20 hp yamaha I want to disconnect charging system

[tryn2lrn]

Hello, I have a 20hp yamaha outboard that I do not want to charge the battery that starts it. Can I just disconnect the rectifier regulator wires? I assume that charging is back through the high current leads run for starting and not separate wires. I want to use a LiFePO4 battery instead of the SLA. I was told that the charging from the outboard motor will ruin it.

[zenoahphobic]

I am not all that convinced about direct replacement Li for Pb in motorcycles, which are common, and would suit for cranking your outboard.
Two things are a problem, Li need 15volts and when full need to switch off with no trickle charge. Get this wrong your battery dies, no recovery.
Now what I have seen done is the battery comes with internal circuitry. To get full charge 15volts appears available from flywheel magnetos. Not so from alternator charging: they are set to a lower voltage, 13.8 to 14.5 volts: the Li seemingly will never fully charge. This might be OK if you have a large battery and small alternator. You still need to cut off float charge.
The third worry is the Li although has more charge cannot go below a point They will output well but then Dead. Easy to make very expensive mistakes!

[99yam40]

why would you even try to use them?
Many years of use out of normal batteries

[boscoe99]

If the Lithium battery has a BMS that is rated for starting then all you need to do is to replace the lead acid battery with the starting lithium battery.

Before you do that however I would verify that the voltage output from your F20 (my guess is that it is a four stroke model) alternator is less than the maximum voltage specified for the lithium battery.

[boscoe99]

why would you even try to use them?
Many years of use out of normal batteries

Weight and the fact that they will output power for long periods of time and still be able to start a motor.

[zenoahphobic]

Weight and the fact that they will output power for long periods of time and still be able to start a motor.

Unlike Pb, Li actually go DOWN in internal resistance, the more you crank, the crank becomes faster.
Lifeo..weight is about 1/3 for the same useable capacity.

[tryn2lrn]

Yeah, a few things I didn't mention. The actual full charging will be from my MinnKota charger, yes the new one for LiFePO4. I use my outboard to get from spot to spot, then *****ing motor, so the charging of the battery is really not dependent on the Yamaha. I just don't want the output of the yamaha to ruin the battery. Full charge is done at home, like the *****ing only batteries. I don't think this is an issue as my BMS on the batteries will prevent over and under charging issues etc. The BMS is set for 100A so I don't think my F20 will draw more than that to start(I hope not or i'm done). Weight is the big issue for me as I am getting older and my back is not so great anymore. Even using group 24 size they are freaking heavy and trying to get them up to shoulder height and then stuffing them in and under the drip well in the trays is well a painful experience. The Lifepo are less than half the weight, they have 33% more AH, and they way I use them should last me 3x longer. Think I am just going to give it a try. I will see If my current clamp and meter will capture the starting current, I kind of doubt it. Anyone know what the current draw is the start the F20 4 stroke?

[99yam40]

try your clamp on ammeter to see if it will give you some type of reading. I think you will be surprised how much starter motors draw.
even T&T motors suck a lot of amps for their size.

[zenoahphobic]

try your clamp on ammeter to see if it will give you some type of reading. I think you will be surprised how much starter motors draw.
even T&T motors suck a lot of amps for their size.

Yeah back ache, I feel you!
You can use your charging from your outboard by using DC to DC charger with the LiFePO4 charging map. Eg CTEC 250. They tend to wait awhile after engine starts before switching to battery, and similarly stay on for awhile before disconnecting. This is to stop repetitive On Off switching (but very annoying when one suspects a fault) They also accomodate solar input if you have the deck space (or windmill and any generator)
A disadvantage is that the charging cycle starts all over again if engine is turned off and on again. But I think these units are smart enough to realise when the battery is already full.
Remember high current discharging reduces the life of these batteries (others also).
The technology used for these battery setups is amply discussed in camping and outdoor forums.