Battery charging

[Connerkip]

On the C30, there are three banks of batteries, totaling six batteries.

(4) house
(1) engine
(1) thruster

When replacing batteries I have seen it said many times on Tugnuts, to change the full set. What is the set? In my case, two of my house are bad. The engine and thruster batteries are both good. Do I need to change all four house? Or Change all six? And why?

I'm pretty certain I should not combine the good engine and thruster batteries with the two good remaining house batteries, and just buy two new batteries for each of the engine and thruster.

A related question. Does the engine alternator charging pass through the same charging relays as the charger/inverter, cycling through each bank? Or does the alternator charge all six batteries at the same time?

Thanks

 

[Larry H]

Short answer, change the four house batteries, they act as a single battery. Keep the start and thruster batteries till they start to go bad.

The new house batteries should be identical and have the same build date.

 

[NorthernFocus]

A "bank" of batteries typically means a group wired together with no isolation switches, etc, between individual batteries. In the case you describe you have three banks, house, engine, and thruster. Conventional wisdom is that all batteries in a bank (as described above) should be replaced at the same time. The reason is so that the batteries all have the same history and therefore same level of health. A single bad battery in a bank can ruin the entire bank.

Which begs to question, what do you mean when you say you have two bad batteries in the house bank?

Others with more knowledge of the Cutwater wiring will have to speak to the question about charging. Typically there are isolation switches between banks to protect from a single bank drawing down the others. When everything is healthy the isolating switches should close and allow the alternator to charge all at once. The A/C charger is usually wired separately.

 

[Red Raven]

My thoughts,
It depends on the condition of the remaining "good" batteries.

1) If the start and thruster batteries and two good batteries test as near 100% good and are less than 4 years old then you could combine the four of them as your new house bank and may get a few more years out of them. Just realize weakest battery will determine the performance of the house bank. Then buy just two new batteries for start and thruster. This option is the least expensive but most risk.

2) If the "good" batteries are less than 4 years old and otherwise healthy when tested then you could use the best two of these as your start and thruster batteries and buy all new house batteries. The new house batteries would have to be the same type as the old batteries.

3) If the "good" house batteries are suspect but the start and thruster batteries test good then just leave the start and house as is and buy four new house batteries.

4) Change them all out for cheap flooded batteries. I'm sure other Tugnuts will chime in with votes for for this option.

If it were me it would depend on the assessment of the remaining good batteries (i.e., thus choosing options 1 or 2) and how much I was willing to deal with the potential issues vs. just going with a regular replacement program of cheap batteries (i.e., going with option 3 if the four good batteries are questionable and committing to a regular battery maintenance schedule of the cheap flood batteries).

As to the "why":
For charging, all the batteries need to be the same type, because the battery charger only runs one charging program based on battery type.
During discharge the poorest battery will determine the performance of a bank that are connected directly. The good battery's performance will be wasted trying to prop up the poor battery. The Thruster and Start battery are discharged independently (not connected together except for during charging) from the house bank so their condition will not affect the house bank.

Curt

 

[Cutwater28GG]

I'd do what Larry H suggests

Im surprised 2 of the house batteries are bad after 2 years? any indication why? I assume these are the AGM's?

 

[Connerkip]

Yes AGM, they are 3 1/2 years old. The factory had improperly wired the solar panel, and there was no output. During that time of troubleshooting and discovery, I experienced several low voltage situations, which I suspect compromised the house batteries. Long annoying story.

 

[knotflying]

You got some good advice here. One of the suggestions was change everything over to flooded. As many know I am a proponent of flooded, your example is why. AGM batteries are great until they aren't. a few mishaps and they experience the dreaded results of replacement along with adding salt in the wound of the large expense. AGM batteries are perfect when logistics require mounting them sideways or on a sail boat that can heal over substantially. Granted on flooded you have to add distilled water occasionally, so access to caps is important, but there systems available to fill them even if there is limited access. And there is also the option of "maintenance free" So, for around $600 you can replace all six with Walmart flooded and with proper care they will last for five years and possible longer. I replace mine every three years regardless of their strength (overkill) and it is still less expensive than the AGM route.

As far as the charging and relays go, at any given time all of your batteries are joined and are being charged by the alternator when underway. In the event a bad battery or the house bank goes below a specified voltage, the relays recognize this and assume something is wrong and they will not allow that bad bank be coupled and charge. Depending on how your boat is wired, this also applies to charging while on shore power.

 

[Connerkip]

Thanks for all the help. I'm replacing the bank of four house batteries with four new AGM. I am keeping the existing engine and thruster batteries in place as they tested good.

 

[R21]

I've always had a problem with my R21 in that the trickle charger seems to charge one but not the other battery. Not sure why that should be so. But this year I bought a Genius GB40 lithium ion battery booster as an insurance policy. I'd recommend it to anyone. According to the specs it will start a 3-liter diesel or a 6-liter gasoline engine. That's more than enough for my 3YM30 Yanmar. And since it is so small and portable, I obviously have it available for my truck as well in the event of a battery failure. I once had a brand new truck battery die on me on a 2500-mile trip and I wish that Li-ion technology had been available back then. Regards.
Denis