a voltmeter scaled to read out amps] then reads. They must be suitable for each other, ie. a set. Between the shunt and the ammeter gauge, quite small wires are used, usually 16AWG. The ammeter can be placed almost anywhere, on the panel or close by since it does not usually require constant monitoring.
For battery condition, ie. Charge state, that is where a SOC meter comes into play for continuous monitoring. I will not get into the argument about which mfg. or type is best. That won’t help now until your problem is repaired and until the problem is resolved and should be ignored at the risk of clouding YOUR issue.
The ‘test’ of your batteries that you did, terminal voltage after a charge and rest period, will tell you ONLY that the batteries are in fact charged. That test though cannot tell you about the actual battery condition. Even a battery with a failing cell, note: not dead, will show a DMM near perfect voltage. The reason is the DMM needs a tiny current to make it read, on the order of 1 or 2 micro amps. That current is so tiny that it will not affect the battery readout as even the failing cell can produce that level of current. At some point it will show but then almost always other troubles have shown up.
To truly test and assess a sealed battery condition, AGM or GEL, a proper LOAD test must be done or test by the use of a Conductance meter of good quality.
I asked about the alternator since it could simply be too small. It may have been OK for running under light load conditions and/or light recharge conditions. But if your running loads are heavy , the batteries are down substantially, and the alternator is not big enough, once the needs of the running loads are met there may be very little current going to battery recharge. In cases like this many, many, many hours of running will be needed and possible shutting off some loads so less current goes to the loads and more to the batteries.
This situation is often not of great importance if you are basically weekenders and then go back and plug the boat in. However, if you have changed your habits and are multi week holidaying or serious cruising then what was ok for week ends becomes a real problem for longer term cruising where you depend upon the alternator to do a serious recharge of the batteries and handle the running loads.
If the alternator is damaged it cannot produce what it should. That’s why I asked about the alt. capacity AND if the system worked ok before. There are several ways that can happen. Failing diodes, failing regulator or alternator damage to the windings from overheating.
Failing modes:
-diodes can fail open meaning no current from that diode which can actually cause a substantial reduction or current.
-diodes can fail closed/shorted meaning the same as above, allow some AC through which is bad, and leak backward when the alternator is off.
-brushes can get sticky or worn out causing poor, intermittent or no output.
-connections inside can come loose or break.
The alternator should be pulled off and taken to a good alternator rebuild and test shop where they can actually load it up and make it work for a while to also test for heating problems.
Alternator types also can come into play. ALL alternators lose output when hot, some by as much as 25% which may produce inadequate performance. Some alt. are built better than a standard alt. to survive without burning up. They can run hotter, have better fans for better cooling and are rated more conservatively so they can run for long periods and survive.
But first find out if the batteries are good, and the alternator that you have is good.
If what you now have is actually working as it should then you may need to assess the entire system for your current useage. A lot of people do not understand that the batteries get recharged by whatever current is LEFT OVER after running all the other loads.:
-Electronics – vhf, plotter, computer, refridgerator, freezer, gauges, stereo, radar, AIS ANYTHING that is turned on while running.
-Inverter/charger – will draw current to run itself unless truly turned off. If on standby it still needs some current.
-Engine – yes that alternator itself will possibly use some of its own produced current especially if controlled by a 3 stage aftermarket regulator. An internal reg. will steal current but you won’t see it at the output wire as it is gone before that. Any electronic control for the engine require power. Fuel solenoid energized to run.
-Lighting, heating. Even if run from the main engine or a generator the controls often draw off your battery system which means the alternator when running.
-Even your ACR/combiner uses some current to operate., for the sense function AND to operate the relay.
-When the ACR operates what current was going to the house batteries may be split even further.
-Literally any electric item that is NOT run ONLY by the generator.
If the alternator is not a H.D. unit and not big enough then what actually gets to the batteries may be far less than you think.
Your steps should be:
Pay attention to Ski's suggestions first and report back.
A real load test of the batteries
An alternator check, [Brooksie]
If all the above checks out then an assessment of your system for suitability/capacity may be needed.
Consider the alt. output ammeter and/or SOC meters only later. They would be a good addition but should not take your attention off the real problem untill that is solved.
