Complicated 12v to T105 conversion

[LLCoolDave]

So I'm in Rio Dulce, Guatemala. It's my first boat. I have 4 ACDelco group 27 batteries. 1 starter in the stern lazerette, two in the port lazerette (with room for one more), one in the head for the electric head and it connects to the windlass.

I have shore power and my charger/inverter failed and I'm sure the batteries were damaged, Fridge and freezer were running. It got to very low voltage. These 27s aren't real cruising batteries. I want to switch to trojan t105s. If I could find J150 or T1275 I would use those.

So with removal of the starter battery I can install four t105s and replace the head battery with another 27 for the windlass.

I heard from one person not to use a deep cycle setup to start an engine. It's a W40/perkins 4108. I heard from another person that it's a small engine and won't make much difference.

Second scenario is I replace the starter battery as is, build a new battery box for 4 trojans and eliminate the head battery and replace/use existing cable to power the head and windlass

I have a blue sea automatic charging relay.

Third scenario is I ditch the starting battery, relocate the blue sea unit wiring to the head and that becomes the starting battery, no need to build a new battery box. The starting battery would be far from the engine though.

I'm already installing my new charger/inverter

Just considering my options. All input is appreciated.

[smac999]

2nd unless the windlass is really far from the house bank. then maybe 2nd + keep windlass battery.


4 golf carts should start an engine. when full, but not after you drain them at anchor, which is the point of a house bank. only having one bank is crazy. you want the start battery in reserve, which is always full and ready to start the engine.

[john61ct]

Yes, common misconception.

Even a huge diesel has no issue cranking off a

large enough Ah capacity
high-SoC
and healthy (high SoH)

deep cycling bank.

Many owners like the security of a dedicated Starter bank, but that can often be centralized for multiple engines.

An alternative design would be a Reserve bank, with cranking loads easily switched between that and House to confirm all is well.

Critical House loads - "Essentials" circuits shoyld be switchable as well for getting back if House bank fails.

And a little portable LI jumpstarter powerpak can be kept charged and also regularly tested for belt & suspenders redundancy if the above is not considered enough.

[john61ct]

Best to invest in heavy enough wiring to consolidate all non-cranking loads, even high-amp ones to a single House bank, because Peukert.

Best if those loads are also supported in use by ICE sources running if practical.

But distances can be just **too** long, and sensitive electronics may be an issue.

[geoffr]

Generally you want a house bank which is deep cycle and a start battery/bank. For a thruster/windlass the ideal is large gauge wires to the house bank.

Having said that in our system we use a thruster battery and duo charger because I couldn't run the large gauge wires to the thruster.

We have the following (as a reference for you):
- 6x T105s for the house bank
- 1 AGM starter battery
- Thruster AGM battery in the bow

The two AGM batteries are charged via duo-chargers

Geoff

[roverhi]

I like your idea of using the windlass battery as your start battery IF the cable run can be done with proper sized wire. Assume the run to the engine will be about 15' or so which may be the same as the run to the windlass. Shouldn't be any fear of running down the start/windlass battery as most would have the engine already running before using the windlass.

No problem with deep cycle battery starting a smallish diesel like a 4-108.

[Cat36Mahalo]

Keep the same chemistry on all your batteries or use programmable dc-dc chargers. Different battery chemistries require different charging voltages and profiles.

[john61ct]

You can buy different batteries where the ranges overlap enough, long as the charge sources are customizable.

Starters don't warrant fiddly care anyway.

But DCDC chargers may be warranted by long run voltage drop anyway.

Biggest advantage of using the same deep cycling units for everything is redundancy, if cruising faraway primitive locations

[sailorchic34]

Four 6 volt batteries as a house Bank will have no trouble at all starting an engine even at 50% capacity.While I have a backup start battery, I have not used it in 10 years. I also have a dedicated windlass battery. I have a 2 Amp 3-stage DC DC charger for it that I got on eBay. Works like a charm.

[chouliha]

We only have 6v golf cart batteries and for the past 30 years never had trouble starting the engine with them. 20 of those years cruising.

[model 10]

Dave, screw the flooded battery idea and just go with a bunch of group 27 AGM's. All the wires and terminals will be the same, easy peasy. The idea that 1 group 27 AGM battery won't start your engine is goofy.

[john61ct]

I dunno what G27s are made by Odyssey or Lifeline.

The Odyssey PC-2150 are great G-31's for deep cycling use though.

But why would you want to pay so much more?

And any true deep cycling AGM may be hard to source in Guatemala. . .

[duckpond49]

An starter battery isolated from house bank is the best setup. Starter batteries are designed to deliver a quick 200A jolt and then recover quickly. Big deep cycle batteries can deliver large surges but don't recover quickly. I left the radio on in my truck yesterday for 5 hours and my truck wouldn't start. I put a small 6 amp charger on it for 45 minutes and was running again. Try that on a 400AH house bank and it would take 24 hrs.

[Moontide]

My guess is that the Group 27 are car batteries, not deep cycle. For a boat (IMHO) you really want true deep cycle (and not the ones that say they are "marine" and function as both.


Golf cart batteries are by far the biggest bang for the buck, and usually readily availalbe almost anywhere, although for long term ownership LiFePO (sp?) is starting to get closer.


Bill

[john61ct]

Originally Posted by duckpond49

An starter battery isolated from house bank is the best setup. Starter batteries are designed to deliver a quick 200A jolt and then recover quickly. Big deep cycle batteries can deliver large surges but don't recover quickly. I left the radio on in my truck yesterday for 5 hours and my truck wouldn't start. I put a small 6 amp charger on it for 45 minutes and was running again. Try that on a 400AH house bank and it would take 24 hrs.

Not just simplistic but wrong. Cranking even a huge diesel does not give a deep cycling bank anything to "recover" from, less than .0001% draw down.

As demonstrated by the fact those little lithium packs fit in your pocket can handle it.

The fact is your anecdote showed you using a small starter batt for deep cycling.

A large House bank should be feeding all other loads like a radio.

Having a Reserve that does not get used except in emergencies is in effect the same as having dedicated Starters, just sized bigger to also handle other essentials like safety systems, navigation etc.