32 volt Battery to Battery Charger?

[Trying Not To Sink]

Is anyone aware of a way for me to charge my house bank (24volt Lifepo4) using my alternators (32 volt alternator and 32 volt starting bank) while underway? I have seen B to B chargers that do this, such as the Renogy and Sterling, but I have not found one that handles 32 volt input.

My backup plan is install an additional direct drive 24 volt alternator on my Detroit Diesels (8v92) but those things cost over $1500 and I would still need the B to B charger. Victron makes a Dc-Dc Converter with the right voltages but it is only 12 amps and, I assume, doesn't have the ability for multi stage charging.

Any ideas would be appreciated.

 

[DThames]

CC, CV buck charger. Smaller and cheaper option.

 

[Trying Not To Sink]

Thank you for the response. If I used converters like those would I need to monitor the batteries state of charge, and manually disconnect the converter or do you just set them to the float voltage and let them run?

There seems to be such a big price range in Dc-Dc converters, ranging from inexpensive, like those listed above, to costing several hundred dollars, like the Newmars that I use on my boat to step down from 32v to 12v to run navigation equipment. What's the difference?

 

[DThames]

Thank you for the response. If I used converters like those would I need to monitor the batteries state of charge, and manually disconnect the converter or do you just set them to the float voltage and let them run?

There seems to be such a big price range in Dc-Dc converters, ranging from inexpensive, like those listed above, to costing several hundred dollars, like the Newmars that I use on my boat to step down from 32v to 12v to run navigation equipment. What's the difference?

There are two adjustments, one for max current, one for max voltage. CC-CV means it does a Constant Current until the set voltage is reached. Then that voltage is held (Constant Voltage) and the current is reduced until the battery is fully charged at that voltage. It basically stays "on" but doesn't charge until there is need to. If you load the battery at all, it will start trying to make up for the power going out of the battery.

I am sure there are many differences but a board without a box (cheaper) is the first thing that comes to mind. You normally have to provide extra cooling if you want the full rating. I would guess that more expensive units have more parameters that you can set, like the voltage that they will kick back on at. For Lithium, CC-CV works well. You can set it to charged to any voltage, so you can do 3.5v, 3.55v, 3.6v per cell or whatever makes you happy.

Those cheap boards should work fine parallel, but I have not tested that. I have a couple of 300w units that are step up (boost) type, but have not got around to parallel testing.

 

[DJSmiley]

However, if you do use these, they will keep the batteries at a very high SOC. If you set them to 3.5 or 3.6, it will always provide that to the cells, eventually overcharging them.

A good charger does goes to float once the batteries are full, a buck-boost converter doesn't.

Cheap way to use 32V to charge a 12 or 24V power bank, fully maintaining proper charge profiles, is using a MPPT solar charger. Instead of a PV panel, just hookup the 32V. That will work perfectly.

Don't know about the amps you want to provide to your bank, but eg a Epever Tracer 4210AN would make a great 40A charger.
The Evpevers require at least +2V input on the PV side, so for a 26V for a 24V bank, and with 32V you're fine)

Adjust the settings as mentioned eg by Will

(Disable temp coefficient, set boost to 14.4V, float to 13.6V ( https://www.mobile-solarpower.com/design-your-own-12v-lifepo4-system.html )

The Victrons are $$$ and the DC-DC doesn't have charging profiles, in that case you need the Orion SMART (the smart does feature charging profiles)

A MPPT charger like the Epever will just work perfectly as a B2B charger, PV input is up to 100V so basicly anywhere between 26 and 100V on its PV input will work fine. And its much more affordable. PV input doesn't mean its PV-only.

You can go even higher, but as with a DC-DC like the renogy, make sure your alternator is able to handle these loads continously for longer periods!

 

[DThames]

As previously stated, "You can set it to charged to any voltage, so you can do 3.5v, 3.55v, 3.6v per cell or whatever makes you happy." Or lower.

 

[DThames]

However, if you do use these, they will keep the batteries at a very high SOC. If you set them to 3.5 or 3.6, it will always provide that to the cells, eventually overcharging them.

A good charger does goes to float once the batteries are full, a buck-boost converter doesn't.

Cheap way to use 32V to charge a 12 or 24V power bank, fully maintaining proper charge profiles, is using a MPPT solar charger. Instead of a PV panel, just hookup the 32V. That will work perfectly.

Don't know about the amps you want to provide to your bank, but eg a Epever Tracer 4210AN would make a great 40A charger.
The Evpevers require at least +2V input on the PV side, so for a 26V for a 24V bank, and with 32V you're fine)

Adjust the settings as mentioned eg by Will

(Disable temp coefficient, set boost to 14.4V, float to 13.6V ( https://www.mobile-solarpower.com/design-your-own-12v-lifepo4-system.html )

The Victrons are $$$ and the DC-DC doesn't have charging profiles, in that case you need the Orion SMART (the smart does feature charging profiles)

A MPPT charger like the Epever will just work perfectly as a B2B charger, PV input is up to 100V so basicly anywhere between 26 and 100V on its PV input will work fine. And its much more affordable. PV input doesn't mean its PV-only.

An MPPT charger will try to pull its rated amps, which might be more load than you want on your alternator. Size according to load you want to see on your alternator.

 

[Trying Not To Sink]

Thank you both for all the information. It is very helpful.

My alternator puts out a maximum of 60amps. I was thinking that a charger capable of, or set at, 30 amps or less to protect the alternator.

If I use an MPPT, like the one mentioned above, would my 60 amp alternator damage the MPPT since it is a 40 amp charger, or does the MPPT just limit the throughput to 40 amps or less?

 

[DJSmiley]

the MPPT just limits it, the alternator is not pushing 60A, it can deliver 60A when requested.

Also, the 40A is on the battery side, the 24V side. At the PV side, it will be lower.

40A * 24V = 960 W. At a 32V input, that equals to about 960/32V = 30A. So it will draw approx 30A from the alternator. This is excluding losses in the MPPT, so in reality it would be approx 32A I think.

However, its unlikely the alternator is sitting idle. So from the 60A you have to substract the current from other equipment powered by the alternator. If using 40A for charging, lights, and other stuff, you can't pull another 30A for the house bank without overloading!

Also, make sure you check for the worst-case situation, so without any lights, and a fully topped battery doesn't give a realistic result about the 'basic' draw from the alternator.

to be on the safe side, you might also go for a 30 or 20A charger. Cheaper, and less stressfull on the alternator. Disadvantage is it's slower to fully charge the house bank.

 

[Trying Not To Sink]

Thanks. I understand now. You guys have been very helpful. Great forum!

 

[Trying Not To Sink]

The Evpevers require at least +2V input on the PV side, so for a 26V for a 24V bank, and with 32V you're fine)

Does this mean I will need to install some method of turning the MPPT off when the engines are not running, otherwise it could draw my 32 volt bank down to the 26 volts?

 

[DJSmiley]

If the engine isn't running, yes. It won't draw your bank to 26V, but it will continue to charge the housebank till it's full, so might drain the batteries.

If the housebank is already full, it won't be a major issue, but the mppt will still draw (although a little) power.

Easiest is to wire a relay in series between the 32V bank and the MPPT, and connect the relay to the D+ of the alternator if available. In that case, the relay will be only active when the alternator is running (thus the engine is actually running), so it will only charge the HH bank when the engine is really running.

 

[Trying Not To Sink]

If the engine isn't running, yes. It won't draw your bank to 26V, but it will continue to charge the housebank till it's full, so might drain the batteries.

If the housebank is already full, it won't be a major issue, but the mppt will still draw (although a little) power.

Easiest is to wire a relay in series between the 32V bank and the MPPT, and connect the relay to the D+ of the alternator if available. In that case, the relay will be only active when the alternator is running (thus the engine is actually running), so it will only charge the HH bank when the engine is really running.

Thanks. That is what I thought. I will check to see if I have a D+ available when I get back to the boat. If not, perhaps I'll use the ignition key to trigger the relay.

 

[32 volt boater]

Hi,

I am messing with 32 volts as well.

Solar charge 32 volt battery system on 1970s cabin cruiser - No one makes 32V stuff

Hi everyone, got a fun one here, 32 volts. So I already bought 18 100 watt panels and an outback Flexmax 80 charge controller. Interestingly making a solar top as it was the around same price as replacing the torn up canvas top. 2 or 4 panels to be dedicated to 12v. Haven't decided yet...

diysolarforum.com

 

[32 volt boater]

Oh cool, I did not know there was a marine section. I would have put my original post here.

 

[32 volt boater]

Anyway here https://diysolarforum.com/threads/s...bin-cruiser-how-to-do-32v-marine-stuff.44824/

I got 32 volt solar to work great.