How Many 8d's do I need

[Robby]

To safely operate my 43DCMY?My inverter is dead and we don't plan on replacing it anytime soon.We now have 4 8d's 3 of which need to be changed out.Your thoughts would be appercited.Robby

 

[Freeebird]

Maybe I'm missing something, but if you're on dockside power or running your generator while underway, what difference can batteries make if you don't have a functioning inverter?

 

[Freeebird]

Oh yeah, if 3 of your 4 batteries are shot, you need to buy 4 new ones. A weaker, older battery will just pull down the one you tie it in with. That's just to operate the boat, but that still doesn't address your inverter deal. You're not talking about a bad charger, are you?

 

[fissioneng]

I had no inverter and got by with 3 8Ds. Two on the port bank as house/port starting and just 1 8D on starboard (it only starts the starboard engine and generator). Not sure how your boat is wired. One 8D was plenty to start my Cats.

 

[SeaEric]

My 41 TC runs on 2 8d's (port and stbd) and a small dedicated genset start battery. The 8d's each start one engine and the house load is switchable from one to the other. 4 8d's was AFAIK the standard setup on 43 DC's but they will run with only 2.

 

[Freeebird]

You can certainly run on just three (I do), but the boat is obviously already set up for 4, so why change anything unless you're just trying to save a few bucks?

 

[Dan Mapes]

We pulled the cables over to the port side and ran them such that each engine had one 8D. We never had a problem starting 6-71TIs in Florida. The two 8Ds that were freed up on the stbd side drove our inverter/charger and the house. The engine batteries had their own charger.
Without knowing how things are cabled up, if you have three in parallel they should all get replaced and replaced with the same type/size.

So what do those 3 8Ds run?

 

[Timeout]

I had 4 also and had problems keeping them in shape. I believe they were beating each other up. Got rid of 2 so I ended up with one on each side and everything has worked well for years. When I replaced the generator, I added a group 27 just for the generator with a crossover switch to the port 8D just in case but have never had to use the cross over. The 2 remaining 8D's are now over 6 years old with no problems so I feel that was the right move.

 

[Robby]

We pulled the cables over to the port side and ran them such that each engine had one 8D. We never had a problem starting 6-71TIs in Florida. The two 8Ds that were freed up on the stbd side drove our inverter/charger and the house. The engine batteries had their own charger.
Without knowing how things are cabled up, if you have three in parallel they should all get replaced and replaced with the same type/size.

So what do those 3 8Ds run?

We have two 4d's one for each engine start.The four 8's are for the house bank and the inverter storage.We have not charged the 8's in about a week and they are still at about 12.7.If we don't replace the inverter will one 8 run the heads the lights and the bildge pumps in a safe and reliable manner?

 

[Freeebird]

We have two 4d's one for each engine start.The four 8's are for the house bank and the inverter storage.We have not charged the 8's in about a week and they are still at about 12.7.If we don't replace the inverter will one 8 run the heads the lights and the bildge pumps in a safe and reliable manner?

I'm sure Bill installed extra batteries to provide the necessary capacity to allow that inverter to power everything that's tied into it when the boat wasn't on shorepower and the generator wasn't running. With that, you won't need the extra batteries just to run your DC items. Yes, one battery will run those items safely, but you need to keep a charge on it when you're hooked to shorepower.

As stated above, one battery per engine and one for the generator is all you really need. Just make sure nothing else is connected to the dedicated generator battery. That way you'll always be able to charge the other two batteries in the event you kill both while on the hook for an extended period of time.

 

[Robby]

I'm sure Bill installed extra batteries to provide the necessary capacity to allow that inverter to power everything that's tied into it when the boat wasn't on shorepower and the generator wasn't running. With that, you won't need the extra batteries just to run your DC items. Yes, one battery will run those items safely, but you need to keep a charge on it when you're hooked to shorepower.

As stated above, one battery per engine and one for the generator is all you really need. Just make sure nothing else is connected to the dedicated generator battery. That way you'll always be able to charge the other two batteries in the event you kill both while on the hook for an extended period of time.

As you know we have a separate gen start battery.

 

[Boatsb]

You Need Enough To Carry The House Load.

I know we all have different boats and different uses. If you use a lot of 12 volt items and power refrigerators one will not be enough to power the house load.

 

[Freeebird]

As you know we have a separate gen start battery.

I was just referring to twin engine boats with generators in general. No need to tote all those extra batteries around if you're not going to use the inverter. Keep the three best ones and maybe a fourth to tie into your house battery. If you just use three batteries, you don't have to worry about a weaker one pulling down a strong one.

 

[Byresch]

We have two 4d's one for each engine start.The four 8's are for the house bank and the inverter storage.We have not charged the 8's in about a week and they are still at about 12.7.If we don't replace the inverter will one 8 run the heads the lights and the bildge pumps in a safe and reliable manner?

Is the inverter an inverter/charger or just an inverter? You will need something to keep your one battery charged to run the lights and bilge pump. Do you plan to buy a charger for the one 8d you plan to keep?

 

[Robby]

Is the inverter an inverter/charger or just an inverter? You will need something to keep your one battery charged to run the lights and bilge pump. Do you plan to buy a charger for the one 8d you plan to keep?

We actually have an inverter/charger and a wall mounted unit.I can choose which one I want to m use.