LiFeP04 charge controller recommendations

[john61ct]

Battle Born gave me very specific instructions for how to correctly program a charger for their batteries. The batteries that they gave me a 10 year warranty on. Just stay away from cheap batteries from a faceless company....

10 years is nothing.

Obviously top notch cells are required and readily available, much better than what BB uses.

Which they don't even disclose, and can change anytime.

Remember they just assemble, not actually manufacture.

Drop-ins' interior BMS is opaque, no way to see per-cell voltages, no way to know if balancing is complete or not

setpoints can't be adjusted or disabled, no communications to the outside, and they can suddenly isolate the battery with no warning.

Special steps must be taken to ensure this can't damage charge sources or sensitive load devices.

Terminating charging when full, or when temps get too low or too high, should be able to signal other gear, or controlling generic relays.

As opposed to simply taking a batt offline without warning, which load dump can cause damaging spikes/surges.

The BMS can't be bypassed, even to check on the cells' voltages, and often drastically limits charge / discharge C-rates to a tiny fraction of LFP's capabilities.

LFP is capable of accepting very high charge rates, no problem. To the point that 2-3 day's worth of energy can be pumped back into the bank in an hour or two if you have a high-current charge source available. But the cheap included BMS in drop-ins prevents that, restricts you to a slow charge (and discharge) rate.

Check to see if they even allow serial or parallel connection into a bigger bank?

Allowing the "Full" or "Too Low" setpoints to be adjusted by the user to extend lifespan. The balancing function may require a charge voltage that is higher than what you want for longevity.

Allowing the user to even **see** the state of cell balance, verify that BMS function is working.

Allowing a cell to be swapped out if one proves faulty.

All impossible with drop-ins.

 

[john61ct]

Battle Born gave me very specific instructions for how to correctly program a charger for their batteries.

BTW I am not saying that BB is bad

nor that for some people drop-ins may suit their needs

Just that I personally have not found one yet that I would recommend as good value & max longevity.

You do you man.

 

[ducktapeguy]

So what kind of information can you get from the bluetooth system? I can get the basics from from my battery monitor, though some of it is from inference. For example, I might see 10A coming in (typical for my setup) but I know the fridge is running which typically draws about 8A, so the solar must be taking in 18A. But it's far from perfect, requires more thought, etc. Very often I would actually have to manually shut off all the loads so that I could understand what was actually coming in. The flipside though is that, as I get more comfortable with living with the system I built, I really don't want to concern myself too much with this anyway. I've already done 4 days in a row with cloudy weather, no driving, and no shore power, and we only went down to 30% battery without too much sacrifice.

The big thing for me is more control. For example, telling it to take 30A from the alternator, or not, instead of having to actually go and unplug my panels, etc.


Yeah, that's exactly the issue, and the system does not do what's expected. It's two 15A circuits, and if it's getting 0<x<15A from solar, it should take 15A from the alternator on the other circuit. But it does not. It won't even start to draw from the alternator until the solar is down really low, like 5A. So, I might be driving all day, and know the solar is not coming strong, and the batteries are low so I want to charge them as much as possible. I have to actually unplug the solar so that it pulls from the alternator.

This is what the app screen looks like. It just gives basic information like how much power (volts + amps) are coming from each source and how much is going to each battery. There are little arrow between each icon which show the direction of flow similar to the dash of an EV car. However, there's a bug in the app because the arrows don't always match the direction of power flow, specifically when the solar is charging the starting battery. It always shows power flowing FROM the starting battery to the controller, no matter which direction it's going. Also, I have to keep reconnecting it to bluetooth every time I want to check. The app was upgraded recently, the previous version seemed a lot better.


Do you have the IGN signal wire connected? I wonder if the panel is keeping the voltage high enough that the alternator input is switching over. That's kind of what it sounds like is happening. Does putting a load on the house battery cause the alternator charging to kick in? If you want it to prioritize the alternator charging when the engine is on you may have to rewire to automatically disconnect the panels when the engine starts.

From the manual. I haven't really studied it enough to figure out the charging logic of this charger.




One thing I noticed is the my power draws act differently when I switched to LiFeP04 batteries and a DC/DC charger. Before, when my fridge kicked it, it was easy to see the added power draw on my charging circuit, because the battery voltage would dip, so the charging amperage would go up correspondingly. So if I was charging at 5A, and the fridge starts up drawing 5A, my total charging current would increase to 10A. However, with the Li batteries, there is very little voltage drop under load, so the input charging current doesn't really change much when my fridge or other accessories are on. Seems that the charging is somewhat independent of the loads at least temporarily

It's working well enough for now that I haven't really messed with it anymore and don't really check it that often. So I guess that can be considered a success, when I don't have to put any more thought into it.

I'm sorry I missed where you said you tried it and it didn't work. I saw where you said you read about it. Did you set up your system exactly like the diagram I posted? It seems to work well for the user that posted it on the other forum, and after reading numerous posts from him, he seems to know a little bit about electrical and solar.

What problem did you run into?

I set it up to mimic a DC/DC charger. It was only for testing, so no LVD or relay or solar panel input, just step up converter and MPPT controller. But same converter and controller as in your picture. The problem I had was the Victron controller was showing it was sucking max power (20A@24V) out of the converter but not delivering that power to the house battery, so most of that power I *think* was getting dissipated in the controller. The reason mentioned earlier in this thread make sense, the output of the converter does not simulate a solar panel output curve very accurately, so the MPPT controller might be getting tricked. Maybe there is an easy fix for this problem, but like I said it wasn't worth the trouble for me to investigate. There were a couple of reasons, the main one being I didn't want to trust a $20 converter to not burn my truck down, a couple of hundred watts is a lot of power if something happened to go wrong. Also, I would have had to add in some extra relays and wiring to switch the converter off when the engine was shut off because I didn't trust it. For me it wasn't worth the trouble to save $100 and deal with those headaches. I would think if it were as easy as adding in a cheap boost convter to an MPPT controller, Victron/Redarc/Renogy wouldn't be making these huge DC/DC chargers that cost a couple hundred bucks.

 

[Rando]

I saw this in another forum: Using an MPPT as DC to DC

Any reason why this wouldn't work or would be dangerous (I think this is along the same lines of what is being discussed in this thread)?


View attachment 681132

Pretty sure that is my diagram, and this has worked well for me for several years. However I enjoy tinkering, if you just want the most straightforward solution, just buy the Victron DC-DC charger.

 

[Rando]

I set it up to mimic a DC/DC charger. It was only for testing, so no LVD or relay or solar panel input, just step up converter and MPPT controller. But same converter and controller as in your picture. The problem I had was the Victron controller was showing it was sucking max power (20A@24V) out of the converter but not delivering that power to the house battery, so most of that power I *think* was getting dissipated in the controller. The reason mentioned earlier in this thread make sense, the output of the converter does not simulate a solar panel output curve very accurately, so the MPPT controller might be getting tricked. Maybe there is an easy fix for this problem, but like I said it wasn't worth the trouble for me to investigate. There were a couple of reasons, the main one being I didn't want to trust a $20 converter to not burn my truck down, a couple of hundred watts is a lot of power if something happened to go wrong. Also, I would have had to add in some extra relays and wiring to switch the converter off when the engine was shut off because I didn't trust it. For me it wasn't worth the trouble to save $100 and deal with those headaches. I would think if it were as easy as adding in a cheap boost convter to an MPPT controller, Victron/Redarc/Renogy wouldn't be making these huge DC/DC chargers that cost a couple hundred bucks.

I am sure it was not dissipating the power in the controller, it would have gone up in smoke immediately if it was. If you are using the load terminals on the controller, the controller subtracts the power passing through those from the input power to give you the net power to the battery. If you had a decent sized load running, that would explain the apparent difference. I know in my implementation of this power in = power out.

 

[R_Lefebvre]

This is what the app screen looks like. It just gives basic information like how much power (volts + amps) are coming from each source and how much is going to each battery. There are little arrow between each icon which show the direction of flow similar to the dash of an EV car. However, there's a bug in the app because the arrows don't always match the direction of power flow, specifically when the solar is charging the starting battery. It always shows power flowing FROM the starting battery to the controller, no matter which direction it's going. Also, I have to keep reconnecting it to bluetooth every time I want to check. The app was upgraded recently, the previous version seemed a lot better.

Wow, that sounds crappy and not super useful. Thinks like mess bluetooth connectivity really drive me nuts so I'd rather avoid the hassle.

Does it allow you to change the settings on the DCDC? ie: I would like to drop the max charge voltage from 14.4V to maybe 13.6V or something.