Lithium Jump Starters

[Jfdodge]

Hi everyone,



On my Catalina 36 MK II (1999) I have a house bank comprised of two 4d lead-acid 12v batteries in parallel. I do not have a separate starter battery. There’s 360 watts of solar controlled with an MPPT controller and I have a Xantrex battery monitor keeping watch over all. I use my two 4d batteries for engine starting and for all house loads—leaving the selector switch on BOTH always.



Of course, even though it has never happened, I’m somewhat concerned that someday I’ll run out of juice to start my diesel. I sail on Lake Huron and each summer I spend a month cruising around in Canadian waters. Sometimes I’ll even spend a week anchored at the same spot, but with all LEDs, solar, and careful attention to the battery monitor I’ve never gotten into trouble...(i.e.) all batteries dead.


Nevertheless, for years I’ve considered putting in a separate starter battery and I’m aware of how that should all be configured, but given that I’ve never been dead in the water and that I love keeping things simple, I’ve another idea that I’d like to ask the forum about for your collective two cents.



What I’d like to do is simply reconfigure my 1-2-Both-Off switch so that the #1 position effectively becomes the Both location and the #2 position goes to a set of “Remote Battery Jumper Terminals” –you know—the kind Frankenstein has on the sides of his neck. They would be installed near the battery switch and then, in the unlikely event that I run out of juice from my 4ds located on the #1 position, I would simply switch to the #2 position which connects to my “Remote Battery Jumper Terminals”, clamp on to those posts with the alligator clamps from my 12-Volt Portable Lithium Jump Starter that I bought for 100 bucks and fire up the engine.


I presently have the Weego version of these devices and according to the specs, it can jump start a 35hp diesel without even blinking.



For me, these are the advantages:

1. This is as simple as it gets. No separate starter battery and all of the complications that entails.
   
2. I continue to never need to think about or mess with that switch because it’ll always be on #1 unless in an extreme emergency.
3. Both my 4ds become, in effect, one battery that is always charged from shore, solar, and alternator equally. This improves long term health of the battery bank.
4. And with a back-up Lithium Jump Starter, I’m covered in case something occurs that has never occurred before with my use of the boat on Lake Huron.

So that’s what I’m thinking.


Am I missing something here? Am I gonna bust my diodes, or fry my regulator, trash my 4ds, or is this simply not going to work for some reason.


Any thoughts out there?



Bueller...Bueller....

[wholybee]

I keep one on board. My primary use for it is as a power source for inflating my dinghy. But it will easily start the engine.

The main caution is that it only works while charged, and leaving it on the charger 24/7 will quickly ruin it. So it might not always be as available as you hope. One time a buddy boat needed a jump start, and at 50% charge my lithium jump pack couldn't do it. Even though at a full charge it will start a large 8 cylinder cummins.

I probably wouldn't bother with the switch and posts. During a jump start, you want as much power as you can get, and that will be from attaching directly to the battery.

[Jfdodge]

Hi Warren,


Thanks for your response. I didn't know that leaving a jump charger plugged in (charging) all the time could ruin them. Thanks for that. The reason why I'm thinking about having separate terminal posts is that I'm under the impression (perhaps false) that hooking up to my battery bank will immediately start to draw down the power of the jump starter--perhaps lessening its ability to crank the engine because the 4ds are in the way.


That's one of my questions that I don't know the answer to.


Regards,


John

[Mal Reynolds]

You are not missing anything. A portable jump starter is a fine substitute with a few caveats:
You have to keep it dry.
You have to keep it charged. But, Do not leave it connected to ships systems. Do not leave it charging all the time. This means you need to check it and top it up every month or quarter.

I assume you have an effective battery monitor on your house bank. Set it up to give you a low voltage alarm & test it.

Also, I would consider a 12v/12v power conditioner for your electronics as voltage gets pulled down when engine starting or using the windlass.

I've done this and its fine except you have to keep the jump starter maintenance in mind. One final thing is the Lithium chemistry is not LiFePO4, so be careful when charging.

[Kettlewell]

The situation I want to avoid is waking up at 0200 dragging toward shore and the engine won't start, so rather than rummaging around looking for the jump starter battery and then having to remember how to hook it up, etc. I can instantly turn the battery switch to an emergency position and just go. Yes, that situation is rare, but it does happen. In my case, I have a dedicated start battery that is always topped up via a trickle charging device from the house bank that handles all the major loads and gets all the charging inputs. But, in an emergency I can switch to the house bank and start in seconds. OTOH, this hasn't happened to mean in decades, because I tend to keep a pretty close eye on things.

[Shanachie]

This could be a loaded question, but what is the fire risk from one of these inexpensive jump-start units?


Same type of lithium battery goes goes into boats, or the cheap kind that occasionally catches fire? Are the units made of cheap metals prone to corrosion?


I used to carry one on board, and then had second thoughts and decided to rely on my TowboatUS card to solve any problems. I'm still not sure whether I was overreacting.

[Kettlewell]

This could be a loaded question, but what is the fire risk from one of these inexpensive jump-start units?

I think it is minimal when they are not on the charger, but when charging I like to keep an eye on them.

[Jfdodge]

Hi everyone again,


I've been doing some research on my own this weekend and I've determined that my idea using a jump starter hooked to a separate (from the house batteries) set of terminals might be a really bad idea. The problem is that at instant I fire the engine my alternator is going to start cranking out energy. Where is that going to go?


Perhaps it'll go back to the jump starter...not sure about that...but in any case, when I switch over from the new terminals to the house bank that energy will definitely have no place to go for an instant. I don't know about this stuff. Can someone explain it to me?


Thanks

[wholybee]

Originally Posted by Shanachie

This could be a loaded question, but what is the fire risk from one of these inexpensive jump-start units?


Same type of lithium battery goes goes into boats, or the cheap kind that occasionally catches fire? Are the units made of cheap metals prone to corrosion?


I used to carry one on board, and then had second thoughts and decided to rely on my TowboatUS card to solve any problems. I'm still not sure whether I was overreacting.

The battery in these jump start units is not the same LFP battery as is installed on a boat for it's house bank. It is the type that is in a cell phone, and boats have sunk and people have died from boat fires originating form a cell phone.

The risk is minimal while not charging. They also sell small fireproof bags.

[wholybee]

Originally Posted by Jfdodge

Hi everyone again,


I've been doing some research on my own this weekend and I've determined that my idea using a jump starter hooked to a separate (from the house batteries) set of terminals might be a really bad idea. The problem is that at instant I fire the engine my alternator is going to start cranking out energy. Where is that going to go?


Perhaps it'll go back to the jump starter...not sure about that...but in any case, when I switch over from the new terminals to the house bank that energy will definitely have no place to go for an instant. I don't know about this stuff. Can someone explain it to me?


Thanks

The alternator generators voltage. From that voltage, current will flow, up to the rating of the alternator. I don't see any problem if there is "no place" for that current to go. It will simply be a voltage with no current. The problem occurs when there is current flowing, and then you abruptly stop it. For example, by flipping a switch. Almost all modern battery switches are make before break, meaning that they never disconnect the alternator. For that split second while you are moving the switch, the two batteries are paralleled together.

If you are concerned, instead of an A/B switch, simply connect the posts to the starting battery, so they are in parallel. Add an on/off switch so you don't have an exposed 12V terminal when not in use

[donradcliffe]

The current setup has advantages of easily isolating one of your 4d batteries should it develop a shorted cell.

Charge your jumpstart device before you go out sailing for a month, and it should work fine to start your small engine.

If you have solar, just shut off the loads and wait for a few hours of daylight and you should be able to start your engine. All a start takes is one or two amp hours.

With solar and wind, I never had a dedicated starting battery for 15 years. The one time that one of the house batteries had a short, there was plenty of juice left in the other battery to start the engine at 0300.

[carlos1w]

Not on a boat, but I keep a small one I bought on amazon for about $50 (US). Never recharged it and it still has 3 out of 4 bars and restarted my Toyota RAV4 without a problem after my battery died. (after using it I re-charge it of course even though it still has 3 bars)

So keep it in sealed ziplock with some silica gel and recharge it every time you use it or once per few months.

[diverd]

I have one of these on both my boats, both my cars. I bought good ones from noko and bought the large one at £250 each. I have used them many times, mostly to test equipment, or to start other folks boats. I check the charge regularly but ad hoc, they dont appear to lose charge though. I am comfortable that in an emergency it would start either boats engine easily, and the terminals to attach it to are easily reached. I have a NASA battery monitor in cabin and at the helm, so its not for routine issues, more for the unexpected problems. Its literally a tool in the box

[Fintry]

Except for phones and computer devices that can easily be thrown overboard, I would not have an LiIon battery on board. Fire on a boat is the only emergency that potentially can kill the whole crew.


Except for the size of the battery, I'm not sure why this would be better than simply installing a flooded or gel battery as the engine starter. You also use a much smaller LiFePO4 battery, but it would be much more expensive.


Jim

[Kettlewell]

Typically, one hooks up a jump starter to the positive post on the battery and the negative ground. I would suggest you could just use the portable jump starter like that. Chances are the situations where you will need it will be very rare as long as you are monitoring things. It shouldn't take much juice to jump start any engine, and unless your battery bank is totally fubar it will just need a tiny boost to turn over the engine. Don't leave it connected full time. Just keep it portable and charge it once in awhile. One reason I like to have a dedicated start battery is so that there are no voltage fluctuations on my electronics running off of the house bank.