Just double checking my planned LifePo4 set up

[Snowgoose35]

My plan is to change ti LifePO4 with around 400 ah to replace my current 600 AH lead acid

My solar set up is 1500w at 38v with two 60A Morningstar MPPT which I can program to give happy Lithium charging so this seems not a problem.

The other charge source however is my slight concern - I have two 125A alternators which are currently connected to the Lead Acids and then go back to charge the starters via a VSR. The worry is two fold - 1) that the draw if the LifePo are ever low could pull down the full 250A from the alternators for an extended time and over heat them 2) that the BMS on the batteries will cut the charge when full which could burn out the diodes on the alternators. The solutions to the second seems to be to parallel in a lead acid battery to take the dump load from the alternators if the BMS cuts off charge to the LifePO instantly

The solution to the first varies between using things like a BMS12/200 with a fuse sized to limit the charge (100amp being the greatest possible) or putting a lead acid in the system with a DC-DC charger from that to the LifePO which would obviously solve the dump load issue too but that seems to mean much lower charging rates of the LifePO when part of the advantage is fast charge acceptance.

So has anyone real world experience of one or other of these options or another way to set up to protect the alternators ?

[john61ct]

The two mainstream solutions to limit current are

A. put an adjustable VR on each alt, like Balmar MC-614

B. use DC-DC chargers, like Sterling's battery-to-battery line

If going to the latter, may need to stack more than one to get the amps desired, but can start with one and see how you go.

A BMS does **not** limit current, just like a fuse, either allows pass-through or shuts down, may need replacing.

There are other CL solutions, but required skillz and are controversial here.

Most will advise the A route.

[john61ct]

And there are high-tech solutions to prevent / absorb a load dump scenario from the BMS isolating the bank.

But I agree, if you go with A, then a small cheap lead batt in parallel will do.

If you go with B, just tap the DCDC input into the starter / alt circuit, often right at the Starter posts.

[john61ct]

Also note, the "putting a lead acid in the system" **only** helps with load dumps.

It does nothing wrt the required limiting of current demanded by the LFP.

What alternators do you have?

Have you determined what their real-life maximum continuous amps output limit is in hot ambient conditions?

[Snowgoose35]

No I appreciate that - what I said was a lead acid with a DC to Dc charger - its the DC to DC that will limit the current the LifePo can draw and the lead acid that is there for a dump load.
As I understand it the Victron BMS 12/200 can limit the draw but having a maxi fuse of the right value (max 100amp) in there - Victron say this will start to get hot when at about 80% of max load and the BMS senses this and reduces the current flowing to the LifePo thus saving the alternator.
I'm not sure yet exactly what the maximum continuous amps are from the alternators - they are the standard Hitachi 125 amp that come from Yanmar with new engines I am having installed - two engines on a cat so 250 amp total but unless I buy a lot of DC-DC chargers to stack up I won't get anywhere near that - the biggest I've found is 60a and at £300 each I doubt I would run to more than two in parallel to give 120a maximum - so about 50% max load from the two alternators . Does that seem sensible ?

[CatNewBee]

If you want real world experiance, here it goes.

On our cat with 2 yanmar 3jh5e 40hp engines, 2x 80A Hitachi alternators, separation diodes to charge house and start battery independently and upgrade to 1000Ah Winston LiFeYPO4, it works without fancy gimmicks.

The alternators internal regulators are factory preset to 14.2V (3.55V), well below 14.6V or cell voltage 3.65V what represents a full LFP cell. So in theory you will stay at bulk in regard to the BMS and never reach a BMS cut off.

But the problem is, your start battery may die over time when never going to absorption.

Real world experience: A 80A alternator provides about 40A to the LFP bank, most of the time sitting at 13.4V. Chances are, it never charges full.

I have however set up a disconnect relay (BlueSea ML-RBS 500A solenoid, bi-stable) controlled by the Victron BMV based on SOC, id connects the alternators if SOC drops below 85% and disconnects at 95%, so the start battery has a chance to go to absorption voltages above 14V. The start batteries remain always connected, so no problem dropping the house battery. No Balmar, no B2B, simply working now for 2 sailing season.

A big issue could be, if your house battery is small and you run a big inverter while charging by the alternators. Then the voltage may drop way below 12V, and the alternator delivers full power, gets hot and burns, as often happens in RV with small FLA house batteries and installed big after market inverters, then people try to back the battery by the engine and alternator as replacement for a generator, and fry the system, best case they burn a fuse, worst case, the regulator or alternator coil.

[john61ct]

Originally Posted by Snowgoose35

As I understand it the Victron BMS 12/200 can limit the draw but having a maxi fuse of the right value (max 100amp) in there - Victron say this will start to get hot when at about 80% of max load and the BMS senses this and reduces the current flowing to the LifePo thus saving the alternator.

If that does reliably work well, not just as a backup / failsafe occasional overcurrent protection, but specifically for regular charge current control in regular cycling, that would be rare, and to me very interesting.

By default in the meantime I'll be skeptical, I'd use it for the former usage only.

> standard Hitachi 125 amp that come from Yanmar

Someone will come along with hard data. By default in hot ambient I'd limit to 70-80A and monitor temps (both locations) while recharging the LFP for more than 30-min to an hour.

The Sterling BBWs go up to rated 120A, and I believe derate to half output. Compared to the BBs they are designed for outside use so the fan is noisier. Also the BBW require the optional remote for custom-user profile tweaking, while BB it's built in.

> about 50% max load from the two alternators . Does that seem sensible ?

Yes, starting conservative is wise, especially in hot temps.

Note that converting the alts to external VR, like Balmar MC-614, is a more mainstream solution, and has a great benefit of letting you set your desired max amps production in finer increments, as well as de-rating current automatically based on overtemp conditions.

Make sure not to charge the LFP bank too fast, especially in colder ambients. 0.4C rate is a good upper guideline for longevity, but when things get hot you could go faster if you have a strong reason to.

[Rorzech]

ElectroDacus has a great 120 Amp MPPT charge controller for $250 CDN , it also has a screen with a ton of info (SOG Temp voltage) from all 8 cells that are monitored and has 8 channel BMS. I just got one and my mind is blown with this small machine.They never gave me a deal. So I don't owe them anything.But it doesn't mean it isn't a great product !

[mitiempo]

You should look at the Wakespeed WS500 regulator for the alternators. Nothing I have seen - including Balmar - comes close for LiFePo4 charging.

Welcome to Wakespeed

[Q Xopa]

Originally Posted by john61ct

The two mainstream solutions to limit current are

A. put an adjustable VR on each alt, like Balmar MC-614

B. use DC-DC chargers, like Sterling's battery-to-battery line

If going to the latter, may need to stack more than one to get the amps desired, but can start with one and see how you go.

A BMS does **not** limit current, just like a fuse, either allows pass-through or shuts down, may need replacing.

There are other CL solutions, but required skillz and are controversial here.

Most will advise the A route.

Hmmm, Option A? I'm not actually sure if 614 actually 'limits current'. Current is controlled as a result of limiting voltage, as most VRs do. In fact my understanding is a 614 doesnt even actually even know what current the alternator is outputting. There is no shunt connected to the 614.

Also not sure what your logic with your suggestion B, a DC DC charger is?

Perhaps if you can explain to me what the sense of operating one not inexpensive device at max capacity to save running another not inexpensive device at max capacity and kill it from overheating it. You dont consider if you are running a DC DC charger at max capacity it will get hot and die prematurely?

Are you you actually doing, or seen this you are suggesting?

[ABJ87]

Originally Posted by Rorzech

ElectroDacus has a great 120 Amp MPPT charge controller for $250 CDN , it also has a screen with a ton of info (SOG Temp voltage) from all 8 cells that are monitored and has 8 channel BMS. I just got one and my mind is blown with this small machine.They never gave me a deal. So I don't owe them anything.But it doesn't mean it isn't a great product !

I believe it is only PWM. They have a version that also lets you control an external MPPT like the victron

[CatNewBee]

So what you are up to now, you've got 10 different opinions, some unrelated recommendations for MPPT and PWM controllers, b2b chargers, alternators, some real experience and observations with facts and some fiction.

I would be curious what paths you are going after all.

Btw. A b2b charger was originally developed for RV's to discriminate charge current to the start battery in favor of the house battery by putting maximum load on the alternator with resulting voltage sag and increasing the voltage on the output to the house battery by step up conversion to push more current into the house battery, also as side effect allowing multi stage charging from W charging to IUoU characteristics (bulk with constant current, absorption with constant voltage, float with constant voltage) to meet the requirements of SMF, GEL and AGM batteries. As a side effect because of the dessign limitations such devices act too as power limiter in larger installations, when the alternator power exceeds the capabilities of the b2b charger.

[Q Xopa]

Originally Posted by CatNewBee

So what you are up to now, you've got 10 different opinions, some unrelated recommendations for MPPT and PWM controllers, b2b chargers, alternators, some real experience and observations with facts and some fiction.

I would be curious what paths you are going after all.

Btw. A b2b charger was originally developed for RV's to discriminate charge current to the start battery in favor of the house battery by putting maximum load on the alternator with resulting voltage sag and increasing the voltage on the output to the house battery by step up conversion to push more current into the house battery, also as side effect allowing multi stage charging from W charging to IUoU characteristics (bulk with constant current, absorption with constant voltage, float with constant voltage) to meet the requirements of SMF, GEL and AGM batteries. As a side effect because of the dessign limitations such devices act too as power limiter in larger installations, when the alternator power exceeds the capabilities of the b2b charger.

Sure, no argument that B2Bs can work like this. I understand you can do this to reduce the load on your Alternator and increase its life.

My question is why you want to save your Alternator by running your B2B at its design limit which can shorten its life?

To me its like putting a big turbo engine in your car, drive it hard, but put your brakes on to not crash. Obviously your brakes wont last long.

My suggestion is to just dont drive so fast/ regulate your speed
by pressing your right foot less.

So to me using a Voltage Reg to throttle the Alternator output makes more sense.

Just my crazy thought, what do I know.

[smac999]

Originally Posted by Q Xopa

Hmmm, Option A? I'm not actually sure if 614 actually 'limits current'.

it does. via the belt manager setting. it will limit the max amps the alt can put out.



I just came across the victron oroin TR smart dc-dc. must be new, as they are now with 3 stage charging and blue tooth programming. and voltage sense turn on voltages. going to try some from a lead engine battery to lithium battery soon. just stack them for more amps. and keep total amps less then your alt to limit the max alt current. they make a 12-12 30a. looks cool. an echo charger on steroids.

[Q Xopa]

Originally Posted by smac999

it does. via the belt manager setting. it will limit the max amps the alt can put out.



I just came across the victron oroin TR smart dc-dc. must be new, as they are now with 3 stage charging and blue tooth programming. and voltage sense turn on voltages. going to try some from a lead engine battery to lithium battery soon. just stack them for more amps. and keep total amps less then your alt to limit the max alt current. they make a 12-12 30a. looks cool. an echo charger on steroids.

Yes true, indirectly.

Belt manager is usually for a set initial start up period. You could also use Small engine mode, if it is connected with a switch and programed. It reduces output, when selected, to approx 50%.

But this is not the intended use and has limited adjustable parameters so is not ideal to use for this.

But if it works for your application great.