another DIY roadtrek lithium - newb needs help

[booster]

Originally Posted by rowiebowie

I once depleated my lithium coach batteries to BMS cutoff. They would no longer charge from an ac source (house current or generator), but charged up just fine from my engine alternator through my Renogy 40A DC to DC charger.

Perhaps the main factor in my situation is the ignition wire that runs to my DC to DC. It is the same one that ran to my original battery separator that is now bypassed as a result of my lithium upgrade. This "ignition wire" is a very small gauge wire, probably only 18ga tops.

Is the Renogy output connected to the starting battery in any way other the the ignition wire? You are on a single alternator, so that would expected to be running with output, but I am surprised the Renogy would turn on the output without seeing a battery voltage on the output side or at least a battery sense small voltage control wire to the coach batteries. It would be very interesting to see what voltage the Renogy was running at under the initial power up before the batteries came back on line as it would have no reference on that side.


Just found the answer, at least for Renogy and Renogy BMS. Don't know if this would apply to other BMS and battery setups or not.

The DC-DC have reactivation feature to awaken a sleeping lithium battery. The protection
circuit of Lithium batteries will typically turn the battery off and make it unusable if over-dis-
charged. This can happen when storing a Lithium pack in a discharged state for any length
of time as self-discharge would gradually deplete the remaining charge. Without the
wake-up feature to reactivate and recharge batteries, these batteries would become unser-
viceable and the packs would be discarded. A small charge current will be applied to the
house battery to activate the protection circuit and if a correct cell voltage can be reached,
it starts a normal charge.

I am pretty sure that davydd had to push and hold a button on his first ARV to get the reactivation to happen so the rest of the system would see voltage.



Of course if the BMS is in cold/hot shutoff it would not be activated by the Renogy recovery method.

[bumpersignal]

I’m just wondering if even thinking about that is premature optimization. I’ve depleted my agms before yet the stand-alone alternator for some reason still got “excited” to charge them automatically. Or maybe it was because I had multiple batteries they don’t all deplete down to exact zero? And maybe that’s the answer I need to use by installing more than one lithium battery.

[rowiebowie]

I think some of this discussion is getting into the weeds. I can't speak for a second dedicated alternator. But for a single OEM alternator, the wiring for a DC to DC charger is straight forward and nothing to worry about.

Your DC to DC will (according to your model and alternator) either wake up automatically from your engine alternator or (in my case) from the engine ignition wire. My Renogy DC to DC included instructions for either case.

[rowiebowie]

Originally Posted by booster

Is the Renogy output connected to the starting battery in any way other the the ignition wire? You are on a single alternator, so that would expected to be running with output, but I am surprised the Renogy would turn on the output without seeing a battery voltage on the output side or at least a battery sense small voltage control wire to the coach batteries. It would be very interesting to see what voltage the Renogy was running at under the initial power up before the batteries came back on line as it would have no reference on that side.


Just found the answer, at least for Renogy and Renogy BMS. Don't know if this would apply to other BMS and battery setups or not.


I am pretty sure that davydd had to push and hold a button on his first ARV to get the reactivation to happen so the rest of the system would see voltage.


Of course if the BMS is in cold/hot shutoff it would not be activated by the Renogy recovery method.

Since I don't always know enough to be concerned with why things work, ignorance is often bliss.

But allow me to clarify. I stated earlier that my battery BMS had cut off when I don't know this to be the case. All I know is my Renogy Inverter charger did not sense enought battery voltage to charge from an ac power source when my DC to DC did.

I don't think it was the BMS after all as I seem to recall a voltage reading of 10 volts or there about on my battery monitor. Sorry for the confusion.

[bumpersignal]

Originally Posted by larrylwill

Well they told me most people send in there alternator and they will add the balmar. I said I guess it will be around $99 and they said yes. I didn't pursue further. I'm not going that way. Ill buy a 2nd BMS first.

I stand corrected I’m so glad you were right about this. The $400 cost from nations to convert the alternator also includes the balmar device and harness! Which turns out to be a fantastic deal imo and a no brainer for me. I’m going to go that route

[larrylwill]

Quote:
Originally Posted by larrylwill View Post
Well they told me most people send in there alternator and they will add the balmar. I said I guess it will be around $99 and they said yes. I didn't pursue further. I'm not going that way. Ill buy a 2nd BMS first.

I stand corrected I’m so glad you were right about this. The $400 cost from nations to convert the alternator also includes the balmar device and harness! Which turns out to be a fantastic deal imo and a no brainer for me. I’m going to go that route

My original Post said $99 but was a typo should have been $400 same key. I didn't know it included the harness but good to know. good luck.

[larrylwill]

I finally got everything working. I bought a 12V timer module off Ebay $6.00. I mounted it with the battery charger, ac switch, inverter inside the original inverter cabinet. I then ran a wire from the starter selenide key switch to the module trigger input. Another wire from the house battery to the 12v input of the module, another wire from the module relay 12v output to the dc2dc inverter input as well as the dc2dc power on wire. I found that a 4 sec delay works well. Now when I start the engine it triggers the module for 4 sec which is enough to excite the inverter which then charges the battery through the dc2dc until I turn the engine off.