Volt meter conundrum.

[DSigmond]

My 22 Cruiser has start and house batteries that are independent unless their switch is set to "Both" for charging while underway. I'm aware that a forgetful me could kill them both, but my conundrum today is: Which one does the dashboard voltmeter read? More to the point, can I get a dual meter to monitor them independently?[/i]

 

[thataway]

The "voltmeters" on consoles are noxiously inaccurate. Digital volt meters are far more accurate. I doubt that anyone can vouch for certain which battery, or both, if they are combined. Logic is that the large (not large enough) from the circuit breaker near the battery, is the lead to this volt meter--in that case the "house" battery. On the other hand, if the wiring of the voltmeter as so often is the case, is taken off the ignition circuit--it will reflect the alternator's output voltage.

I would buy two in-expensive digital volt meters from Amazon, such as: such as this Blue Seas.. Or you can get two little voltmeters, only 3 digits, for less than $15.

If you want to stick with one digital meter, then put in a "on-off-on" toggle switch below the meter, and push the toggle one way for house, the other for engine.

It is far better to put in a Automatic Charging Relay: Blue Seas for less than $100

Or better yet a Victron shunt or 702 volt/amp/state of charge meter, which will read two battery voltages, and the complete condition of one of those (should be the house battery) including amps in or out, state of charge etc. There are cheaper versions, such as For less than $40..

 

[C-Wolfe]

As always Bob comment are top notch and hopefully that answer you questions about monitoring your batteries.
I did run into the very issues you are talking about a couple of time on previous boat, fortunately my kicker had charging capability so I could get myself out of trouble like this without too much fuss. When I purchased my C-dory, I had a lot of corrosion on electrical outside of the cabine and decided to replace everything.
I went with a set up like this



I don't know if you have single or twin engines, I have twins. I have 2 batteries, one for each engine and pick one for the trip as my house, on a standard trip for me (2-4 days) I never touch the main selector switch. If I have too ( I did once but turn out the problem was the neutral switch) I can have either batterie start either engine, or also have either engine charge either batterie.
For the way I use my boat, this system works very good. I don't have to do too much monitoring since one battery should always be near 100%. I do have a digital volt meter with the on/off/on switch and even though I really like having it, I don't use it much.

 

[gstraub]

Usually the voltmeter is wired to measure whichever battery is switched on. If the switch is to "both", then it is usually reading the combined bank. This is because the meter is usually wired right into the bus. You could put in dual meters, but you'd probably then have to run two wires for the meters all the way back to the battery switch.

 

[Peter & Judy]

I like to use the KISS method whenever possible. My boat has two batteries that can either be used as a starter or house battery. I will alternate batteries when cruising so that both are charged and then dedicate one as a house battery when at anchor. The start battery is not used for anything except starting. I also have solar panels which will help maintain the charge when not cruising. My voltage meter is one of those little meters that fit in the cigarette lighter and cost about $15. I plug it in when I want to monitor the batteries and they work great. I keep one in my camper and in my truck as well.

 

[smckean (Tosca)]

IMHO, the most important thing you can do is what Bob mentioned:

It is far better to put in a Automatic Charging Relay: Blue Seas for less than $100

Otherwise when you combine batteries (really only meant for emergencies), and no charging source is present, you might often be connecting in parallel a high charged battery with a low charged battery (i.e., voltages very different from each other).....this is a no-no in the world of batteries especially if one of the batteries happens to be dead (i.e., very low voltage, say below 10v).

 

[ssobol]

... Otherwise when you combine batteries (really only meant for emergencies), and no charging source is present, you might often be connecting in parallel a high charged battery with a low charged battery (i.e., voltages very different from each other).....this is a no-no in the world of batteries especially if one of the batteries happens to be dead (i.e., very low voltage, say below 10v).

How is connecting two batteries via the Both switch position when one is highly charged and the other is discharged any different than using jumper cables to start an engine? Jump starting things is done all the time.

The advantage of the Both switch is that there is no chance for sparks or getting the battery terminals mixed up (once the wiring is done properly).

 

[smckean (Tosca)]

ssobol,

No different. Using jumper cables ain't good for the batteries either due to the large in-rush current from the high SOC battery to the low SOC battery at the moment such batteries are interconnected.

My point is that what you can do in emergencies, which happen very infrequently and for short periods of time, is no reason to design a system which allows the parallel connection of high SOC and low SOC batteries on a regular basis. You might jumper (with cables or a "Both/Parallel" switch) what? Maybe once a year, once in 5 years? To use the "Both" switch the way the OP does, one might interconnect high and low SOC batteries every day.

Better to isolate the batteries unless they are being charged -- which is exactly what an ACR is designed to do. (Note: even with a ACR, you may still need to jumper -- or use a "Both/Parallel"" switch -- if the start battery is dead and you have no charging source.)

 

[tsturm]

ssobol,

No different. Using jumper cables ain't good for the batteries either due to the large in-rush current from the high SOC battery to the low SOC battery at the moment such batteries are interconnected.

My point is that what you can do in emergencies, which happen very infrequently and for short periods of time, is no reason to design a system which allows the parallel connection of high SOC and low SOC batteries on a regular basis. You might jumper (with cables or a "Both/Parallel" switch) what? Maybe once a year, once in 5 years? To use the "Both" switch the way the OP does, one might interconnect high and low SOC batteries every day.

Better to isolate the batteries unless they are being charged -- which is exactly what an ACR is designed to do. (Note: even with a ACR, you may still need to jumper -- or use a "Both/Parallel"" switch -- if the start battery is dead and you have no charging source.)

I have been doing the switching between 1-2 & both prehistoric knuckle-dragger way for 40 years. When house batts get to 12v or so I switch to both before running for an hour or so. just had to change all 4 batts last fall 2ea G24 starting, 2ea G 31 deep cycles for house must be doing something wrong I only got 12 years out of the house batts & 10 years out of the starting batts. All lead acid:wink: :thup

 

[smckean (Tosca)]

12 years out of the house batts & 10 years out of the starting batts

That's fantastic. I get about half of that.

I think battery longevity depends a great deal on how you use the batteries; for example, primarily taking day trips, vs doing multi-day or multi-week cruises. Cruisers cycle batteries more often due to lots of "comfort" equipment (e.g, heaters, microwave on an inverter) on board which take down the batteries to say 50% SOC every night or day at anchor (indeed, many times multiple cycles per day).

 

[Peter & Judy]

12 years out of the house batts & 10 years out of the starting batts

I also think that battery longevity depends in part on how you maintain batteries. Last year was an expensive battery year for me. I had to replace two batteries on the boat, two batteries for the camper, the diesel truck also needed two new batteries as did the lawn tractor.

Most C-Brats seem to live in mild climates so battery maintenance is simple and longevity is long. I live in Alberta where winters are very cold, which is really hard on batteries and can shorten their lifespan considerably. It is important to maintain batteries, keeping them charged and preventing them from freezing when discharged. I keep a trickle charger or a solar panel on my batteries that I cannot remove in the winter. The batteries that I can remove, like the ones in my boat and camper are removed and kept in a warm building and periodically recharged. If I was living in a mild climate I would simply keep these batterie in my boat or RV and maintain them with a trickle charger or solar panel. Good batteries are expensive and a boat without power might as well be a hard to paddle canoe. I always have solar panels on my boat helping to maintain my batteries while cruising and at anchor.

 

[smckean (Tosca)]

Good batteries are expensive....

You can say that again! I use AGMs (on my boat lead acid don't fit properly and are particularly hard to remove to check fluid levels).

I just ordered two D34Ms for a mere $700!