My Interstate Lithium Battery Adventures

[lewster]

Originally Posted by LB_3

Awesome! Now I have a new tool to add to my limited electronics inventory.

Ok sparkies, my next big electronics hurdle is how to throttle the power from the alternator. Lithium batteries can accept hundreds of amps and alternators have no inherent current limits which could spell disaster. I really don't want to melt my alternator, weld the battery isolation switch closed, or start a fire. I think the power cable is only 4awg so I can probably get 50 amps through it safely if I can't route a larger cable.

I thought about trying to reappropriate my current PWM solar charge controller but it's only rated for 30 amps and it's designed more as a voltage regulator than a current limiting device.

So far the only things I've seen that can do this that aren't space heaters are DC motor controllers and some PWM circuits built by the quacks in the HHO community. Seriously, go to a search for HHO controller and tell me we can't become billionaires selling Brawndo to the masses.

Look to the marine industry. Victron makes DC to DC converters and Balmar makes battery charge regulators specifically for alternators.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
ABYC Certified Master Marine Electrician
Master Tech Energy Systems, Inc.
AM Solar Certified Installations
Lifeline AGM Batteries**Magnum Inverters***Victron Energy Components
541-490-6357

[LB_3]

Looks like Roadtrek employed some pretty good engineers. Now they just need to hire some better interior designers and cabinet makers.

[LB_3]

Thanks again Lew!

[InterBlog]

Originally Posted by GenXair

Hi LB_3,

Please take lots of photos or videos of your install.

We will. I'll also be fashioning a series of blog posts on it, similar to what I did for our solar install, but perhaps in more detail. I try to find the sweet spots of supplying people with good information while at the same time not overloading with a lot of info on builds that we might be the only Class B owners on earth to undertake.

[amirm]

Originally Posted by LB_3

Looks like Roadtrek employed some pretty good engineers. Now they just need to hire some better interior designers and cabinet makers.

Seems to me, it is easier for us to duplicate their electrical system in our Interstates than trying to fit our nice furnishings, in their unit.

I am trying to nail down the components they used and then figure out one to stuff it all in our units.

[LB_3]

It looks like they used GBS battery cells in their battery box.

The alternator regulator looks like it might be this device: http://www.defender.com/pdf/ARS-5.pdf

[Boxster1971]

Originally Posted by LB_3

It looks like they used GBS battery cells in their battery box.

The alternator regulator looks like it might be this device: http://www.defender.com/pdf/ARS-5.pdf

Agree that is a Balmar regulator, he says so in the video. Not sure which model. But look closer at the top of those batteries. They look more like one of the CALB brands as seen at bottom of this web page.
http://www.ev-propulsion.com/battery-choices.html

The GBS batteries all have the unique four screw connections.


- - Mike
2013 Lounge EXT on 2012 Sprinter

[LB_3]

I only noticed the light blue color. I didn't realize that CALB had any color but grey.

[Boxster1971]

Originally Posted by LB_3

I only noticed the light blue color. I didn't realize that CALB had any color but grey.

The grey CALB cells are their CA series. They actually make four different lithium battery series/models. I took a closer look at the video on my 24" desktop monitor. Those sure look like CALB SE200 cells, which makes sense because Roadtrek say their battery is a 200AH. So four SE200 cells in a box plus the electronics on one end make the Roadtrek battery.

See detail of CALB SE200 here...
http://www.evlithium.com/CALB_Battery/42.html

...and here...
http://en.calb.cn/product/show/?id-648


- - Mike
2013 Lounge EXT on 2012 Sprinter

[amirm]

On the alternator upgrade, the charge controllers require access to the field winding of the alternator for their operation. That would be easy to implement using a secondary alternator. Did some searching and seems that without getting that as a factory option from Mercedes, it is more difficult retrofit with new bracket, belt, clearance, etc. Wonder if Roadtrek has the secondary alternator option. I had a secondary alternator in my boat and it worked great this way.

I think the current alternator is rated at 220 amps which is not bad. Not sure what it puts out at idle though. High performance ones can generate 200 amps at idle. The issue per above becomes how to control their output. The alternator needs to simultaneously drive the engine needs and our charging. Turning it off and such is not going to be in the cards using external charge controller.

The Lithium battery needs to be isolated from the engine or it will attempt to charge/over charge that battery. The current BIM may also get confused anyway due to that differential (I have not looked).

Easiest fix would be a DC-to-DC converter that is dedicated to charging the Lithium from the alternator output. The worry there is find space for a high-current one. There will also be some power loss.

Anyone can see clear to a good solution here? Sure would be nice to be able to charge the battery bank using the engine instead of the loud generator.

[Boxster1971]

Just read something surprising about those Roadtrek lithium battery modules - they apparently have a large internal parasitic drain. It was reported to be 6 amps on this B-van forum post which originated from one of the Roadtrek owners Facebook pages.
http://www.classbforum.com/forums/f5...amps-5549.html

Now that is just crazy.... And we think the Interstate has problems killing batteries.


- - Mike
2013 Lounge EXT on 2012 Sprinter

[amirm]

Originally Posted by LB_3

So, finally we get to the fun part. I have chosen the following BMS, the SBMS-100:

First, a belated thank you for creating this thread and doing so much of the legwork .

I contacted Dacian and he said he is building a batch for next week. So I put in my order for the SBMS-100. I have also been studying this approach. Summarizing the benefit of this controller is that it is a super low cost way to get a solar charger controller and Lithium Battery Management System in one unit. At just $260, it is a real bargain as the BMS alone is likely to cost a lot more than this.

Some items to consider though:
1. As a stock item, SBMS-100 can only handle 120 amps. So only a 1000 watt inverter can be supported. An external shunt and relay enables support for up to 500 amps. That takes care of measurement. But I am unclear how load connect/disconnect works. Yes there is an output to shut down the inverter but how about 12 volt loads? Surely they need a relay to disconnect them too.

2. The unit will need a heatsink to keep it cool enough to handle our application.

3. I am worried about the quiescent power consumption with WiFi and such. Hopefully there is a low power mode in there when one is not using the inverter and such.

Anyway, just thinking out loud.

[Boxster1971]

I also just read something interesting over on the Roadtrek Facebook page when searching for more info on the Etrek.

https://www.facebook.com/groups/road...2165389942444/

It was a post by Jim Hammill, president of Roadtrek, here is what he said.
=================
"Every three months I get another person calling me telling me they burnt their RV up trying to make a home E-Trek.

Simply put, a list of parts and a tool box do not constitute an Etrek.

Its not LEGO.

I have written this several times and I will do so again. The installation and engineering of the Ecotrek technology, which would include larger scale battery systems (AGM or LiFPO), engine generators, solar, new inversion, etc, are a SYSTEM. it is not a "plug and play" type technology. There are huge power draws and the safety of such a system is what I do for a living. Don't go there.

DO NOT ATTEMPT TO BUILD A SYSTEM ON YOUR OWN. if you are an electrical engineer, or you have one stamp your plan and inspect it when you are done, then maybe. But folks, this stuff is fine when done right, and deadly when done by people who think they know.

And yes, this applies to people adding multiple batteries. If those get low, the voltage drop can cause a massive Amp spike. Thats a Fire. Don't do it.

And don't put batteries inside your coach. Ever. Hereendeth the lecture."
==================

This is good advice if you don't have the technical background and skills to pull off some of the mods we have talked about in the forum. This stuff is dangerous and you can get hurt or damage your rig. Be careful!!


- - Mike
2013 Lounge EXT on 2012 Sprinter

[amirm]

While I don't believe this line, "Every three months I get another person calling me telling me they burnt their RV up trying to make a home E-Trek" the larger point is of course is sound. So far, until we figure out a complete formula there is way too much complexity for wholesale changes of the system. And the high-current dangers ever present.

[LB_3]

I didn't expect this thread to advance so quickly so I'll post some more of my recent adventures.

Originally Posted by amirm

Some items to consider though:
1. As a stock item, SBMS-100 can only handle 120 amps. So only a 1000 watt inverter can be supported. An external shunt and relay enables support for up to 500 amps. That takes care of measurement. But I am unclear how load connect/disconnect works. Yes there is an output to shut down the inverter but how about 12 volt loads? Surely they need a relay to disconnect them too.

The SBMS-100 has 20 IO pins on the left side. 2 are reserved for measuring an external shunt to keep track of external loads like a big inverter. And the 3.3v pin out I discussed for controlling the external inverter earlier is really intended to control all the external loads. It just needs to signal a (solid state?) relay if 100 Amps of DC is not enough.

2. The unit will need a heatsink to keep it cool enough to handle our application.

I have this one worked out already. :-)

We don't use our radio/dvd player in the back of our IA so I plan to remove this little space heater and have a custom panel water jetted:


So for a heatsink, I purchased the following 90mm heatsink:
http://www.luxeonstar.com/90mm-squar...lpha-heat-sink
I then trimmed it down from 90mm x 90mm to 85mm x75mm using an air powered reciprocating saw. Next I downloaded the circuit board cad files, and printed out a copy of the main board so I could use it as a template for drilling the mounting holes:

I replaced the existing screws with 16mm M3 screws from Home Depot but they're really too short so I purchased a few more from ebay and am waiting for them to arrive.

The 90x90 heatsink was rated at 1.7degrees C per watt. Now that I've cut it down, to 85x75, I estimate it is now about 2.0 degrees C per watt. I'll save you some math but the resistance on the charging path is 0.0024 Ohms and on the load side it's 0.001 Ohms. I don't expect to see anywhere near 100 amps on the charging side give alternator limits discussed previously and only 300 watts (for now) of solar.

I estimate, based on a warm ambient temperature, I can probably dissipate 16 watts total which should be good for 100A of loads and 80 amps charging which should be impossible to achieve with an externally connected inverter.

I'm not entirely sure I'll even need this heat sink if the custom panel I have water jetted is aluminum. BigBlueSaw.com quotes one of their 8"x12" demo panels designs at $103 when cut out of .25" 6061 aluminum.

I would probably make a fit check unit from acrylic for about $35 first but if I use a big slab of aluminum, I may not even need my current heat sink, particularly if I choose not to run any loads through the SBMS and use the solid state relay I mentioned in a another thread.

I like rotary switches so I will probably use something like this to control the load to the inverter relay, but hopefully with a different knob:

I contacted the manufacturer a few weeks ago and they sent me their panel design guide so I have the cut out dimensions.

As a pilot, I'm familiar with thermal breakers by the dozens so I'm thinking of using these instead of blade fuses:

form Del City: http://www.delcity.net/store/Thermal...akers/p_539615

Is there any reason not to use thermal breakers? My DC panel will likely go in the top of the closet where I currently have a few switches connected to some DC/DC converters. I expect this to eventually be a mass of knobs, thermal breakers, and lcd current meters.

3. I am worried about the quiescent power consumption with WiFi and such. Hopefully there is a low power mode in there when one is not using the inverter and such.

Anyway, just thinking out loud.

There is a low power mode. The wifi can also be turned off if you like but it really doesn't draw much power from my limited testing. I have the wifi off right now and it says that it's drawing less than .03 amps from a 5 volt USB cable.
I haven't hooked a meter up to it so I can't verify it's internal reading.

In interest of full disclosure, the SBMS has a few minor issues. One is that if you place a fuse or disconnect on the Batt+ line and if opens, it will try to draw power for the loads through the cell monitoring/balancing pins and damage the BMS. This means you need a bulletproof cable between the BMS and battery. But overcurrent protection can be provided on individual loads or even on the battery negative so while this is an obstacle, it's not insurmountable. Of course if all your loads are controlled through an external relay, there will not be any need to connect loads directly to the SBMS.

Another limitation is that the wifi is read only. The SBMS configuration settings can not be manipulated from a handset with the current software so the SBMS will need to be mounted somewhere accessible. Perhaps Dacian or one of his customers will one day add a remote config capability. I'm only a half decent visual basic programmer so I'm probably not the right person to jump into that code. As currently implemented the HTML file can't be easily loaded from Apple iOS so Android may be your friend for a while. I have loaded the proper html on my iphone and accessed the data on the SBMS but it was quite cumbersome. If I ever get past my current project list, I may tackle that issue.

AM SOLAR has been selling a complete system from Victron Energy that would be much more plug an play but they're currently sold out. Besides, if all I ever do is work on the RV installing other people's stuff, I'm going to start viewing the RV as more of a job and I've already got one of those. This is fun for me since I'm not very good with electronics and its proving to be a fun learning curve to climb. :-P.

[LB_3]

Tomorrow, I'll post the ribbon cable connector part numbers and breakout boards I've purchased after work and start a discussion on battery sourcing which is a much more complicated topic than it should be.

[amirm]

Thanks for the explanation. I am not clear about something though. I thought you were going to use a 2 Kw inverter. If so, you are going to have a load > 200 amps, not 100.

As to using breakers instead of fuse, that may not be wise depending on what is being protected. Fuses are ultra fast compared to those thermal breakers/switches. They are fine for protecting wires and such. But for electronics, much more damage will be done compared to a fuse. And if the equipment requires a fuse and you use a breaker, there can be a risk of fire.

Breakers can be useful if you think they are going to trip often. I don't expect any of the current fuses to blow in normal operation so that benefit is not needed.

[LB_3]

The 2000w inverter will be connected directly to the battery. I will use a shunt to track the current draw and the IO interface on the SBMS to turn the inverter on and off. This is what I mean by external loads. Versus internal loads passed through the SBMS. In the Etrek video they had two positive cables. One for charging, the other for loads. Not much different from what I described above.

[LB_3]

I'll skip the thermal breakers and use panel mount fuses instead. I've already picked them out as well. :-)

[InterBlog]

Originally Posted by Boxster1971

...

"Every three months I get another person calling me telling me they burnt their RV up trying to make a home E-Trek."
...

I have no doubt whatsoever that some people do this. However, what has to be put into perspective is that the equipment in there may not be that great to start with. A few months ago, we almost had our RV burn up because the almost-new electrical converter short-circuited, an event that the manufacturer admitted was entirely the fault of their product, not our usage. Here's the Air Forums thread on that one. No comments on it... I'm not sure what there is to stay about it. It is what it is. But we then found out that the equipment they supplied as a warranty replacement is not doing what it's supposed to be doing. Given this dramatic and difficult history, at this point I don't feel like we will be trading out some kind of "sure thing" for a riskier configuration.

ADVISORY - Electrical converter failure hazards