Alternator only charges 'Start' battery not house bank. How to add them?

[roland stockham]

1-2-both switches used to be popular in Europe as a cheap option (i'e' lots of builder fitted them). They have the drawbacks mentioned above but have also been know to cause fires. When you turn it to both you cause a dead short across the batteries, it is never good for them but if one is charges and the other is flat you dump the load from the charged on. That can mean several hundred amps and the wiring catches fire. The correct process is to charge each battery separately always shutting the engine off before switching (otherwise you can blow the alternator diodes) and only switch to both when all batteries are fully charged. So are you really always going to do this?
VCR's are a simple solution that works well but carry a spare as they do fail. They are also expensive but potentially save other costs.
Diode blocks are cheap and reliable. Although they can fail never heard of one overheating so they seam very safe. The issue of voltage drop puts people off as the alternator needs to run at higher than 'standard voltage'. For me this seems to be a non-issue because NO machine sensed alternator will effectively recharge a battery, they are designed to float charge a full one. Also very few basic installations have as little as 0.7v drop in the wiring. To make an effective system you need a battery sensed 3 step controller which then makes the diode drop insignificant, alternators happily run at 15-16v.
There are now two other options. Batt - batt chargers and true "0" drop distribution blocks which are effectively solid state VCR's. Both of these are expensive and have advantages in emergency vehicles but I don't see them as useful on a boat.

So my advice would be; If you only occasionally charge from the alternator and are mostly plugged into the dock look at VCR's as a cost friendly simple option. If you are regularly away from the dock and using alternator charging fit a 3 step battery sensed controller and choose from VCR's or diodes. Avoid 1-2-Both switches on anything bigger than a day-sailor.

[tinkrman69]

from your drawing you have about all you need. altho it would be nice to know the output amperage of the alternator and the amp hour rating of the Batteries in the house.

assuming you have 50 amp or more alternator and say 3 m27 led acid house batteries at say 120 amp hours each run batt 2 and 3 parallel...run an extra cable from pos to pos and neg to neg on those two,to accomplish that... we'll call this house bank 1. run a cable from pos on start batt to no1 post on switch 1 and a cable from sw1 common to sw2 common then run a cable from pos on house bank 1...either from no2 or no3 on that bank which ever is easiest, but not from both...to sw2 post 1 then a cable from bat 4...call this house bank 2... pos to sw2 post 2.

when ready to start the engine turn sw1 to position 1 and sw2 off. start engine and observe amp meter on engine control panel. when the amp draw has lowered to about 5 or 10 amps turn sw2 to position 1 and charge house bank 1. when the amp draw has lowered to ten or so amps you can switch to both on sw2 or over to position 2 and charge house bank 2 alone. you can also use the house batteries to assist the start batt in the event of a low start battery. don't try to start out charging all the batteries at once as you'll over load the alternator. if you keep the maintenance on the batteries...ie...charge and water...and this procedure of operation you'll have no problems and the expenses will be minimal. try not to drain batteries lower than 60% of their charge....12.3 to 12.4 bigger batteries increase that by point 1

the other methods are good for automation, but cost and not just money for the components. extra circuitry uses more juice. also if it breaks down and they do, you'll have to rewire till you get a new one or have no juice. every thing costs in life. you can spend money or spend labor. this labor is minimal. this technology is old and simple. it has never failed me and I earn a few bucks fixing all the newer technology on other peoples boats ;-)

[tinkrman69]

oh, do you have a charge controller on the solar? if not you should get one as the 17 or more volts coming out of the panels will cook your batteries.

[kas_1611]

Definitely recommend the Nasa Marine Battery Monitor (BM1) to keep an eye on your house battery charge and monitor the actual amps being drawn out or put in. Since fitting mine it has been a revelation on how much items draw and how much my panels can put in. Amazing what reducing the backlighting on the chartplotter does to the draw for example. The BM1 can also display your starter voltage with an extra wire which is probably worth doing.

I'm also considering fitting the mini version to my Thruster battery to be able to watch its condition.

Can you explain further on your 3 house batteries? Are these all "house" in which case they could be wired in parallel to give a much bigger "single" block in terms of amps or are they for specific duties, such as thrusters or windlass? This might help the collective braincells come up with a simple but effective system for you.

Keiron

[lmantuano]

Originally Posted by skipmac

Using a diode isolator is quick and simple but standard silicon diodes drop 0.7V so you're losing some of your charging voltage. A Schottky diode is lower but still 0.3V. Either way you will reduce the rate of charge. Better to go with one of the battery combiner options.

G'day SkipMac (MaineSail, and anyone with some electronics understanding/interest),

all true BUT, have a look/google "ideal diode", tiny little ICs which, in conjunction with power MOSFETs and a couple more components, will emulate power diodes with almost zero volt drop.. LTC4412, 4352, 4358, MAX16915. Datasheets and Application Notes a good source of circuit design options..
I bought some 4412s and I'm about to start making some test units in the 60-80Amp range, when I get some time.

lm

[skipmac]

Originally Posted by lmantuano

G'day SkipMac (MaineSail, and anyone with some electronics understanding/interest),

all true BUT, have a look/google "ideal diode", tiny little ICs which, in conjunction with power MOSFETs and a couple more components, will emulate power diodes with almost zero volt drop.. LTC4412, 4352, 4358, MAX16915. Datasheets and Application Notes a good source of circuit design options..
I bought some 4412s and I'm about to start making some test units in the 60-80Amp range, when I get some time.

lm

Interesting but my question is what advantage would this setup have over a Echocharge, Combiner or one of the other devices already on the market that sense voltage and connect two battery banks automatically? Would it be cheaper perhaps?

[lmantuano]

Skipmac,

Sure, no comparisons with the smart devices, I should have pointed out I was referring specifically to power diodes (Silicon, Schottky..) replacements and in reach of DIYers.

I believe some commercial versions are also on the market, i.e. 0-volt splitters from Sterling..

Cheaper solution? I guess $20-30 in components and your time to put it together?

Add smarts with Arduino or PIC..?

This is the 2007 article that got me interested, much water-under-the-bridge since...:

Circuit - Two 12v Battery Isolator uses a LTC4412 - Hobby Circuit

lm