LifePo4 charging via dc to dc

[ben373]

I thought I had a good plan but have come a little undone.

Looking for ideas and info for others.

I have a d1-20f Volvo with the Mitsubishi 115amp alternator.

I have 300amp of 4 x Calb cells with a Daly BMS

The alternator goes to a combiner schottchy type start and house batteries.

House side onto the DC to DC and then the BMS

Dc to Dc charger is a new Renology 40amp set for LifePo4

I have 2 issues;

1 the alternator can charge the batteries at 100amp if the dc to dc is not in circuit but of course gets hot at 100c when running for 20 mins. does not seem to De rate. It's stops charging suddenly when the BMS disconnects. As the start battery is in the circuit it seems okay with the surge.

Also when fully charged it cuts out and a min or so later cuts back in. You can feel the load go on and off the motor.

2. My solution was the DC to DC. It works fine limited to 40 amp. The unknown was that when the alternator is producing less than 40 amps the input side gets pulled down to 9v. After a min or so the engine throws an alarm for low voltage or alternator not charging which it is. Annoying.

Apparently, this 9v on the input side is by design so as to make the alternator work hard. I imagine they are designed to be put in a trailer where there is a large voltage drop from the alternator in the tow vehicle.

I was thinking maybe a temp operated solenoid to just kick in the dc to dc when the alternator gets to say 90c maybe a solution.

This post is to supply info for others and to look for ideas.

I am an Electrician by trade but 1st time with lithium.

I am handy with an Andrino and sensors.

I would like to solve this with what I have rather than go to external regulation of the alternator. My alternator is almost impossible to remove without moving the engine forward.

3. I am also looking for info the Mitsubishi 115 amp with regard to temperature.

4. I am looking for info on the Daly BMS in terms of what the settings should be. I have Bluetooth to it which works very well.

My boat is day racing and weekend cruising. Really nice to have all this power that's for sure.

Sorry for the long post..

[smac999]

Why are you running the dc to dc inline with the battery isolator?

Connect the alt direct to engine battery. Dc to dc goes from engine battery to hiuse battery. Make it engine or voltage triggered. Get rid of battery isolator.

The bms should never be shutting off a battery while charging. The bms shuts down for emergency only. Ie high voltage.

[ben373]

Originally Posted by smac999

Why are you running the dc to dc inline with the battery isolator?

Connect the alt direct to engine battery. Dc to dc goes from engine battery to hiuse battery. Make it engine or voltage triggered. Get rid of battery isolator.

The bms should never be shutting off a battery while charging. The bms shuts down for emergency only. Ie high voltage.

Thanks for the info. Yes I can now get rid of the combiner although it is a modern type and seems to be no problem.

Unfortunately, I don't think it will make a difference to the low volts on the input side.

The is for the info re the BMS it is basically a safety?

[Corvidae]

Yeah, the BMS is a safety cut off in case of High/Low volts or temps. Lithium is great stuff, but gets really angry if you push it out of operating range.

The biggest problem I've been running into are battery chargers running in AGM or Flooded mode. Part of their cycle is to desulphate the batteries by throwing over voltage at them when fully charged. Keeps lead batteries in good shape, and shuts down the BMS on lithium batteries real quick. Lithium doesn't need a battery charger, it needs a power supply set to the charging voltage.

[AllenRbrts]

Based on the info provided seems like you have two major issues.

1 dc to dc charger is most likely programmed to lead acid. Which is why the bms shuts down. Your charger can programmed to lithium.

2. Your dc to dc charger is either on or it is off, it isn’t adjusting its output when your alternator output is low (idle). You might need to upgrade to a smarter charger which detects the input voltage to decide when to charge. You might smoke your alternator with current setup.

[ben373]

Originally Posted by AllenRbrts

Based on the info provided seems like you have two major issues.

1 dc to dc charger is most likely programmed to lead acid. Which is why the bms shuts down. Your charger can programmed to lithium.

2. Your dc to dc charger is either on or it is off, it isn’t adjusting its output when your alternator output is low (idle). You might need to upgrade to a smarter charger which detects the input voltage to decide when to charge. You might smoke your alternator with current setup.

Thanks the Dc to dc charger is on for the Lithium system. The system can be set from 13.0 to 14.6 volts with several settings in between. I have selected 14.4v it seems to be on or off, no float.

[AllenRbrts]

Originally Posted by ben373

Thanks the Dc to dc charger is on for the Lithium system. The system can be set from 13.0 to 14.6 volts with several settings in between. I have selected 14.4v it seems to be on or off, no float.

Perhaps a more general statement is the charger is doing something the bms is unhappy with. Perhaps measure some voltages near the point of disconnect. Are all the cells the same voltage? At what voltage does it disconnect?

[rphdiego]

Install a Victron Li-ct 120a battery combiner between your start and lithium house bank.

[Cpt Mark]

following

[Nico Domino]

LifePo4 have their own built in bms. The simple thought is to put a lead acid battery In parallel with the lithium. If you look at charge/ discharge graphs of both types, they compliment each other and further more they self regulate. We r constantly told not to mix them, however, it appears that it may be a happy marriage at least on paper.

[Hzale]

Typically the energy DC to DC charger goes on when you turn the key on and it gets 12 volts from the starter battery, I put a switch in line in my system from the starter key to the start input of the charger. That way while the engine is idling or warming up I don't have to worry about over stressing the alternator, then when I'm at cruising RPM I flick the switch and let the battery charge. I try to shut it down before it gets to 100%, but it doesn't really matter because the BMS will shut it down if I forget. The worst is if you slow down to idle to dock or anchor and the battery is not fully charged then the alternator can't put out enough and the starter battery gets depleted.

[Capt MikeC]

You didn't mention if you top balanced your cells or not, if not then the most likely cause of your BMS cutting off the charge is due to one cell exceeding the cut off voltage (the BMS cut off voltage is for the cells not the whole battery). I have a Daly Smart BMS (it has blue tooth) so I am able to watch the cell voltages (as read by the BMS) as the cells charge. As the state of charge reaches 90% or more the voltage differences really show up, so as someone else mentioned track the cell voltages as your battery nears the end of its charging. If you haven't top balance your cells do so, it will allow you to get more capacity out of your battery and helps avoid abusing cells whose State of Charge (SOC) is higher than the rest.

I have a Victron DC to DC 30 Amp charger and it allows me to set the minimum input voltage, hopefully your DC to DC charger allows you to do the same. I set the minimum to the 50% SOC voltage of my AGM starter battery, to protect the starter battery (12V). The Victron also has two pins that you short together or set one pin high or the other pin low to enable charging, I put a switch on it so I can manually decide when I want the LiFePO4 batteries to charge.

[Simi 60]

Originally Posted by rphdiego

Install a Victron Li-ct 120a battery combiner between your start and lithium house bank.

Probably not
I have that exact model on ours with a large AGM bank and pretty sure its killed off the new alt.

[wholybee]

Having the isolator and the DCDC charger both probably is causing your issues. So start with getting rid of it and connect it as the manual describes. The DCDC charger is not designed to be connected to the alternator, but to another battery.

The Renogy should have a D+ terminal. What do you have that connected to?

The problem with the isolator is that the input of the Renogy can drop too low if the alternator isn't putting out enough current. But, if the D+ is connected to the IGN from the Start battery, then that will still be 12V, and the Renogy will not know to shut down or reduce output.

Do you have the model that can reduce output by half? It would be worth while to connect that to a switch.

[Dsanduril]

If you are willing to part with the $, Nordkyn Design has the VRC-200, an external "regulator" of sorts built specifically for the D1/D2/D3 alternators. Rather than being a traditional regulator it allows you to use the voltage sensing input on the alternator to control the internal regulator.

Specifically built for LiFePO4 systems and the 115A Mitsubishi alternator found on Volvo engines. Even if you don't want to buy his product, Eric has some excellent articles about wiring up/charging lithium banks with LA starter batteries.