diy solar

diy solar

DC-DC charger (B2B) options and general discussion

Just taking a step back here, am I correct in assuming that all of these smart chargers (other than Kisae, with limitations and the Nordkyn controller) rely on the BMS to terminate charging? That can't be right can it?
 
When it comes to charging an expensive battery bank, don't go cheap. Buy something that doesn't come directly from China. Go back to the beginning of this thread and look at the DC-DC chargers that forum members are using.
I agree with such approach especially when it refers to automotive parts.
But if I take my system- everything goes directly from China- cells, solar pannels, wires, terminals, epsolar mppt, bms, ballancer, dc compressor freezer.
I reviewed the dc chargers from the first page. They actually have a lot of additional functionality that I dont need. For me it is essential to limit alternator current, and limit ouput voltage. Also I dont need to use this charger 24/7 - just temporary backup power when the battery is low to avoid direct wireing. Besides current exchange rate at my country makes those above metioned chargers too expensive ((
 
I thought I was going to have to buy a lot of things on the Internet and have them shipped. Through a fair amount of digging, I found a couple of local sources. It wasn't easy to find them, but it saved me a lot of money, time and hassle.
 
The isolated DC-DC chargers will keep the two sides of your system separate even when connected. I'm probably explaining that horribly in technical terms, but that is the gist of it..... The main difference (maybe only difference is with the isolated the input and output circuits have their own dedicated negative, and the non-isolated have a common negative. In many cases this doesn't matter, in some cases it does.

Thank you for spelling this out. I knew they were different concepts but didn't understand what isolated meant in this context.
 
I read in another place that those renogy are factory programed to limit alternator charge to 50% of their amp rating as sooon as they detect any solar charging. The person who found the issue added as switch to disconect his solar while driving and emailed Renogy who confirmed his finding was programed like that and not a defect; although not advertise. Im glad I found it before I bought it.
To be fair, the device's behavior is described in the manual.
 
I do not know if what you ask is feasible, but 13.8v isn’t enough to charge a 12v lifepo4 battery full.

My understanding is that 4S LFP is* full (100% SoC) at 13.8v / 3.45v/cell. MarineHowTo says, "The reason drop-in makers suggest such high voltages is because balancing is typically done at the top-of charge with a FET based BMS".

So maybe we could say 13.8v is enough to get a 12v LFP full but not necessarily balanced. I mention the distinction because if the proposed CV charging solution were running in parallel with solar that charged to 14.x for balancing regularly perhaps it would work ok.** Dunno. I might want <= 13.6v output to avoid holding the cells at 100% for long driving periods, still relying on solar for 14.x voltage.

-----
* or can be
** not necessarily recommending using that device, just working through the concepts for my own curiosity
 
The issue there is that I'm trying to follow the charging recommendations of Nordkyndesigns and none of these chargers appear to shut down properly (when current gets down to .033C) and would seem to overcharge the pack (were it not for the BMS). Well, the Kisae DMT series actually does but they max out a 10A for the low current shutoff but that would work for a battery of up to 300Ah and I plan to install 560Ah. As best I can tell, all these 'smart' chargers aren't that smart and the 100% SOC shutoff is probably happening by the BMS, which doesn't seem good to me.

The Victron BMV-712 can control a relay so at this point I'm sort of leaning toward using a 'dumb' power supply and having a BMV shut it down when it gets to the desired SOC that I program it to. (I would still have an overkill BMS on the battery as well)
That is exactly what I am doing with my system.

BMV-712 relay output is charge enable for: Multiplus and Orion-TR.
Victron.Connect over wireless for the MPPT Smart Solar charger.

So charging is based on State of Charge (inbound current). And since the BMV-712 is measuring the temperature of the battery, it also shuts off charging for exceeding temperature limits (overheating or freezing).

Victron gear is totally worth the money.

I am desultorily working on a Victron.Direct expander to give me more relay outputs from the BMV-712.
  • An load inhibit output to make the battery protect smarter (looking at more than battery voltage).
  • A low battery warning output based on state of charge.
  • A discharge control output I would use to drain the batteries to 30% before putting the system into long term storage. I figure a contactor relay and a small space heater would do the trick. This is a boondocking van conversion and I don't do that all the time.
I will be using an Arduino R3 plus a relay shield. If work would stop being all consuming I would already have it done. In the final weeks of launching a new product (end of March target). Dealing with failing 3rd party compliance tests (FCC). Manufacturing issues. I will be glad to get this behind me and be on to designing something new.

And working on my Van conversion.
 
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Just taking a step back here, am I correct in assuming that all of these smart chargers (other than Kisae, with limitations and the Nordkyn controller) rely on the BMS to terminate charging? That can't be right can it?
Any that allow settings should not rely on the BMS. You set the charging profile to start and stop charging just like a solar charge controller that is programmable.
 
That is exactly what I am doing with my system.

BMV-712 relay output is charge enable for: Multiplus and Orion-TR.
Victron.Connect over wireless for the MPPT Smart Solar charger.

So charging is based on State of Charge (inbound current). And since the BMV-712 is measuring the temperature of the battery, it also shuts off charging for exceeding temperature limits (overheating or freezing).

Victron gear is totally worth the money.

I am desultorily working on a Victron.Direct expander to give me more relay outputs from the BMV-712.
  • An load inhibit output to make the battery protect smarter (looking at more than battery voltage).
  • A low battery warning output based on state of charge.
  • A discharge control output I would use to drain the batteries to 30% before putting the system into long term storage. I figure a contactor relay and a small space heater would do the trick. This is a boondocking van conversion and I don't do that all the time.
I will be using an Arduino R3 plus a relay shield. If work would stop being all consuming I would already have it done. In the final weeks of launching a new product (end of March target). Dealing with failing 3rd party compliance tests (FCC). Manufacturing issues. I will be glad to get this behind me and be on to designing something new.

And working on my Van conversion.

This sounds great! Please keep us posted.
I think had I known all this going in I probably would have bought the Victron Orin and MPPT smart solar but I've already bought the Kisae DMT-1250 so I'll plan to use the BMV-712's relay to provide a +12v signal to the DMT-1250's 'control' input (For anybody with the renogy DC50S, it also has the same control input, it's called IGN+).

I don't have a lot of need for a big inverter (that may change if I decide to go with induction for cooking) so I just picked up a progressive dynamics combo load center with a built in 60A converter. I'm going to disconnect the converter from the dc fuse block and run it directly to the Kisae DMT-1250 charger so that the BMV/DMT are always doing the charging functionality regardless of whether I'm plugged into shore power, alternator, or solar.

For the post-vacation drain load I was thinking about something similar but using a de-humidifier as the load (rather than a space heater) to try to really dry the van out. I don't have your tech skills so I would just set the BMV floor to the desired storage SOC, disconnect the solar panels and then turn the dehumidifier on until shutdown occurs. Your expander certainly sounds a lot nicer though ;)
 
This sounds great! Please keep us posted.
I think had I known all this going in I probably would have bought the Victron Orin and MPPT smart solar but I've already bought the Kisae DMT-1250 so I'll plan to use the BMV-712's relay to provide a +12v signal to the DMT-1250's 'control' input (For anybody with the renogy DC50S, it also has the same control input, it's called IGN+).

I don't have a lot of need for a big inverter (that may change if I decide to go with induction for cooking) so I just picked up a progressive dynamics combo load center with a built in 60A converter. I'm going to disconnect the converter from the dc fuse block and run it directly to the Kisae DMT-1250 charger so that the BMV/DMT are always doing the charging functionality regardless of whether I'm plugged into shore power, alternator, or solar.

For the post-vacation drain load I was thinking about something similar but using a de-humidifier as the load (rather than a space heater) to try to really dry the van out. I don't have your tech skills so I would just set the BMV floor to the desired storage SOC, disconnect the solar panels and then turn the dehumidifier on until shutdown occurs. Your expander certainly sounds a lot nicer though ;)
The dehumidifier is probably a much better idea if you live in a humid climate. Humidity is not normally a problem in AZ though.

Whenever I get the mental bandwidth free to do this I will create a thread in the DIY electronics sub forum.

Pretty straightforward. The Arduino environment is basically embedded C with a lot of device drivers and callable runtime code. The executive framework is already written for you too. You have two callback functions: an init function that is called before the first call to the workloop and a workloop function that is called at a fixed, periodic rate.

The main thing missing is support for an RTOS or multiple tasks. Since Arduino is open source it should be possible to port it to FreeRTOS. I bet somebody has already done that.

Even if you don't add an RTOS, as long as you aren't trying to do more than one, hard real-time thing at a time, you can get by with a round-robin workloop. Most of my early designs used exactly that model, a round-robin workloop with interrupt driven I/O. I guess that gives you an idea how long I have been doing this (30 years now).

I can actually justify working on this since it will increase my comfort level with Arduino. My next project will be for a calibration class load cell instrument and we are using the Arduino connector scheme for our prototype ADC PCBs to simplify research. We are doing that to make it easy to evaluate a number of possible ADC solutions, but I can see value in taking the best one and turn it into a product in its own right. We will have the electronics and driver software completed relatively early in the project.
 
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My understanding is that 4S LFP is* full (100% SoC) at 13.8v / 3.45v/cell. MarineHowTo says, "The reason drop-in makers suggest such high voltages is because balancing is typically done at the top-of charge with a FET based BMS".

So maybe we could say 13.8v is enough to get a 12v LFP full but not necessarily balanced. I mention the distinction because if the proposed CV charging solution were running in parallel with solar that charged to 14.x for balancing regularly perhaps it would work ok.** Dunno. I might want <= 13.6v output to avoid holding the cells at 100% for long driving periods, still relying on solar for 14.x voltage.

-----
* or can be
** not necessarily recommending using that device, just working through the concepts for my own curiosity
I am using one of these QNBBM active balancers, 5A capable and it balances continuously at any SOC. Doesn't burn off power as heat in the process either.

If there is a affiliation link in that mess of a URL, then I am sorry. It isn't from me.

 
I am using one of these QNBBM active balancers, 5A capable and it balances continuously at any SOC. Doesn't burn off power as heat in the process either.
Thats interesting experience. Im keeping eye on such qnbbm balancer. By the way, is it really working better than the one with bunch of capacitors such as Heltec?
At one of the sites on AE they mention that 4S balancer:
Voltage Difference vs Balance Power is 1A@300mV and 3A@1V
Ive asked the seller on those but he ignored.
What I learned that on AE looks like the only balancer with constant current regardless level of voltage difference is balancing equalizer with versions 1 2 5 and 10amps but they require extra voltage of about 40-100V to power them, and are considerably expensive. They are also tunable through Bluetooth.
 
There are some great resources on grounding on the forum. Check this one out here:

Its setup that way on my SUV Works fine. I'm running Renogy dc dc charger
 
Hi HaldorEE, there's a defucnt open source arduino external voltage regulator project out there that has a lot of functions. Maybe you can borrow some code or get some ideas, maybe you already know that project: http://arduinoalternatorregulator.blogspot.com/2013/05/welcome.html
Thanks, I will look. I am a babe in the woods about Arduino so any suggestions for things of merit, I am very interested in.

Make that a babe in the woods who has been designing microcontroller based embedded systems since the early 90's. I design the PCBs then write the firmware that makes it do its tricks.

This is kinda fun, relaxing. I expected an interpreter, but this is compiled C code (GCC Gnu compiler). Pretty much all of the ARM vendor provided IDEs use the same compiler. About the only option that isn't based on GCC are Keil and IAR. They are the big boys in the embedded world. You don't get much change back from your $10K buying a full seat of either of them.
 
Thats interesting experience. Im keeping eye on such qnbbm balancer. By the way, is it really working better than the one with bunch of capacitors such as Heltec?
At one of the sites on AE they mention that 4S balancer:
Voltage Difference vs Balance Power is 1A@300mV and 3A@1V
Ive asked the seller on those but he ignored.
What I learned that on AE looks like the only balancer with constant current regardless level of voltage difference is balancing equalizer with versions 1 2 5 and 10amps but they require extra voltage of about 40-100V to power them, and are considerably expensive. They are also tunable through Bluetooth.
I have only used the passive balancer built into the Heltec BMS and now the QNBBM. I overbuilt my battery and would like to reduce the charge/discharge range to 25% to 75%. The QNBBM is the only option that I know of, that will balance at any point in the batteries SOC. If you decide to buy one, get it direct from the DeliGreen store on alibaba. I would not be surprised to start seeing fakes of this that don't really do anything, how would you know, at first.

The Chinese are masters at creating visual duplicates. When I worked in product marketing I sent a competitors product to our Chinese division to get a performance evaluation and cost estimate. They thought I wanted to order duplicates of it in volume and made a picture perfect, non-functioning duplicate of it and sent it to us.

We are like, no, that is not what we want, and DAMN, you even built all moving stuff inside. The thing had a thermal label printer and they dutifully created a perfect mockup of the print head and platen roller and label handling mechanisms, you could open it (like you do when loading new labels).

That was a serious WTF moment for all of us.
 
What DC - DC Charger options are available if my van alternator is 24v and I want to charge my 24v Lithium bank? Does Victron or anyone else make a 24v in - 24v out charger?
 
What DC - DC Charger options are available if my van alternator is 24v and I want to charge my 24v Lithium bank? Does Victron or anyone else make a 24v in - 24v out charger?
That's easy, several. Victron, Redarc, Sterling. It's when you need a step up from 12v to 24v that are harder to find.
 
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