House battery or start battery to use for genset starting?

Chris Patterson · Oct 15, 2015

Funny, I was working on a Northern Lights yesterday. And myself and another yard mechanic/contractor were discussing this. I would vote the house bank. Save the engine battery for cranking the main engine period. If by any chance you kill the cranking battery, the generator should maybe start from the house and recharge the crank. And if the house is too low to crank the generator, then the crank should light up the main engine so it can charge the house to fire the generator.

(I hope that's not confusing, my proofread seems muddled.....my English major wife would kill me if she read this)..

kenny · Oct 15, 2015

i have a northern lights 5KW ,i use the engine start batt. to start the gen i first start the engine and has plenty of power to start the gen. i have a hunter 410 , make sure it has a load on the gen.

Rich Stidger · Oct 15, 2015

I use the house bank. I also have switching to connect the start battery to start the generator, and the house batteries to start the engine. In short I can start either the generator or the engine from either set of batteries. But my normal config is to start the generator from the house and the engine from the start. My generator (Westerbeke), and probably yours too, has a 12V output to charge a dedicated battery if you wish, or its output just combines with you other generation.

windward54 · Oct 15, 2015

On our boat, I installed a second starter battery. I installed a battery large enough to start the boat's engine. That way I always had a backup to start the engine if needed.

seadaddler · Oct 15, 2015

I have been using a start battery for the engine
and Gen and also have a switch over from the house to the start battery so either way I am good to go and I use a normal auto battery for the start battery and 4-6 volt for house and solar.
Nick

Gunni · Oct 15, 2015

I have the NexGen 5.5 also. Reliable genset. And like Rich can use either my house or engine battery because Beneteau wires up the disconnects that way. In my opinion the engine start battery should be there, ready, and never used until the Kimchi hits the fan and you need power to your aux starter, but your house bat is dead. So I would recommend a disconnect for each battery bank.

I also have a gen starter disconnect on the DC source so that I can render the generator unstartable. And I have an AC disconnect next to the generator to isolate it from the ship's AC system. I believe these are SOP installs.

Stu Jackson · Oct 15, 2015

Gunni and Rich are right. You really need to set up your electrical system so that either bank can start the engine or run LIMITED house loads in case one bank craps out. This can be done with a simple 1-2-B switch or multiple switches.
Like these:

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: http://c34.org/bbs/index.php/topic,6604.0.html

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

jlp0217 · Oct 15, 2015

I don't have a genset, but my thought is using the house battery to start the genset makes as little sense as having a true reserve battery not used for anything. Isn't that the ABYC recommendation? Starting the genset, just like starting the propulsion engine is a high amperage short time event, followed immediately by a recharge. Not a deep cycle application. A charged starting battery in good condition should be able to sit a month and still start the engine - just be sure all parasitic loads are on the house, not the start battery.
Just in case, carry jumper cables, or add a switch to be able to start from the house batteries, but seems to me they are much more likely to be discharged to the point they won't start the engine. I'm not sure how to know when the start battery is old enough to need replacing other than it won't start the engine, but when it gets there replace it.
I had an old start battery of unknown age, so for anything other than a day sail, I brought along my car's emergency starting battery. You know, the kind with built in charger, light and air compressor. I ended up having to use it on my trip to Alaska in 2014 when first my alternators, then starting battery failed. I replaced the starting battery with a cheap one from Costco in Juneau and wont worry about it again for 5 years or so.

Maine Sail · Oct 15, 2015

smokey73 said:
I'm installing a Nextgen 5.5 Kw Genset in my Hunter 40.5. Just about done with the installation and now have to decide which battery bank to use for starting the GENSET. Do I start the Genset from the House Bank or from the Engine Start Battery? Advantages/Disadvantages. Would it be better to get a separate small Generator Starting Battery? If so how would I keep it charged?

Right now I don't have a Off 1 2 Combine type battery switch. There is an On/Off for the House Bank and a separate On/Off for the Start Battery with a Blue Sea Battery Link ACR to handle charging the Start Battery.

Which battery do you use and why? Am I overthinking this one?

Thanks in advance

Really there is no right or wrong way here. If practicing good battery management (never letting the house bank dip below 12.0-12.1V during average house loads) then starting the gen off the house banks will work perfectly fine. A properly sized house bank for a 40 foot boat (400Ah plus) will have more cranking ability than a single starting battery even when it is at 50% DOD.

If you are not practicing good house bank management, meaning no well calibrated Ah counter, Smart Gauge or accurate voltage measurement, then starting of the start battery would generally be preferred.

If the choice comes down to adding more lead to the boat then I usually prefer to see this weight put into the house bank where it can actually do something other then sit there as a second bank (third bank in total) of dead lead or 98% unused weight. It will take less than .5Ah of battery capacity (often less than that) to start a gen set this means approx 99.5% of that weight is being carried around never being adequately put to good use.

If you use dedicated start and house banks the starting bank sees very little use from starting the engine so the usual approach would be to tag the genset onto the starting bank. On boats over 45' then perhaps a third bank could be feasible but we then often get into bow banks too so I still generally use the engine bank for gen set rather than having three banks of "dead lead" and one house bank where the capacity is actually used...

If you choose to use the start bank for starting both engine & generator you will want a way to:

Isolate HOUSE bank entirely
Isolate START bank entirely
Start and draw house loads from START bank
Start and draw house loads from HOUSE bank

In other words a three switch system where one ON/OFF is START, one ON/OFF is HOUSE and one ON/OFF is EMERGENCY PARALLEL. Emergency parallel needs to be correctly wired to the load side of the switches and it is most often incorrectly wired to the battery side....

capta · Oct 15, 2015

My house bank are deep cycle batteries, not really the preferential battery for engine cranking. Therefore I use the 4D engine start battery to crank the generator. As long as you have enough juice in both banks to start the gene, you really don't have to worry about the juice to start the much bigger ME, right?
With the solar and windgen charging both banks pretty much 24/7, I can't ever see not having enough juice to start a small craft generator. Now if we were talking about 10,000kw, that would be a much different story.

Benny17441 · Oct 16, 2015

I agree that either way is OK with no definite advantage or disadvantage for either choice. I just endorse the idea that the electrical 12V system should be wired so either battery bank can be used to start the engine. Do not endorse at all the addition of a small dedicated battery for the genset; besides its cost it would just add weight, occupy space and complicate the wiring layout for recharging.

Ron20324 · Oct 18, 2015

smokey73 said:
... I plan on the changes to the battery systems to have the three switches Maine mentioned. That is in the works but I have to figure where to locate the Emergency Parallel switch. Its about a 15 foot cable run between the two switches I now have. ...

My B323 three switches for 3 batteries are next to each other. I wired a heavy cable across the three switch's load side. In effect, this cable becomes a +12-volt buss, with all loads/sources wired off of it. This way you select any combination you want to use or charge, and you parallel 2 or 3 batteries just by turning them "on".