Starting Battery Size (Ford Lehman 120)

[Shay]

Single start battery

My previous Defever 49 came with 2 8D batteries on each Perkins 130 engine and a 5th 8D to start the 12.5kw generator. I rewired the boat so I had a dedicated house bank and 1 group 31 Duracell AGM start battery from Sam. The single start battery started both Perkins and the generator. Worked very well. I did have a AB switch that could be used to start from the house battery is needed but in 7 years it was never needed. I also had a combined to combine the start and house battery for charging.

Shay

 

[Comodave]

When we bought our boat with SP225s the PO had been running 15W40 for 15 years. There have been no problems so far so I continue to use the 15W40. I talked to Bob Smith at his last seminar about it and he said it was OK.

 

[Alisske]

I have 120 Lehman single in my 26 Groverbuilt. I have two series 31 AGMs on a 1-2-both switch.

I have to admit, I wish they were bigger. I switched from a 55 amp alternator to a 90. I think it helped keep them topped off. That being said, I travel a lot and for many years and had 2 engine problems while on the water. One diagnosed within 15-20 min, with minimal start and stops. All good. Second one took 2 hours and multiple engine turnovers (not a ton, but maybe 12 attempted starts.) I had to switch to “both” and was running out of juice when it finally started. This was 8 hours in on a 12 hour leg of a trip, so both batteries where charged to the top. (And batteries where bought within the same year as trip)

If I were to do it again, I would go bigger.

I am having battery envy reading this, lol.

 

[SoWhat]

The 1978 120 Lehman manual recommends single weight oil API classification CC, CD or Series 3, all obsolete. For 32 to 90 degrees 30 weight. Over 90 degrees 40 weight.

And if you didn't use CD in the turbo your warranty was voided. The engine would be ruined according to ADC. According to that theory, all lehman turbo's are ruined because CD spec is obsolete and you can't obtain it.

Back in the day of flatheads I remember the dilemma upon finding the shelf empty of 30W. Should I but 20W? I might ruin the engine! Then I'd move on to cleaning the brushes.

Technology has moved on and ADC isn't always right.

 

[Peter B]

Looking for a reliable start without over-kill.

Thanks

I had a 120hp Lehman in the CHB34 I had, and found a maintenance free 150 CCA truck battery did the trick very well. Your plan of having it separate from the house sounds ideal. That's how mine was configured. I then knew it would always be ready to start, as never used for house consumption.

 

[steve Dublin]

I had that setup on my C-380 sailboat. T-125s in series then paralleled and a separate start battery that I kept fully charged. Worked well. Can send you a pic if you want.
Stevedublin@bellsouth.net

 

[garycasey]

I think yours is a good idea. I did essentially the same thing to my NT 32. One starting battery is connected live to the engine and the other battery bank runs the house. They can be tied together if necessary to "jump start" the engine. Works great.

 

[FF]

"One starting battery is connected live to the engine and the other battery bank runs the house. They can be tied together if necessary to "jump start" the engine."

A simple method of keeping track of the house batts , if you dont have a SOC meter, is to switch the daily start to the house batts and observe how well it starts.

Usually if the house set has not been over discharged the engine will start as normal. And the house will get a great charge when the engine is running.

 

[clyde]

the only starting batt i would use is a group 31, with studs...clyde

 

[clyde]

or 2 group 31`s together...lotsa amps...clyde

 

[catalinajack]

I don't have starting batteries, just a 932 ah house bank. On one occsion, I mistakenly depleted the house bank down to 20%. My two Lehmans started just fine with no perceived difference in starter speed. With this kind of reserve why would I want to introduce the complexity (and space useage) of having a starting battery of any size. In the unlikely event that I run my house bank down to uselessness, I'll simply start one of my generators or jump start the Lehmans from the generator starting batteries (two Group 27s).

"One starting battery is connected live to the engine and the other battery bank runs the house. They can be tied together if necessary to "jump start" the engine."

A simple method of keeping track of the house batts , if you dont have a SOC meter, is to switch the daily start to the house batts and observe how well it starts.

Usually if the house set has not been over discharged the engine will start as normal. And the house will get a great charge when the engine is running.

 

[rslifkin]

With a very large house bank, yes, starting power is nearly assured as even very low batteries will have enough.

However, I still like separate starting batteries (at least 1 even if it's shared between multiple engines / generators) for a few reasons: Provides redundancy in case of an actual failure (not just low batteries) and it keeps the voltage dip from cranking away from the electronics (a big benefit IMO).

In the case of having 2x G27 for generator start, I'd probably combine those into 1 bank (and maybe swap to 2x G31). Use that bank for all engine and generator starting and have them wired so each can be switched to the house bank for starting as a backup.

 

[FF]

With a need for 2 batts to use for starting , I would still split them with a rotary switch.

The hassle comes from 2 batts wired in parallel , if one fails it usually will kill the other batt,so the reserve batt concept is defeated.

Just be sure to use stating rotary switches that can pass big amps and has an alt field cut off to save the alt if someone goofs with the engine operating.

 

[catalinajack]

With a very large house bank, yes, starting power is nearly assured as even very low batteries will have enough.

However, I still like separate starting batteries (at least 1 even if it's shared between multiple engines / generators) for a few reasons: Provides redundancy in case of an actual failure (not just low batteries) and it keeps the voltage dip from cranking away from the electronics (a big benefit IMO).

In the case of having 2x G27 for generator start, I'd probably combine those into 1 bank (and maybe swap to 2x G31). Use that bank for all engine and generator starting and have them wired so each can be switched to the house bank for starting as a backup.

My two G27s for starting the generators are already wired together. As fas as wiring them to be startimg batteries for my Lehmans and generators that is exactly what I choose not to do. Lots more additional wirimg for no added benefit. My large house bank will start the Lehmans just fine even if much depleted. As I said in an earlier post, in the unlikely event that my house bank is depleyed to uselessness, I can jump start using the generator starting batteries or start the generator and charge the house bank for a bit. Keeps the overall wiring much simpler with no loss in utility. There's no right or wrong answer here, just personal preference.

 

[Chuck16]

How to test?

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.

My GB42 (twin Lehman) has the same relay(s)? 3 on/off switches on the relay box. Two 8D on left bank and two 8D on right bank plus a 4D to start the Gen. The right bank had a battery failure. I can start the left engine fine. The right engine will barely turn over. No combination of switches seems to help. I can use jumpers cables however to start the right engine from the left bank with the failed batteries. Is there a way to test the operation of that relay?

 

[Gemini]

Thanks great help