Protecting lithium batteries from high voltage

[Spartanacus]

This new to me sailboat has double 9.9 Yamahas as propulsion. Batteries consist of 3 flooded batteries as house bank and no starter battery. The house starts the 9.9's and of course are charging the house.

I'm installing 660W of solar and 3 - 100A LiFePO4 house batteries to replace flooded and adding a small lithium starter battery.

Question is: what is the best way to throttle down the voltage coming from the 9.9 Yamahas to a max of 14.6V? Or is there a better way to isolate these outboards ... the output is a meager 6amps and will not be essential.

[wholybee]

Originally Posted by Spartanacus

This new to me sailboat has double 9.9 Yamahas as propulsion. Batteries consist of 3 flooded batteries as house bank and no starter battery. The house starts the 9.9's and of course are charging the house.

I'm installing 660W of solar and 3 - 100A LiFePO4 house batteries to replace flooded and adding a small lithium starter battery.

Question is: what is the best way to throttle down the voltage coming from the 9.9 Yamahas to a max of 14.6V? Or is there a better way to isolate these outboards ... the output is a meager 6amps and will not be essential.

I advise against a Lithium starter battery. In a starting application, Lead Acid is actually a better battery.

That fact makes your question easier to answer. Use a DCDC charger between the Lead acid battery and the LFP house bank.

[sailorboy1]

A 9.9 HP outboard hardy needs any starting battery. I use a $30 U1 lawn equipment battery. The 9.9 alternator is pretty small, but I have no idea what it can do for voltage. But if needed a DC - DC may be needed

[Nicholson58]

Last year we switched from Firefly AGM to lithium LiFePo. We chose Blue Heron for house and start banks. Hank George is the rep. He is extremely helpful and knowledgeable. He located links needed for updating all of our charging devices and supplied patch cords, adapters, special devices needed for proper installation. With Hank’s assistance all was completed in Trinidad over the course of about a week.

If you’ve not already bought your stuff, call Hank.

Blue Heron https://www.blueheronbattery.com/

hank@starboardlanding.com

My customized install replaced all lead batteries. Having a dedicated lithium start bank sized for my 180 amp starter eliminated a lot of special electrical devices. I leave it in parallel through existing switches with my house bank. This gives me over 700 AH at 24 volts.

The usual method to control over voltage from the engines is to equip the alternators with external charge regulators such as Balmar. This may not be possible on an outboard. If it’s possible to switch off the alternator after about 95% full charge this may be an option. Even with my Balmar I have a ‘disable’ switch for long distance motor-sailing.

I also wonder why you would need a start battery with 9.9? If you are close on the max current inrush to a starter maybe just parallel another Li battery to the house bank.

Here is a link to a site I found helpful

https://marinehowto.com/lifepo4-batteries-on-boats/

[hlev00]

I would expect that LiFePO4 house batteries could start your 9.9s without disconnect but you would want to verify the capacity.


However I believe you bigger problem is that the LFP batteries will toast your tiny little alternator on on the 9.9. You might be able to use a smallish DC-DC charger to charge from a flooded battery to the LFP and have the flooded battery charged by the 9.9. But to be small enough to protect your 9.9 alternator may not provide useful power for charging the LFP.

You could connect the solar via MPPT to either bank but likely more efficient to charge directly to the house. Keep a small lithium jump pack for emergencies should the flooded start battery get drained or fail.

[sailingharry]

An important consideration is that a battery's voltage is largely a function of the battery, not the charger. That is not entirely true, but mostly true and more so in your case. You have 12 amps of charging capacity at your disposal, and 300Ah of lithium. The battery will overwhelm the chargers.

The point I'm trying to make is that it doesn't really matter what setpoint your outboard alternators are set for, they will try valiantly to raise the voltage of the LFP without success.

This can become a problem only if your battery is 100% charged. And even then, since the solar will have throttled back at that point (because they have a set point and recognize the battery is fully charged), the only charging source will be that 12A. In all likelihood, your operating loads (fridge, chartplotter, autopilot, etc) will exceed the potential charging current.

It is possible for your alternators to eventually overcharge the LFP. But it will be an unusual scenario, and will take extensive motoring for it to happen. You could spend money and add complication to make this an impossible scenario. Or you can simply monitor the situation and in the unlikely event that battery voltage starts to creep up towards unacceptable, turn on a couple of cabin fans or crank the stereo (in other words, add a load greater than your alternator output)

[Nicholson58]

Originally Posted by hlev00

I would expect that LiFePO4 house batteries could start your 9.9s without disconnect but you would want to verify the capacity.


However I believe you bigger problem is that the LFP batteries will toast your tiny little alternator on on the 9.9. You might be able to use a smallish DC-DC charger to charge from a flooded battery to the LFP and have the flooded battery charged by the 9.9. But to be small enough to protect your 9.9 alternator may not provide useful power for charging the LFP.

You could connect the solar via MPPT to either bank but likely more efficient to charge directly to the house. Keep a small lithium jump pack for emergencies should the flooded start battery get drained or fail.

Good point on the teeny alternators. I toasted two before I limited the Balmar external regulator to 50%. Most alternators are not rated for continuous full load output. Even the case temperature sensor was not enough. The hot, burned component was the rotor. Are these on the OP’s motor typical outboard motor chargers?

[Spartanacus]

Not worried about starting an OB tho the battery manufacturer stresses they are the house bank and made different, not for starting.

BTW, there is a Lithium starter battery in my high compression 1300cc V twin motorcycle. On it's fifth or sixth year now, it spins the starter like it's a moped. (earthX)

Concern is with this unsophisticated charging system sending too much voltage to expensive lithium batteries. If it was an inboard with alternator then an adjustable regulator could solve the problem. Also too much voltage probably will shut down the solar side as it senses this voltage.

Maybe the 2 OB's and a start battery could be isolated ... never to see the house bank?

any thoughts?
good info out of you guys so far. Especially the informative links.

[wholybee]

Originally Posted by Spartanacus

Not worried about starting an OB tho the battery manufacturer stresses they are the house bank and made different, not for starting.

BTW, there is a Lithium starter battery in my high compression 1300cc V twin motorcycle. On it's fifth or sixth year now, it spins the starter like it's a moped. (earthX)

Concern is with this unsophisticated charging system sending too much voltage to expensive lithium batteries. If it was an inboard with alternator then an adjustable regulator could solve the problem. Also too much voltage probably will shut down the solar side as it senses this voltage.

Maybe the 2 OB's and a start battery could be isolated ... never to see the house bank?

any thoughts?
good info out of you guys so far. Especially the informative links.

Your concerns about not being able to use an externally regulator alternator are correct. And also, the small alternator on the outboards would be destroyed by the large current demands of the LFP battery.

That is why I really *really* strongly suggest you use a lead-acid battery for starting. A small lead-acid battery will work fine, and won't damage your outboards alternator. Then, use a DCDC charger to charge your LFP. Very simple and inexpensive.

There is no advantage to using LFP for a start battery. It can work if certain requirements are met (externally regulated alternator, meets current requirements etc.) but it just doesn't offer any advantage over lead-acid for starting.

[sailingharry]

Originally Posted by wholybee

Your concerns about not being able to use an externally regulator alternator are correct. And also, the small alternator on the outboards would be destroyed by the large current demands of the LFP battery.



That is why I really *really* strongly suggest you use a lead-acid battery for starting. A small lead-acid battery will work fine, and won't damage your outboards alternator. Then, use a DCDC charger to charge your LFP. Very simple and inexpensive.



There is no advantage to using LFP for a start battery. It can work if certain requirements are met (externally regulated alternator, meets current requirements etc.) but it just doesn't offer any advantage over lead-acid for starting.

I think you're concerns and thoughts apply to more conventional boats. This boat is different.

First, using his house battery for a start Bank should be trivial. These are dinghy size outboard motors! If he sees 50A of starting current I would be truly surprised. In addition, adding a dedicated start system would be unnecessary added complexity. It doesn't really even add reliability and redundancy, as I am sure it is easily pull started. The outboard on my dinghy is the exact same size and doesn't even have the option of electric start.

I know that factory alternators are routinely burned up by large battery banks. But I don't know that I have heard any discussions about the charge system in small outboards. They certainly aren't alternators. I don't know how it would respond to a continuous 6A draw. That is not a lot of energy.

I'm not sure that the available charge current is worth any expense to make it usable. A DC to DC charger would be a challenge, the smallest one I've seen is 9a, more than his alternator is rated for (although if he had both engines running at full throttle, it would reduce total demand by 25%). To effectively accomplish this objective, he would need two 4A dc/dc chargers (maybe 3A would be better?)

To address OP's comment up thread about the voltage shutting off the solar. That doesn't actually happen in practice, and if it does it's not a problem. All that the entirety of charging systems does is seek to get a battery voltage. If one charger, for instance the alternator, gets the battery to 14.2 and the solar shuts off at 14.1, you have achieved the goal of 14.2. In reality, you'll be struggling to get to 13.8 and all systems will be producing maximum available power. In other words, If the alternator causes the solar to turn off, you don't need the solar at that moment.

[Nicholson58]

Post #10. Valid points.

A bit of research on small OB charging capability is in order. We are all assuming the worst in that the tiny alternators will charge a deeply depleted battery. The OP has significant solar so batteries may need only a top-up most times. I still believe it’s worthwhile to see if the alternators can be switched off if they are not capable of continuous full load output.

Our experience living off grid is that no amount of solar can account for a few poor consecutive days. We use our generator to top up. If plugging in is not an option then a very small gen-set might be in order. This would relieve the alternators from ever charging low batteries. We occasionally see small boats set up in the Caribbean with a tiny portable that is brought on deck for this purpose. PLEASE get an upgraded muffler

[JBP]

Most small outboards do not have an alternator for charging. They use a magneto coil aka "Lightning coil" and a rectifier. It will put out up to 80W depending upon RPM. You can safely leave this unconnected if you wish (check your engine manual). These can overcharge and put out a too high voltage. Your BMS should protect your battery, but I'm unsure if a disconnect would harm a magneto charger. What I do is leave the magneto output disconnected unless I really need the charge, in which case the voltage will never go too high until the battery is fully charged.
Alternatively, you could just use DC-DC charger from your house bank to keep the start battery topped up.

[team karst]

Most of my old school outboards regulate the charge winding by using a shunt regulator. Dissipating as heat enough current to keep the voltage from soaring. I believe omc had a scheme for water cooling the regulator which gives some idea of the waste heat.

[Nicholson58]

Adding a lead house battery and dc-dc adds cost and inefficiency but does not change the metrics. The lead battery will dump into the house until it’s full and the alternator will run constantly to recharge the lead. The dc-dc can slow the transfer but will impose inefficiency losses. For this system, the KISS method would be my choice. Better to figure out if the OB charging can take the load. I wonder if there is a YouTube video where a shade tree mechanic has repurposed a magneto system to make dc?

[wholybee]

Originally Posted by sailingharry

I think you're concerns and thoughts apply to more conventional boats. This boat is different.

First, using his house battery for a start Bank should be trivial. These are dinghy size outboard motors! If he sees 50A of starting current I would be truly surprised. In addition, adding a dedicated start system would be unnecessary added complexity. It doesn't really even add reliability and redundancy, as I am sure it is easily pull started. The outboard on my dinghy is the exact same size and doesn't even have the option of electric start.

I know that factory alternators are routinely burned up by large battery banks. But I don't know that I have heard any discussions about the charge system in small outboards. They certainly aren't alternators. I don't know how it would respond to a continuous 6A draw. That is not a lot of energy.

I'm not sure that the available charge current is worth any expense to make it usable. A DC to DC charger would be a challenge, the smallest one I've seen is 9a, more than his alternator is rated for (although if he had both engines running at full throttle, it would reduce total demand by 25%). To effectively accomplish this objective, he would need two 4A dc/dc chargers (maybe 3A would be better?)

To address OP's comment up thread about the voltage shutting off the solar. That doesn't actually happen in practice, and if it does it's not a problem. All that the entirety of charging systems does is seek to get a battery voltage. If one charger, for instance the alternator, gets the battery to 14.2 and the solar shuts off at 14.1, you have achieved the goal of 14.2. In reality, you'll be struggling to get to 13.8 and all systems will be producing maximum available power. In other words, If the alternator causes the solar to turn off, you don't need the solar at that moment.

It's valid that outboards are very different than an inboard. To that, the OP needs to contact Yamaha. I would expect that they would recommended against charging a Lithium. If they give charging a Lithium a blessing, that opens up other options. I would still opt for lead-acid, because a start battery is always at full charge, and the alternator will be charging or floating whenever the engine is running, and that will ruin an LFP. Plus, LFP is a lot more expensive, for no benefits in a start application.

A constant voltage source like a simple alternator is not appropriate for charging an LFP battery. It is valid that the smallest available still exceeds the rating of the alternator. But you still need one to charge the LFP without damaging the battery. It won't hurt the charger if only 4A are available. It will just charge at the lower current.

To be perfectly honest, anything less than about 10A isn't even worth it. I would use Lead acid for start, not connect the engines to the LFP at all, and invest the money saved in solar. A single 100A solar panel will do more charging than his engines will.