Do I really need a separate starter battery

[Stewie12]

Well said Chris. Let common sense prevail

[capn_billl]

Originally Posted by Chris Cringle

If, God forbid, you lose your house bank charge at about sunset, just as an onshore gale rolls in, you will have to wait until at least 1000 hours the next morning to begin to "wait a couple of hours for the solar panels to charge the batteries". Yeah, you can save about one cubic foot of space and a few feet of heavy wire, but......you bet your boat.

Yeah this.

I woke up one night to an anchor alarm, turned on lights, no lights. Tried to start engine, no start.

Fortunately I always carry a 20 ft coil of 0 gauge wire with terminal ends.

A quick jumper to generator battery (completely standalone), and I'm back up. Engine starts, drive to re anchor, lights come on when I start generator, and find fried diodes in alternator, and bad battery in house bank that drained the rest.

I always carry a spare battery, and tie it to engine starter occasionally to test it, and re top off, then back in the locker. it's $120 peace of mind.

I also keep a spare alternator, and usually a starter. (right now just a spare solenoid, but the starters are brand new).

[Zzmeyer]

Originally Posted by Chris Cringle

If, God forbid, you lose your house bank charge at about sunset, just as an onshore gale rolls in, you will have to wait until at least 1000 hours the next morning to begin to "wait a couple of hours for the solar panels to charge the batteries". Yeah, you can save about one cubic foot of space and a few feet of heavy wire, but......you bet your boat.

Given I have 900 amps of lithium, I would need to fail to check battery status for three days or so, ignore the low SOC alarm, have a failed solar set up (no chance of zero power at sunset otherwise), failed to check the weather, failed to properly set the anchor and forgot how to sail. I'm looking to mitigate risk, not eliminate it. There are so many more likely scenarios than this one to prepare for. If mixing a flooded starting battery with lithium house were as easy as a couple wires I'd consider it.

[Adelie]

It is a calculated risk.
I personally would take that risk.

There are 3 cheap options I can see for emergency starting:

A. Lithium Jumpstart pack
B. Capacitor Jump pack. If there is any juice coming out of batteries pack will harvest enough over several minute to crank the engine. https://www.autowit.com/
C. DIY crank pack using a little hand cranked generator and some supercapacitors.

If you go with a small battery for starting and are trying to figure out simple recharging. 10W solar panel on top of the dodger and a small PWM controller. Unless you have an oversized engine that has problems starting total energy use will be under 1Ahr per attempt. Probably under 0.5Ahr. The 10W panel will give you 3-5 starts per day.

[Bowdrie]

Originally Posted by skenn_ie

It is only a matter of time before SOMETHING discharges one bank.

As a NA/ME friend told me, (tongue in cheek,) "Be sure and have lots of batteries, that way you can go longer before they all go bad/dead".

[Dieseldude]

A separate starting battery with an isolater makes the most sense for safety and convenience. Unless a very careful watch is kept to avoid draining a single battery with the house load, the battery will at some time discharge beyond its capacity to start the engine. The could be dangerous or at least very inconvenient. With no means to start the engine and no shore power or auxiliary generator to charge the battery, you could be in a very bad situation. Even with alternate power available, it takes time that you might not have to charge a dead battery. Even those portable starting batteries are not 100% reliable. It can self discharge over time, or after using, it can be forgotten to recharge.

[more]

Originally Posted by mvweebles

The reason lithium are not recommended for starter is due to high amp draw that is beyond the BMS setting of a single lithium battery. Parallel several lithium together and you can build-up delivery of required current. Also, voltage drop across lithium is much less than FLA so electronics should be fine.
Good luck
Peter

Lithium batteries don't need BMS. in fleet 2 my charter boat have Winston cell 200ah i only put 5A balancer on the battery. no problem now 3 year in work.

[Don C L]

Some years back, buddy boating with a friend, he had just one battery bank and woke up to a dead battery. I had one deep cycle battery for my little boat (and with an outboard, no need for it for starting) so I unhooked it and we hoisted it over to him. He would have been pretty stuck without it, not so much to sail OUT of the anchorage, but to get back into the marina we were headed for. Yes for 2 banks from me.

[goboatingnow]

Originally Posted by Don C L

Some years back, buddy boating with a friend, he had just one battery bank and woke up to a dead battery. I had one deep cycle battery for my little boat (and with an outboard, no need for it for starting) so I unhooked it and we hoisted it over to him. He would have been pretty stuck without it, not so much to sail OUT of the anchorage, but to get back into the marina wue were headed for. Yes for 2 banks from me.

I have two battery monitors. How does anyone “ wake up “ to a dead battery these days. Answer cause they are incompent or couldn’t be bothered to install a monitor.

In the last 20 , yes twenty years , I’ve never had an unexpected battery failure or unexpected dead battery situation. I can see batteries slowly failing etc. But not the “ wake up “ to a dead battery.

That’s not a failure sceanario that’s just incompetence quite frankly

These days a separate lithium jump start option is widely available so systems that don’t want a permanent starter battery can easily carry a backup. I do agree an alternative method should always be available but that does not excuse ending up with dead batteries

[goboatingnow]

Originally Posted by Dieseldude

A separate starting battery with an isolater makes the most sense for safety and convenience. Unless a very careful watch is kept to avoid draining a single battery with the house load, the battery will at some time discharge beyond its capacity to start the engine. The could be dangerous or at least very inconvenient. With no means to start the engine and no shore power or auxiliary generator to charge the battery, you could be in a very bad situation. Even with alternate power available, it takes time that you might not have to charge a dead battery. Even those portable starting batteries are not 100% reliable. It can self discharge over time, or after using, it can be forgotten to recharge.

Everything can fail. In my experience the starter goes bad first , because it’s not actively monitored and gets “ forgotten “

The lithium starters are excellent , can be recharged in some cases from USB. ( your “ dead” house battery can still recharge it. Etc.

Let’s not postulate all sorts of edge cases. The basic idea is to have an alternative , that can take many forms other then the traditional hardeaired in starter battery.

[valhalla360]

Originally Posted by Zzmeyer

I started sailing when a sailboat had one battery. You woke up in the morning and the engine wouldn't start. Someone figured out to separate the engine start battery from the house bank. My new boat will have 900 amps (12.8 volts) lithium and 1200 watts solar with a Victron battery monitoring system. So why do I still need a separate starter battery? It is very unlikely I'll ever run the house bank down both because of its size and monitoring capabilities and if I do, wait a couple hours for the solar to recharge. While redundancy is always nice, the complexity of multiple battery types and their charging requirements seems to offset the advantage. It would give me more space, less weight and less complexity if I just skipped the starter battery. Help me with my idiocy.

I think this is old school thought in the power boat world. A big engine (particularly diesel) takes a lot of amps to turn over. If you only had 4- 6v golf cart batteries and they were a long way from the starter, they might not generate enough amps at the starter to turn over the engine. 1 or 2 starter batteries adjacent to the engine solved the need to generate lows of amps.

If your battery bank can provide 900amps to start a small sailboat engine as you indicate, I don't see it being an issue starting a 20-40hp engine.

I am presuming your monitoring system will cut house loads before the battery bank goes dead, so you have enough to start the engine.

We did that on our catamaran but with outboard power, I could pull start if the batteries died.

Some of this discussion reminds me of the old requirement for transatlantic planes to have 4 engines and now they refuse to fly on a twin engine jet...even though the modern twin engine jets are more reliable than the older 4 engine planes.

[malbert73]

Originally Posted by Dockhead

To my mind, this is clearly Best Practice.

I especially advocate jumper cables instead of some kind of interconnection switch for emergency jumping. Nothing to fail or go wrong or to be set incorrectly. "A B Both" switches are from the devil.

Originally Posted by Dockhead

That's it.

You could carry one of those emergency starting packs (or are they fire hazards?).

But do you want to faff with that at o dark hundred when your anchor is dragging and you can't start the engine?

I go, personally, with completely separated engine start battery and charging system, separate alternator, not touching house system in any way. Not even same voltage. Necessary? No. Prudent? You bet your hind parts.

Hi DH- your two consecutive posts made me chuckle (reverse order above).
You don’t want to mess with a jump start pack in middle of the night when your anchor is dragging but want to do same with jumper cables?

What’s wrong with a well maintained switch? My house and starting battery switches allow for starting engine with both- I even have the number sequences written out on a card so when SHTF I don’t forget how to switch things (including bypassing the fuse for house bank)

[Davidla]

I live the Lithium house bank situation every day.
I have a 100amp AGM start battery. I have two victron superpack 200amp house batteries wired in parallel. My start battery is connected directly to the engine starter and to a Victron DC- DC charger. Which then connects and charges the house bank three minutes (configurable) after engine start. When the engine is not running the DC-DC charger is off.
The maximum current supplied by my house bank is 100 amps. It will not start my engine even if I wanted it to. Victron say it is safe to assume the maximum output for the superpack battery is 100 amps even wired in parallel and even though each has a maximum output of 100 amps.
My Universal 35hp engine probably needs 250-300amps for a very small time to start the engine and it can't get it from the housebank. If I try to start from the house bank the ignition key goes to the first detent and powers up the instruments and glow plugs. If I try for engine start the BMS shuts the party down and disconnects itself.

A drop in Lithium battery with integrated BMS generally has much lower amp peak capacity than one with an external BMS. If you want to start a (yacht) diesel from a Lithium battery get an external BMS design.

How do I manage? I keep my starter battery in good condition and check the voltage regularly. I also carry a jump pack as a reserve. Note my jump pack is Lithium and I would not try to start the engine with it. I would connect it to the start battery for five to ten minutes to put some charge into the start battery and then try to crank the engine.

[Zzmeyer]

Originally Posted by Davidla

I live the Lithium house bank situation every day.
I have a 100amp AGM start battery. I have two victron superpack 200amp house batteries wired in parallel. My start battery is connected directly to the engine starter and to a Victron DC- DC charger. Which then connects and charges the house bank three minutes (configurable) after engine start. When the engine is not running the DC-DC charger is off.
The maximum current supplied by my house bank is 100 amps. It will not start my engine even if I wanted it to. Victron say it is safe to assume the maximum output for the superpack battery is 100 amps even wired in parallel and even though each has a maximum output of 100 amps.
My Universal 35hp engine probably needs 250-300amps for a very small time to start the engine and it can't get it from the housebank. If I try to start from the house bank the ignition key goes to the first detent and powers up the instruments and glow plugs. If I try for engine start the BMS shuts the party down and disconnects itself.

A drop in Lithium battery with integrated BMS generally has much lower amp peak capacity than one with an external BMS. If you want to start a (yacht) diesel from a Lithium battery get an external BMS design.

How do I manage? I keep my starter battery in good condition and check the voltage regularly. I also carry a jump pack as a reserve. Note my jump pack is Lithium and I would not try to start the engine with it. I would connect it to the start battery for five to ten minutes to put some charge into the start battery and then try to crank the engine.

Thanks so much. Very helpful. The only issue I have with this configuration, if I understand it, is that your alternator will only charge the lithium (through the start battery) at the rated dc-dc limit. I didn't mention in my original post that I also plan on a high output alternator. At what rate can your alternator charge the lithium with this configuration?

[Davidla]

Originally Posted by Zzmeyer

Thanks so much. Very helpful. The only issue I have with this configuration, if I understand it, is that your alternator will only charge the lithium (through the start battery) at the rated dc-dc limit. I didn't mention in my original post that I also plan on a high output alternator. At what rate can your alternator charge the lithium with this configuration?

I have the original 55 amp OEM alternator installed on my boat and cannot charge the Lithium batteries directly from it, it would burn out pretty quickly especially at engine idle. My DC-DC charger is only rated to 30amps but I only run my engine for about thirty mins each day most days manouevering (yacht). But I also have 400w of solar. The lowest I have ever seen my house batteries is 46% but this is only a six month old install. I carry a Honda 1000Eu as a backup power supply but have only used it to run the microwave oven using the power assist from my Victron 1600 inverter charger. When I do this amps out from the batteries are about 30-40 and the Honda is running at about half pace after the inrush current is finished.
Sorry more information than you needed.