JB, Your other option is an automatic charging realy. This unit will automatically connect the two banks when there is suffiient output from the alternator to charge the house batteries. It also has a connection to the 'start' position on the key switch which will disable the connection when you are activly engaging the starter on the engine. The other benefit to this type of relay is that it will allow you to connect one 120V battery charger to the boat and charge bots battery banks without ever having to move your switch. I would not trust myself to put the switch into engine only mode every time I am starting. You are correct about the starting currents on the system potentially damaging your expensive electronics.
On the issue of which battery will get the juice from the alternator I will offer this advice. A battery is not only a power source, but is also a power user (even if it is fully charged). All batteries have an internal 'resistor' that draws current. This is not an actual resistor, but is simply an artifact of the way batteries work. When the alternator is running the voltage regulator will atempt to maintain 13.4 ~14.4 votls or so depending on the model. This is more than enough to initiate charging in a 12V battery. At full charge a 12V battery is actually 12.6 volts. Since the alternator outputs a voltage higher than this the battery will accept current. If both battery banks are in parallel and the house banks are 1/2 full and the starting battery is 1/2 full, each battery will pull enough current from the alternator to charge itself. If you have a 100 AMP alternator you would need 10 completely discharged batteries connected to it to run out of current and have problems. The only real problem with having the two banks in parallel is when one of the banks is completely shorted out and will draw the alternator and other battery down. This situiation shoudl never occur because if one bank is shorted, it won't work anyways. The long and short of it is, if the engine is running (and not actively starting) there is no problem leaving the two banks connected togather all the time. Be careful though if you have two different battery chemistries, not to leave them in parallel while the engine is off. The different kinds are; lead acid (both starting and deep cycle), Gel cell (Optima brand), AGM or absorbed glass mat (expensive). Trojan makes both conventional Deep Cycle and AGM types. For more info on Automatic Charging Relays go here: http://bluesea.com/viewresource/57 By the way don't feel too bad.. I live in the Atlanta area and we are expecting 2-4 inches of snow tomorrow and it is supposed to stick around for a couple of days... Strange weather this year... We just had tornados last week! Victor On Feb 27, 11:49 am, JB <[email protected]> wrote: > Tom and Victor, > > Thanks so much for your timely and informative responses. The house > batteries (deep cycle) are separated from the starting battery. The > only time they would be connected in parallel would be if I had the > battery switch set to "both". The boat's engine can actually be > started on the house (#2) setting but this would be undersirable since > it consists only of deep cycle batteries and the boat's electronics > are connected only to this circuit. I don't want to unnecessarily > expose the electronics to voltage or current fluctuations. If I am > anchored, I would only have the battery switch set to #2, thereby > isolating my starting battery from any current draw. > > My quandary is this: I will start the engine on #1 battery (starting) > only.and then let it recharge. The starting battery is normally > charged before the engine is warmed up. I could then turn my battery > switch to "both" which would connnect the house batteries and starting > battery in parallel. The alternator could then start charging the > house (deep cycle) batteries. Theoretically or at least it should be, > the alternator voltage output is higher than that of the batteries. > Hence, since the starting battery is charged at this time, most the > current would then be directed to the house batteries for charging. > For additional protection, however, would it be better to install a > dual battery isolator that basically consists of 2 diodes that will > not allow current flow from the stronger battery to the weaker battery > through the charging circuitry? I am not sure this is necessary or > desirable given I can separate the circuits manually by my 4 position > switch. ( "off", #1, "both", #2) Most RVs are wired with the dual > battery isolator. Any ideas? > > Tom, as I write I am watching someone ice skate on the lake in front > of the house. I envy the warmth of Florida right now. However, I > will be spending a week in the Ten Thousand Islands area during the > middle of March, so my view will change a lot. Only trouble is, my > father-in-law has a house right on the water with a channel that leads > all the way out to the Gulf. Sounds good, but he sold his boat two > years ago. Makes no sense! > > Thanks again, > > J. Black > > On Feb 27, 4:42 am, flitebuilder <[email protected]> wrote: > > > > > JB, > > > I have done a lot of research for my 36' SS. It has 4 12 volt systems > > and here is what I am going to do. > > > 1. Start battery for each engine > > 2. Start Battery (smaller) for the generator > > 3. House batteries (not sure what batteries yet, will be determined > > by remaining budget at end of re-fit. > > > The two main engines will be seperated from eachother with cables from > > thier respective batteries. There will be a battery combiner switch > > between the batteries. This switch will be in the engine > > compartment. The supply for the switch will run to a combiner switch > > at the helm that will allow you to connect the engine(s) to the house > > circuit. If on 1 or 2 then either the port or starboard engine will > > be connected to the house batteries for emergency starting purposes. > > Normally with everything working properly the engines will be left in > > parallel all the time and the switch turned off when not in use. > > There will also be plain on / off switches for each engine battery to > > turn them off during storage. > > > On the house circuit there will be an automatic charging relay that > > will automaticlly connect the engine(s) to the house batteries to > > charge them. This unit has starting isolation so that when the > > engines are starting the relay will not connect the two banks. The > > house circuit will also have the ability to be charged froman on-board > > battery charger. > > > The generator 12V circuit will be completely isolated from the rest of > > the boat. I will have jumper cables for emergency puroses though. > > > In normal operation you will get to the boat and turn on the two > > battery switches for the main engine batteries, switch the 120V system > > from shore to gen, and prepare to leave... If there is a problem with > > the main engine starting batteries there will be a very fast option to > > start from the house circuit. > > > For more information you can look on Blue Sea Systems website. they > > have some great information on boat wiring. Of course they are > > wanting you to buy thier stuff. I do reccomed thier products as I am > > very impressed with the way they are engineered. > > > I will be posting my boats wiring diagrams soon. I am still working > > on them. I am re-engineering the entire system. > > > hope this helps, > > > Victor- Hide quoted text - > > - Show quoted text - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "UnifliteWorld" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/UnifliteWorld?hl=en -~----------~----~----~----~------~----~------~--~---
