Starting Battery Size (Ford Lehman 120)

I am re-configuring my batteries on my GB32. Current configuration combines two 4D house batteries for starting but then you use one or the other of those same batteries as your house battery.

My plan is to replace the two ailing 4Ds with four Tojan T125 Golf Cart batteries and then add a dedicated starting battery. I was thinking of using a single Group 31 but I have room for two group 31s.

Boat still has original Motorola 53 amp alternator. There is a nearly new, easy starting, 3.5KW generator on board that has its own Group 24 start battery.

Looking for a reliable start without over-kill.

Thanks

I have SP225s in my boat. It came with 2 4Ds for starting. It has built in fiberglass battery boxes so when I replaced them I stayed with the 4Ds just because it was easy. The group 31s should start a 120 easily. Personally I would go with 2 31s so as to have a backup if the battery shorts out or just dies. I would have them set up in 2 banks so that only one was online at a time and the other one as a offline spare.

A single group 31 is likely adequate for starting. I'd personally run the engine power feed from the start battery through a 1-2-both-off switch. Switch is normally left on "1" (engine battery) and "2" gets connected to the house battery, allowing the house bank to be used for starting if needed.

I have a single 120 Lehman.

I took out a 4D and replaced it with 2 Group 31 batteries in a parallel configuration 19 years ago. Have replaced the original G31's once.

The G31's start the engine, generator and power the windlass and thruster.

It's been reliable.

Im an electrician who works in renewable energy. I run two group 27 Concorde AGMs as my starting battery, wired straight to the engine. I have a single engine 120 in my 36’. House bank is a pair of 4D Concorde AGM and gen battery is a single group 27 AGM. The pair works great as the starting battery, though I imagine one would do the trick. My house bank has an interlock to connect to the starting bank if needed.

The sealed AGM batteries do not need a battery box, I just strap them down and make covers for them to cover the terminals, makes a good mini workbench when I’m in the engine room.

Yes. The two banks will be combined for charging with a Blue Sea SI-ACR (Automatic Charging Relay) that will combine the banks once the alternator starts providing a charge.

If I put the 1-2-both switch to both the house bank will start the boat (if they are not dead from running the refrigerator) If they are dead then I can start the generator and sit there for awhile.

So you use 2 31s as a start battery and have another bank for the house or do you just have a total of 2 31s?

Forgot to mention, the previous owner had put in a high output Balmar, so I have dual alternators which I really like. The original charges the starting bank, the Balmar charges the house.

I use a lot of energy for refrigeration and freezer, I actually have another 12 Group 27 AGM under the bed in the rear cabin that I’m going to wire is as the house bank.

Avalanche said:

Forgot to mention, the previous owner had put in a high output Balmar, so I have dual alternators which I really like. The original charges the starting bank, the Balmar charges the house.

I use a lot of energy for refrigeration and freezer, I actually have another 12 Group 27 AGM under the bed in the rear cabin that I’m going to wire is as the house bank.

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I have two alternators on the single Lehman.

One 85 amp internally regulated for the 2 Group 31 starting batteries and one 150 amp and a Balmar regulator for the 6 golf cart batteries.

Avalanche,
You actually need a refer in Alaska...

Well, I can "better" most of you (I was going to say trump everyone but probably not appropriate) _ we have two SP 135s and each has its own 8D - yes, 8D - serious grunt there - way overkill I know but they sure fire up the old Lehmans without blinking

Brisyboy said:

Well, I can "better" most of you (I was going to say trump everyone but probably not appropriate) _ we have two SP 135s and each has its own 8D - yes, 8D - serious grunt there - way overkill I know but they sure fire up the old Lehmans without blinking

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Indeed! Don`t want to invite a trade war.
My IG has the same pair of 8Ds. Don`t forget they do house duty too.
Onan`s Manual advises a 150Ah/?6D for the 3cyl Kubota engined MDKD.

Brisyboy said:

Well, I can "better" most of you (I was going to say trump everyone but probably not appropriate) _ we have two SP 135s and each has its own 8D - yes, 8D - serious grunt there - way overkill I know but they sure fire up the old Lehmans without blinking

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And I thought my 4Ds were overkill. Now I have battery envy...

Comodave said:

And I thought my 4Ds were overkill. Now I have battery envy...

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But we have "battery envy" of you when we fit a fresh 8D, we replaced both this year. And the genset batt.

On a previous boat I had 5 8Ds. What a PITA when it came time to replace them. I hired a young guy to do it.

"if they are not dead from running the refrigerator"

Ser 31 are great start batts but die rapidly when run flat.

True deep cycle batts hate to be run flat , but survive the abuse a bit better.

If just 2 batts are for combined house and start work, 2 deep cycle 8D will have enough plate area to start most engines even down below 50% SOC.

Have you thought of installing a SOC meter ?

I think the question asked to lessen overkill.

To answer that. Pretty sure a group 24 battery works.

I called American Diesel and 2X I didn't understand their answer.

So I researched the starters used on Ford 120s. They only draw a little over 300 amps from what I could determine.

So anything above 400 CCA should work..and that is a small battery.

I didn't trust my math so I have been using a Walmart Maxstart rated around 900 CCA and it was perfect for about 7 years as I am on my second one. I think it's rated for diesel trucks and like a group 31.....maybe a tad bigger.

The new ratings on batteries mean nothing to me yet....it's a 50 something but overkill. 2 Batts or bigger is WAY overkill.

My boat has eight golf cart batteries for the house bank and NO starting batteries for the two Lehman 120s. Works just fine even when house bank is down to 40%. Many DeFevers are wired this way. In my opinion, a boat with a larger house bank having a starting battery is a waste. Others will no doubt disagree because the house bank might go dead and then how would one start the boat. Happens rarely but what if. In my case there are two options. One would be to use jumper cables from the two Group 27s that are dedicated to start either of the two generators. Or, two, start a generator and charge the house bank. There is no "right way" in this regard. Both methods work.

"2 Batts or bigger is WAY overkill."


Yes , But , a restart after running out of fuel, or a bad filter change might be easier with overkill.

Our boat came with an 8D dedicated to the genset only (!?!) and four 8Ds that served as both housebank and main SP135 starters. All diesels—genset and Lehmans—now start with a single Group 31 AGM. It’s topped off via a Balmar Duo Charge. Should it crap out, a flip of battery switch ties in the 1,250-AH housebank. So far, not a hiccup with this arrangement.

A Grand Banks has a set of relays that combines the batteries when starting regardless of the selector switch position. It works quite well and has since the early production runs. No good reason to completely rewrite the DC system unless you have cash to burn. Replace the batteries with what you take out and use the cash to fund work that really needs to be done.
Just my opinion as a guy who has been in your exact predicament.

I start my 8.3 liter 450 Cummins with a single grp 31. Starts fine even with engine at 45F temp. Backup is house batt, but never needed to use it. Starting batt also starts gennie.

Worst case if I had to crank a lot would be to start the gennie and let charger run for a while. But never had to do that either.

Cummins spec for the engine is 1800AH for a start batt. I am at about half that and it does fine.

Since my boat is a light planing hull, I try to minimize the weight. If I ran displacement speed I would probably use two 31's for the start bank. But the single works just fine.

I do have a digital volt meter on the helm that monitors all the batts, so charging status is always known. Can also monitor volts at cranking to see if it goes too low. That gauge is a nice feature to have.

FF said:

"2 Batts or bigger is WAY overkill."


Yes , But , a restart after running out of fuel, or a bad filter change might be easier with overkill.

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Just like any start battery, if right sized to begin with and kept charged.. plenty of cranking available for multiple attempts.


Upsizing is not a bad idea...but if a group 24 is OK, then 2 Batts or a 4D is a waste. Better to put it in the house bank and have the ability to connect banks.


Too often upsizing with this crowd gets out of hand.

I am going to install a Mastervolt BattMan Lite (State of Charge meter) on the house bank.

SailorGoneBad said:

I am going to install a Mastervolt BattMan Lite (State of Charge meter) on the house bank.

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You may want to take a look at this piece written by TF member CMS. If I was putting in a battery meter now, I would definitely use this one. I have a good coulomb counter SOC meter on my boat but am considering changing to the Balmar SG200 anyway.

https://marinehowto.com/balmar-sg200-self-learning-battery-monitor/

The Victron energy BMV 712 Smart meters allows monitoring state of battery with smartphones remotely, via built in Bluetooth, in addition to the monitor itself.

That is correct. The boat was originally equipped with a "charge divider" which, I assume, was a couple of diodes through which the alternator was connected to both batteries at the selector switch. And then the batteries were combined when the ignition button was pressed for starting. This "charge divider" was removed by PO for some reason and the alternator was only connected to one bank. By re-configuring I hope to get twice the house bank in the same foot print and an isolated starter battery. I will also fix the problem of the 2nd bank not being charged by the alternator.

FWIW, when it comes time to replace my 8D starting battery, I’ll replace with a single Group 31. I have a 5.9L Cummins engine. I also have the ability to combine the house bank for starting if needed.

I removed my “charge divider” because I decided that a dedicated house bank and a dedicated start bank with a battery switch made more sense for me. Nothing nefarious.

By the way, running your battery bank to 40% will kill it. A safe minimum number is 12.2 volts with no load.

Just as important as a LARGE battery is good cables.
This spring I had a slow start, then a no start.
My bank was 2 grp 31s and a grp 24 (That's what fit in the box). Voltage showed and measured 12.7 for the bank, 12.4 for the battery that the starter cables ran from.
Being a single engine, I pulled the starter and had it rebuilt, and they put on a new solenoid.
I measured voltage drop while the (rebuilt) starter was engaged. 3 volt drop. Not good.
Cables were original and actually looked pretty good.
I made up new cables and repeated the voltage drop test.
1.7 volt drop across the starter.
Drop along both the pos and neg cables went from .7 volts to .2 volts.