Battery charging

[Pelican]

I’m still learning the ropes on my 2006 22 cruiser Salish C. I have a couple of questions I hope someone can answer.

Do I need to leave the battery switches in the “on” position to charge the batteries from shore power? I have twin Hondas, so I have three batteries.

It seems like my onboard charger only charges the house battery. Could that be right? I checked the voltage on both engine batteries with the charger switch in the off position, then on position. No difference. Humm. I’m not the worlds most knowledgeable electrician, so maybe I’m doing or assuming something wrong here. Any thoughts?

Thanks, Tom

[smckean (Tosca)]

It would not be unusual for your charger to charge just the house battery leaving the engine alternators to charge the start batteries. However, there is no way to know how your boat operates without you tracing the wires to see the paths the electricity can take.

If I were you, I would draw a chart of where each wire directly attached to the battery posts goes (yes, all 6 posts). Start with the large cables since they likely don't go far and are easy to see. Somewhere along the line you will see that one or more of these wires (probably medium sized) goes to a bus bar which is a hefty strip of metal to which a medium sized wire goes from the battery, and from which several smaller wires go to all the other places in the boat. One of the wires (medium sized) will go to the charger either from the battery post or from the bus. Add all that to your chart when you can. Note that the pathways you trace via the wires will sometimes be interrupted by a switch. If the switch is closed, then you can think of the switch as not even being there. If the switch is open, then it is like the wire (and therefore path) stops there.

To answer your question for yourself, look at your chart and see how the electricity would flow from your charger to the battery(s). Remember electricity flows like water in a hose. It will ALWAYS go from one battery post thru whatever wires are attached and then back to the other post on the SAME battery. It's all a one way street, and what leaves the battery MUST go back to the same battery. A complication is that the path back to the battery is often accomplished via the boat's ground. Any particular wire returning to the battery may go to a nearby piece of metal, with all these pieces of metal tied together by one or more wires, which in turn go back the battery's negative post. That common pathway is the boat's ground.

Not on your boat since you have only 3 batteries each doing a separate function (engine 1, engine 2, house), but on other boats some batteries may be interconnected -- which essentially makes those batteries into one larger battery. You will see parallel connections btwn batteries -- positive to positive -- rather than series connections since smaller boats like ours are 12 volt systems (although a 12 volt boat can have two 6 volt golf cart type batteries serially connected to produce the equivalent of one 12 volt battery).

[thataway]

Tell us what the battery switches are, and how labeled. It is very possible that you can use a single output battery charger to charge all three batteries. (Not the best practice.). It is a good idea to top off the engine batteries periodically, but you should not leave all 3 batteries connected together for any period of time.

What battery charger do. you have? Most come with a guest charger. These often give up with time, and a better charger is used to replace the guest original. It is not advisable to leave the batteries sitting on one of the original chargers. If you have a "smart charger" which samples the battery voltage and comes on if it has dropped. There will be a small amount of charging each day. The smart chargers are considerably more expensive.

It is certainly a good project to both draw out the circuit and at the same time use a label printer to tag each wire.

[ggray]

As a shortcut, can't you just check individual battery voltages with battery switches off and the charger doing its thing? See which ones have elevated voltage.

I haven't studied how my battery system works. I need to. But when we get back to the dock and plug in, the battery charger red light stays on for a while.

[Barry Rietz]

Use a three terminal battery isolator and wire it as instructed. If the onboard charger is without faults and operates as it should, the "system" will work passively and not need maintenance. And it will not need to be switched off since the isolator uses "one-way" solid state switches known as "diodes". The circuit is simple and used in many mobile applications.

[thataway]

[Barry Rietz]

Unfortunately, I must disagree with my good friend Bob Austin and the statements he just made. As an example; "diodes do not drop voltage, resistors do". The use of a "multiple terminal" (3 or more in this case) battery charging isolator is the exact device our friend Tom needs to employ, nothing more, nothing less. In fact, from the brief description Tom gave in his initial posting, I would guess that he already has this system onboard but is not aware it exists! Tom, do yourself right and visit any workshop where mobile 12 volt systems are utilized. This way you will have an opportunity to confirm the foregoing as well as view an "isolator" and learn how one works.

[Barry Rietz]

Unfortunately, I must disagree with my good friend Bob Austin and the statements he just made. As an example; "diodes do not drop voltage, resistors do". The use of a "multiple terminal" (3 or more in this case) battery charging isolator is the exact device our friend Tom needs to employ, nothing more, nothing less. In fact, from the brief description Tom gave in his initial posting, I would guess that he already has this system onboard but is not aware it exists! Tom, do yourself right and visit any workshop where mobile 12 volt systems are utilized. This way you will have an opportunity to confirm the foregoing as well as view an "isolator" and learn how one works.

[thataway]

Sorry Barry, The isolators have been around for a long time. The voltage drop is about 1/2 volt. I have one sitting my my garage still. Rarely used today in this type of application, especially with the newest smart chargers.

[Barry Rietz]

https://www.youtube.com/playlist?list=PLcKJy0Frwc1jVWztG2apSbzS42ggLptN4

[smckean (Tosca)]

Now I'm really taking a risk . I'm going to disagree with both Barry and Bob!

Barry.....Your comment "diodes do not drop voltage, resistors do" is misleading. An ideal diode would not drop voltage as your comment indicates, but of course there is no such thing as an ideal anything. In the real world. diodes offer some resistance to current flow, and therefore drop the charging voltage from the charger to the battery by the half volt or so that Bob mentions. If you have a smart charger that is unaware that you installed isolators between it and the batteries, the smart charger will not be able to apply the right charge profile voltages to the batteries because the voltage it is supplying will always be that 1/2 volt or so less than what the battery needs. OTOH, when no current is flowing, battery isolators do not have the small parasitic current draw like do battery combiners (aka battery separators). Also, a small quibble....you state: "one-way solid state switches known as diodes". That's not technically correct-- diodes do not switch. Using the water/plumbing analogy for an electrical system (often a very useful technique), a diode is like a check valve (one way flow as you mention), but not like a valve that can turn on and off (switch). True, like a check valve that can "turn off" the water flow in one direction like a valve; in a similar fashion, a diode can substitute for a switch in certain DC applications, but it is not a switch.

Bob.....multi-output chargers like the ones you mention do not really "treat each battery as a unit". Such chargers are really just a single charger with built-in battery isolator diodes so that current can not flow between the batteries connected to each of the outputs. The net of this is that a multi-output charger must be at the same position on the charging profile for all the batteries at any given moment in time regardless of each battery's state of charge (SOC). A charger that truly "treats each battery as a unit" would be able to supply the proper amps to each battery according to where each battery is on the charging profile given its current SOC independently of the other batteries. (Note you could even have different battery chemistries on this truly "treat each battery as a unit" charger.) There are such truly independent chargers out there, but they are really just multiple chargers in one housing, and are therefore proportionally more expensive. OTOH, the multi-output chargers like you mentioned do eliminate the unaware smart charger + independent isolator voltage drop problem, because this type of smart charger "knows" that the built-in isolator is there, so the charger can pump out slightly higher voltages to compensate for that known voltage drop due to the built-in isolators.

As the saying goes.....nothing is a simple as it seems .

[thataway]

Smckean, I don't disagree with you.

However the $670 Blue seas charger in its specs states:

[smckean (Tosca)]

Bob,

Interesting. I just took a look at these Blue Seas P12 chargers. I am no full blown charger expert, but I have studied up on this stuff a fair bit. Frankly, I don't think this charger changes the fundamentals of this discussion.

As far as I can tell, Blue Seas has introduced a clever technology that does not truly "treat each battery as a unit" , but it does take the typical smart charger one more step in that direction. I'm not 100% on this, but looking at the manual for these chargers, it looks to me like their clever "trick" is to indeed have a single charger (note they do not claim you can have different chemistries for each bank....that's the clue....even though you can manually set voltages), but they have added some electronics that senses when any of the battery banks is finished with its bulk and absorption phase; it then stops charging that bank until all the other banks catch up; then it applies the float voltage to all the banks at once. Something like that anyway. Clever.....by doing this, they avoid the worst part of a multi-output smart charger applying a higher voltage and current flow to a battery than it should during the float stage (given that some other bank is still in absorption) without having to have separate chargers for each bank.

Of course, you can always add fancier technology to approach the ideal, but it pretty much always costs more (in this case a $600 to $800 charger depending on max amps).

[gulfcoast john]

Seven years ago I replaced the Guest charger with a Blue Seas P12 40 amp charger (since the maximum bank for the 25A P12 is three Group 31 batteries...that’s what we use, but wanted the faster charging option). I don’t know or care exactly how they implement it but their claim (manual page 22) that “due to the P12 Battery Charger’s ability to optimize charging for each battery bank”…

Our boat was wired for a House plus a battery for the starboard and separate battery for the port engine. The windlass is on the House as well as the fridge and all other loads. Every year I rotate who gets to be the House battery this year, and boy do the Engine batteries whine and complain about it when it’s their turn. These group 31 Northstar AGM’s are now going on 5 years and still load test great. I credit that ability to adjust charging for the poor House battery. The extra expense for the additional capability seems worth it to me.

When the PS12 died under the 5 year (!!) warranty, I called their US tech support and they sent me the same day a new one Fed-Ex with a free return shipping label, saying ‘put the old one in the box when the new one comes in’. We didn’t miss a day of boating.

Buy quality the first time, it’s often worth it.

Cheers!

John

[hardee]

Good products and good business decisions go a long way towards making happy customers. And happy customers will do two things: Return with more business, and tell others, (at 1/10th the rate of unhappy, unsatisfied, disgruntled -- for any reason customers) about how bad the service is whether the service or product is good or bad.

Harvey
SleepyC