Lithium Jump Starters

[Rohan]

I also have a portable jump starter I got from Costco, and I have tested it when my batteries got too low to start the engine. It does work. It supposedly needs at least 75% charge to work. I leave it plugged into a shore power outlet, and I'm infrequently on shore power, but often enough to top it off once in awhile.

I think people are really exaggerating the danger of fire. I have never once had my laptop, cell phone, or lithium batteries on the boat catch on fire. Nor has anyone else I know.

I also don't see the point of creating a new place to jump your boat from. It's an event that should happen infrequently enough that you can just hook it to the batteries directly. Still use a voltmeter though - mine came with clamps but I had to adjust them just a bit before I finally saw the voltmeter jump up.

Anyway, I'll get to the point - if you are concerned about this issue, why leave your battery bank selector on "both"? Why not just one or the other? That way you never need to worry about accidentally draining both banks.

[GordMay]

Originally Posted by Jfdodge

... 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?
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

An alternator, running under no load, generates voltages, proportional to RPM, but, without any current [open circuit]. No harm - no foul.
However, if you disconnect the load, from an already running [& charging] alternator, you can damage it [back emf].

[clakiep]

In a emergency you can use your two batteries in series, for a short burst if the bateries are really low. But carefull not to frie your starter motor. With a wrench and a jumpcable easy to do.

Capt. Claus

[Coltrek]

I did the same on my C&C 39 as far as the battery situation, but just kept a Genius 70 lithium jumper in a drawer. Never needed it, but did loan it to others. I would never keep it hooked up. Also handy as a light or phone charger. Just need to check it occasionally and make sure it is charged, they don't like being completely discharged, forgot it on the boat one winter, and that was the end of that one.

[jen1722terry]

Question for those who are more electronically adept than we:

We now carry a jump starter and have removed our old starter battery. Should the system require a jump, can we just connect the jump starter to the old starter battery cables with the main switch set to "ALL"? I ask for our two AGM house batteries are more difficult to access than the old starter battery location.

Thanks in advance and cheers to all.

[Coltrek]

That is a good question, and altho I am not answering it, I can recall Jumping cars with stone dead batteries, and having to let it sit with the car doing the jumping, idle at a high rpm for several minutes, as it seemed the dead battery was sucking up all the initial voltage.

[nrx500]

I had what you have. After two days of sailing from NYC south, I lost the autopilot, LORAN, bilge pump, everything. And the diesel wouldn't start. Turns out the refrigerator drained the batteries. On the next boat I installed a small Blue Sea m-ACR between the dedicated starter battery and the house bank. The starter and house bank are linked until the house bank voltage drops below the starter battery. Then the m-ACR separates the starter from the house bank. Kill the house bank and you can still start the diesel. By the way, on the first boat I carried a spare car battery. I threw it in the sink and ran cables to the starter. Once I had the diesel running, I shut down the DC panel and motored the 100 miles to Norfolk.

[moseriw]

Maybe I can give you a few inputs as I had similar problems using simple truck FLA batteries.
Nowadays the batteries are splitted into several types.


Starter batteries are optimized for cold start with around 1000-1200Ah but have to be recharged immediadely to their optimal voltage, say 12,6 V. (You do not believe it? Me too, but ask wikipedia) Using them as house batteries and discharging them down to SOC <=50% = 11,8V will ruin them on the longer run. Give them 3-5 years and they are done..

A solution is AGM with dedicated "house" batteries. they are called "deep cycle" something.

Next problem:
I have Trojan FLA's that can be "watered." but the problem is that they need to be refilled every 2-3 months and will be without enough water every winter. (Trojan said it is not a issue and the batteries are designed for this situation) Disconnecting them from the panels is no option as the bilgepumps have to stay connected - for security reasons.

LiFePo4: One can discharge them until they give up at around 5% but should not be discharged below 20% which gives them a lot more capacity with the same said Amps-max.

BUT: they can not be charged with a simple alternator as they suck the max of current(Amps) out of it and will overheat and ruin it. Solution is a good old starter battery and B2B Chargers for the LiFePo4 or maybe a special A2B-Charger that controls the Alternator and limits the Amps.

Hope this helps.