Battery Bank (2 x 6vdc) for Starting

[silverp40]

It may be that this was a question previously asked but I could not find it:

Is anyone using a pair of 6v (golf cart wet cells) batteries wired in series as a starter battery bank?

Reason for my ask is that when combined during charging, the starter (which is gel) and house batteries (4 X 6v wet cells) do not match propery voltage wise - gels cells have different voltage requirements for charging than wet cells so they get damaged in teh long run. I also do not want to use an echo type regulator for the gel batt.

Any help is much appreciated

Chers to all!!!

[onestepcsy37]

been using trojan t105 golf cart batteries to start my perkins 4-108 for the past five years. don't have a so called 'starting' type battery.

[kb79]

starter batteries should supply a large amount of current for a short period of time (cold cranking amps).

dunno what the specs are on your proposed batteries, but that's what i'd check.

[btrayfors]

What, exactly, are you wanting to do?

If you just want to use all flooded batteries, toss the gel and get a proper (flooded) starting battery. Then, bite the bullet and use an EchoCharge or DuoCharge to maintain that battery.

Is your problem with the charging? You're right, it's not a great idea to combine gels and flooded batteries, because the voltages used for flooded batteries can exceed safe limits for the gels. On the other hand, it'll work for awhile, so you could just go ahead and do most anything until the gel dies, then get a flooded starting battery.

Bill

[silverp40]

Hi Bill

By using two 6v batts for starting, we would have a somewhat larger starting bank but also a bank similar to the two others (4x6v house use) for emergency use. Plus the 6v batts have capability of deep discharging than say a group 27 and are easy to find (and purchase).

The starter gel cell batt is in a location where regular maintenance is difficult, hence gel. THerefore, I am thinking of relocating it to somewhere else, where it is easy to maintain. This new location could accomodate two 6v batts so I am thinking why not....We do have the charging capability for the extra 100 amps or so of capacity.

Thanks all for all the input
Cheers
Ovi

[keyspc]

probaly depends on the engine.
i had a 2cyl yanmar that ran on veggie fuel(high compression low rpm). the golf carts would quite spin it fast enough, long enough but not fast enough for quick start.
ended up puting the vetus back in(low compression high rpm) and it starts like its been kicked.

[silverp40]

Originally Posted by keyspc

probaly depends on the engine.
i had a 2cyl yanmar that ran on veggie fuel(high compression low rpm). the golf carts would quite spin it fast enough, long enough but not fast enough for quick start.
ended up puting the vetus back in(low compression high rpm) and it starts like its been kicked.

Interesting!
Did you by any chance measure the voltage on the starter batts DURING cranking? A voltage of low 11s or even lower means the starter batteries' condition could be so-so, sulfated or otherwise.

The Vetus starter (with it's low compression ) might not need such sustained, high top end current as the Yanmar to get the flywheel spinning...

Ovi

[svcattales]

I use 6 volt golf cart batteries for starting both engines and have effectively eliminated a separate engine start battery.

When I cruised my monohull for 8 years, I started with a dedicated starting battery. After replacing it every year despite little use, I realized the charging demanded by housebank was cooking the engine battery. When I paralleled the start battery with the house bank, the problem disappeared.

Now I have one large bank on the cat that serves as housebank and engine-start for both engines. After 5 years of cruising this has worked well. If I have battery problems, I can isolate 2 golf carts on port side from the 4 golf carts on starboard side. I know this defies conventional wisdom about having a dedicated starting battery, but it keeps all batteries charging & discharging in unison and I think it keeps them healthy. Also, I keep a close eye on the voltmeter so I've never had a problem starting the motors.

[Ike]

Starting batteries and house batteries are constructed differently. Starting batteries have thin plates and are designed to release large amounts of current rapidly because starters require large amounts of current to crank over the engine. They do not like to be deeply discharged. After releasing about 20% of their capacity they need to be recharged. if you go much below 80% they are dead dead and very hard to recover. They like to be charged on a regular basis. I never let a starting battery stand without charging for more than a week. In other words they need a maintenace charge. Using them as a deep cycle will kill them very quickly.

Deep cycle (house batteries) have thick heavy plates designed to release amps slowly. they can be discharged down to about 20% of their capacity. But they can be recharged repeatedly from 20% to 100% with no damage to the battery. Using a deep cycle battery as a starting battery repeatedly can warp the plates because the requirement for releaseing large amounts of current can overheat the plates. Using them occasionally to start an engine will not damage them. On a sailboat where you only start the engine to leave or enter port will probably not casue damage.

Mixing battery types is not advisable. Mixing different sizes (capacity not physical size) is also not advisable especially if the batteries are parralled or in series as are deep cycle battiries. You not only get an imbalance in charge between batteries, you even get an imbalance between the cells in an individual battery.

See: Batteries and chargers http://newboatbuilders.com/docs/Batt...ndChargers.pdf
and Does Size really matter http://newboatbuilders.com/docs/Battery_Size.pdf

[silverp40]

HI Ike

Thanks for the comments. I agree that deep cycle batteries will eventually damage if using them repeatedly as for starting, ie high current output. However, having 2x6v batteries will produce a 200 amp battery as opposed to a more standard 100 amp or so starter battery.

Since this is much larger capacity, almost double, what is your opinion on the damage created by using this bank to start a 55hp diesel?

Thanks
Ovi

[Ike]

Do you start it on a daily basis or is it just an auxiliary used for getting in and out of port? Those golf cart batteries can take a lot of punishment. How are you charging them?

[silverp40]

We don't need to run the diesel to charge the batts, therefore quite a bit less starts. We also sail a lot without motoring....

We have a 400 a solar array and 2 wind gens so all our electrical needs are pretty much covered. The Pvs are enough to keep the batts charged up without the wind generators.

[Ike]

Sounds like a good arrangement

[Pete7]

I am just wondering if a 200 amp battery bank is over the top for a 55hp diesel. My little Peugeot has a 50hp 1.5L engine and starts with a battery I could span with my hand. Okay if it fails to start my car wont' drift onto rocks but do you really need such a big engine start bank? Afterall there is a cost involved that may not be required.

Pete

[svcambria]

Now I have one large bank on the cat that serves as housebank and engine-start for both engines. After 5 years of cruising this has worked well. If I have battery problems, I can isolate 2 golf carts on port side from the 4 golf carts on starboard side. I know this defies conventional wisdom about having a dedicated starting battery, but it keeps all batteries charging & discharging in unison and I think it keeps them healthy. Also, I keep a close eye on the voltmeter so I've never had a problem starting the motors.

Voila! Someone else who does that! Same here - except on a monohull with one engine. The extra 200 amp hours are really welcome in the house bank, the batteries are all used evenly and recharged evenly with fewer deep discharges and less cycling. I also have a 5 HP Kubota DC generator with hand crank capability, but never had to use it "in extremis". Eight years and counting - so far so good...
For those who are truly worried, perhaps a small portable generator to boot things up if your batteries get too low?

Michael