dc-dc CHARGING

[Mango boat]

According to what I've seen on the Renogy 20A DC-DC charger it has an input to turn it on and off via D+ (engine on) input. That is usually connected to the ACC circuit so when the alternator is on and charging, the Renogy DC-DC will be charging the LiFePo4 house bank. If you are running the engine then you should be monitoring all systems on your boat. Put an ON/OFF switch on the D+ line and you can manually shut your charger off when your house bank has reached full charge. Your alternator will continue to keep the FLA engine battery topped off and you won't overtax it.

This should protect your alternator and keep everything easy and clean.

I know but 20A is enough if I may believe Will Prowse
I have a 280Ah LifePo4 in my Ducato from 2011, no smart alternator.
LifePo can handle more amps but I don´t know if my alternator can handle that and to be save I am intent to buy the 20A version

 

[John Frum]

According to what I've seen on the Renogy 20A DC-DC charger it has an input to turn it on and off via D+ (engine on) input. That is usually connected to the ACC circuit so when the alternator is on and charging, the Renogy DC-DC will be charging the LiFePo4 house bank. If you are running the engine then you should be monitoring all systems on your boat. Put an ON/OFF switch on the D+ line and you can manually shut your charger off when your house bank has reached full charge. Your alternator will continue to keep the FLA engine battery topped off and you won't overtax it.

This should protect your alternator and keep everything easy and clean.

That is great and I would definitely put a switch in that circuit but...
I would not use it for charge termination on "battery full" because the charger already has logic for that.
It could not determine when to switch to float voltage otherwise.

 

[Mango boat]

But what if we drive and the alternator is 14,4V ?
What does the DC-DC charger do ?

Your DC-DC will be connected to your engine start FLA battery and regulate the voltage for your LiFePo4 battery.

Does your LiFePo4 battery have a BMS? That will protect against overcharge if you have one installed properly.

 

[Sabre36]

Thanks, I have not yet bought one but will buy a Renogy 20A because the Orion TR 12/30 is twice the price of a Renogy and I think it will do the same.

We have seen more Renogy components fail than just about any other brand, and they have only been around, as a "sticker applicator" company, for a few short years. Solar controller fires, solar panel hot spots that have started fires (after numerous fires they finally recalled/stopped selling these panels), solar panels that don't meet spec (lots of them), solar panel frames as flimsy as a beer can, and even B2B chargers DOA. You do tend to get what you pay for.

 

[grizzzman]

Why would it not terminate a charge in lifepo4 mode?
It can terminate the charge whether or not it goes to float.

Well, I have the 40 amp unit. To be fair I have sent a request for information to Renolagy. I will post the answer.

 

[Mango boat]

I would not use it for charge termination on "battery full" because the charger already has logic for that.

The Renogy 12-12 20A charger don't cut off at full charge. The charge profile just drops .2V when the batteries are at 90% and keeps charging (what you call "float"). As long as the D+ line is ON or HI the charger continuously does its job. It's not a super smart charger. I didn't read the specs on the Victron 12/12 30 but I suspect it doesn't shut down either unless it can sense a full charge through a smart BMS.

On the other hand, a BMS will shut down and protect against overcharge. But then you have a charger trying to push 14.4v @20A into a battery that won't accept a charge. What's the point?

There's no reason to keep the charger on all the time so the switch gives another control over how you charge. You don't need to keep the battery above resting voltage (13.6v) for extended periods. From what I've studied, they don't like to be at that level anyway. It could limit the life of the LiFePo4 battery taking it to 100% SOC and keeping it there for a long time.

What if you have a full charge from your solar panels and now you need to run the engine? Do you want your charger on? I'd like to have the option.

 

[John Frum]

The Renogy 12-12 20A charger don't cut off at full charge. The charge profile just drops .2V when the batteries are at 90% and keeps charging (what you call "float").

https://www.renogy.com/content/Manual/DCC1212-204060-Manual.pdf

On page 19 of the linked manual...
Charge voltages of 14.4, 14.1 and 14.7 are configurable.
I would choose 14.4 for charge voltage.
Float voltage of 13.5, 13.2 and 13.8 are configurable
13.2 is a safe choice and well exceeds than a 0.2 volt drop you mention.

 

[Mango boat]

We have seen more renogy components fail than just about any other brand... even B2B chargers DOA.

I agree that you get what you pay for. I'm probably going with a Victron of something a little more suitable for a marine environment. But, if you get a Renogy and it works as advertised then more power to ya (pun intended).

 

[Mango boat]

https://www.renogy.com/content/Manual/DCC1212-204060-Manual.pdf

On page 19 of the linked manual...
Charge voltages of 14.4, 14.1 and 14.7 are configurable.
I would choose 14.4 for charge voltage.
Float voltage of 13.5, 13.2 and 13.8 are configurable
13.2 is a safe choice and well exceeds than a 0.2 volt drop you mention.

Keep reading... page 21 is for LiFePo4 setup.

 

[John Frum]

Keep reading... page 21 is for LiFePo4 setup.

Personally I would use one of the profiles from page 19 that has float.
The lithium profiles on page 20 explicitly claim that they don't float so not sure where the .2 volt drop you mention is coming from.

 

[Mango boat]

I would not use it for charge termination on "battery full" because the charger already has logic for that.

Where does it say it cuts off the charge via "logic"?

BTW, on page 21 you can change the charge profile in .2V steps or increments. Why wouldn't you want to use a LiFePo4 charging profile?

 

[John Frum]

Where does it say it cuts off the charge via "logic"?

I'm glad you asked.
It doesn't say "logic" but if it can transition to float that is what it means.
And if it can transition to float then it has the logic capability to terminate at the end of absorb.

 

[Mango boat]

I'm glad you asked.
It doesn't say "logic" but if it can transition to float that is what it means.
And if it can transition to float then it has the logic capability to terminate at the end of absorb.

But it doesn't terminate at the end of charge (is that what you mean by "absorb"?). It continues charging doesn't it? You said earlier that you wouldn't use a switch to terminate charging "on battery full because the charger has the logic for that". I think if you go look at your post it implies the Renogy has the logic circuit for that and will sense the "battery full" and shut down. But it don't.

My contention is that if you are running engines and your battery becomes fully charged then you can turn off the charger.

Lots of chargers can transition to float. If doesn't mean they will automatically stop charging when the battery is at 100% SOC.

 

[John Frum]

But it doesn't terminate at the end of charge (is that what you mean by "absorb"?). It continues charging doesn't it? You said earlier that you wouldn't use a switch to terminate charging "on battery full because the charger has the logic for that". I think if you go look at your post it implies the Renogy has the logic circuit for that and will sense the "battery full" and shut down. But it don't.

If the Renogy can transition to float it uses charge termination logic in order to do that.
Seems you are not picking up what I'm laying down.
I'm going to stop now.

 

[Mango boat]

I would not use it [a switch] for charge termination on "battery full" because the charger already has logic for that.
It could not determine when to switch to float voltage otherwise.

I was just trying to get you to see the folly of your post. Not start a battle. Anyway, have fun.

I know what works for me on my sailboat with a hybrid FLA-LFP4/solar/dual engine charging system.

 

[John Frum]

I was just trying to get you to see the folly of your post.

You failed.
I don't think my post contained any folly.

 

[John Frum]

Well I guess I'm not done yet.
Page 22 describes the charge termination logic.
phase 2/absorption/constant voltage is limited to 3 hours.
Crude but effective charge termination logic.
Is there any folly in this post?

 

[Nol]

Oeps lot of answers today I try to read them all
I know that the Renogy need a D+ wire and I can make a switch in the line but I also have a BMV700 and maybe that one can switch the Renogy if the battery is 90% ful.
Otherwise the LifePo4 have a BMS which is between the battery and the BMV700 shunt. The otherside of the shunt is connected to the frame of the RV what mean that the BMS regulate the charging of the Renogy or am I wrong ?
Maybe my drawing clear what I mean.

I still have not bought a Renogy because they are not so common here in the Netherlands but the Victron Orion TR is very populair but much more expensive, twice the price of a Renogy.

 

[Mango boat]

Is there any folly in this post?

Yes, I don't think you understand what you are reading.

 

[John Frum]

Yes, I don't think you understand what you are reading.

Yeah, whatever.