HowTo Fabricate Portable Power and charge from your MME

[dtbaker61]

Just wanted to post a couple pix of my 'mid-size' Portable power unit... 2kWhr of Lithium battery, 3000watt pure sine inverter, and a custom cord are all you need to keep it charged from your MME by accessing the 12v connection points for 'extended use' or re-charging when you need to, and then roll the unit away from the vehicle to wherever you need power.

This 'larger' unit can handle peak loads over 3000 watts, but really intended for average loads for a couple hundred watts.... which is enough to run all the basics in a house, including the refrigerator, in a pinch. Backed up by a MME, it could run for DAYS if the Grid is down. Or, you can use separate solar panels to recharge and treat it as a nano-grid to energize a home, campsite, or job site.

I have done a couple of the smaller units (1kWhrbattery and 1500watt inverter) that fit in a carry on which drops neatly into the Frunk, and is a lot easier to lift and transport....

The 'charge' cable from MME 12v doesn't need to be very big as current is naturally limited by the relatively small voltage difference between auto at 14.4v and (loaded/depleted) portable batteries than might sag down to 12.0.

I mostly just wanted to share the idea with MME Owners so you are aware you have the perfect 'emergency backup' energy stored up in your MME!

 

[DaMeatMan]

Just wanted to post a couple pix of my 'mid-size' Portable power unit... 2kWhr of Lithium battery, 3000watt pure sine inverter, and a custom cord are all you need to keep it charged from your MME by accessing the 12v connection points for 'extended use' or re-charging when you need to, and then roll the unit away from the vehicle to wherever you need power.

This 'larger' unit can handle peak loads over 3000 watts, but really intended for average loads for a couple hundred watts.... which is enough to run all the basics in a house, including the refrigerator, in a pinch. Backed up by a MME, it could run for DAYS if the Grid is down. Or, you can use separate solar panels to recharge and treat it as a nano-grid to energize a home, campsite, or job site.

I have done a couple of the smaller units (1kWhrbattery and 1500watt inverter) that fit in a carry on which drops neatly into the Frunk, and is a lot easier to lift and transport....

The 'charge' cable from MME 12v doesn't need to be very big as current is naturally limited by the relatively small voltage difference between auto at 14.4v and (loaded/depleted) portable batteries than might sag down to 12.0.

I mostly just wanted to share the idea with MME Owners so you are aware you have the perfect 'emergency backup' energy stored up in your MME!

Nice build! Be careful with those suicide cables though particularly if you intend on backfeeding into a 15a - 20a household outlet! One of them appears to be hard wired to the output of your inverter, and is essentially just a live dangling 120v output. Yikes!

I too have built several custom lithium battery banks, the largest one (center in picture) being a 7S 24P 84Ah 2.175 Kwh battery with a 2000W (constant) and 4000W surge pure sinewave inverter, as well as a built-in in MPPT solar charger at up to 15A. It also has a dedicated lower current DC to DC buck boost converter that is suited to safely pull approximately 100W from a standard vehicle cigarette lighter outlet so as not to blow the vehicles fuse. I've also considered taping directly into the MME's low voltage battery to keep the pack topped up in a longer term usage situation, but you would really want to keep the demands on the LVB below 10A - 20A to ensure you don't end up depleting or damaging that battery. At that current your essentially just trickle charging though, and you would want to keep your loads below 200W overall to ensure it's sustainable.

Anyway if anyone is interested you can find my YouTube channel here where I went through some of the smaller builds as well.

https://youtube.com/user/joecmarques

 

[dtbaker61]

Nice build! Be careful with those suicide cables though particularly if you intend on backfeeding into a 15a - 20a household outlet! One of them appears to be hard wired to the output of your inverter, and is essentially just a live dangling 120v output. Yikes!

I too have built several custom lithium battery banks, the largest one (center in picture) being a 7S 24P 84Ah 2.175 Kwh battery with a 2000W (constant) and 4000W surge pure sinewave inverter, as well as a built-in in MPPT solar charger at up to 15A. It also has a dedicated lower current DC to DC buck boost converter that is suited to safely pull approximately 100W from a standard vehicle cigarette lighter outlet so as not to blow the vehicles fuse. I've also considered taping directly into the MME's low voltage battery to keep the pack topped up in a longer term usage situation, but you would really want to keep the demands on the LVB below 10A - 20A to ensure you don't end up depleting or damaging that battery. At that current your essentially just trickle charging though, and you would want to keep your loads below 200W overall to ensure it's sustainable.

Anyway if anyone is interested you can find my YouTube channel here where I went through some of the smaller builds as well.

https://youtube.com/user/joecmarques

very nice job on your PowerBoxes! It's a balance between cost, space, and expected use for sure.... My goal was to come up with the least expensive way possible to extract enough power from the MME to be an effective home backup system in case of Grid Outage.

I hesitate at using 'suicide cords' for backfeed, but do go to great lengths to educate users to minimize exposure to live prongs. The reason I even add the 120v->240v backfeed cord is that it is the easiest way to power both legs of a typical home service IF there is a 240v outlet available.... and many EV owners do have 240v outlets rather than hard-wired EVSE.

The inverter I use a lot has two 15amp 120v outlets and a terminal block that can put out 30amps 120v.... and since I wire it thru a 240v plug, it energizes both legs at 120v, but they are 'in-phase', so cannot provide 240v or run 240v appliances; which you wouldn't want to do in Emergency situations anyway. The plug is 'holstered' in an un-connected outlet on the side just so that the energized prongs are never exposed.... I could have used a plug end with 'protected' prongs, but the cost goes up considerably.

 

[fleeps]

Way cool! If i understand correctly, the MME slowly charges the extra battery. The extra battery provides surge capacity to handle, say, cooking, for a short time (depending on the size of this battery). But for the longer term, expected use is low enough that the connection to the MME at the battery terminals can keep up. Is that correct? What if the demand is too high for too long?

 

[JohnFoxeSheets]

Way cool! If i understand correctly, the MME slowly charges the extra battery. The extra battery provides surge capacity to handle, say, cooking, for a short time (depending on the size of this battery). But for the longer term, expected use is low enough that the connection to the MME at the battery terminals can keep up. Is that correct? What if the demand is too high for too long?

If demand is too high for too long then you drain the extra battery. If you've designed your system properly, that's about all that happens - the car will continue to try to charge your extra battery, but if your drain is higher than the recharge rate of the battery, then it won't be able to keep up and you could ultimately damage the extra battery. But as long as the system doesn't draw more current than the Mach E can handle, it shouldn't damage your car. But, it's complicated and stuff can go wrong. So it's best to be quite conservative with your loads (both the wattage and the watt-hours).

 

[dtbaker61]

Way cool! If i understand correctly, the MME slowly charges the extra battery. The extra battery provides surge capacity to handle, say, cooking, for a short time (depending on the size of this battery). But for the longer term, expected use is low enough that the connection to the MME at the battery terminals can keep up. Is that correct? What if the demand is too high for too long?

not exactly.

the extra battery is not needed at all if exporting directly from MME as long as the load is <160a x 12v = 1900watts. The MME on-board converter can keep up with that.

A 'buffer' battery is needed when the MME is not available or not within reach of the load. The buffer battery could be 12vDC -48vDC depending what inverter you want to use.... In this case the MME becomes a 'charger' rather than running loads directly.

if its a 12v system for small loads <2000w, then 'fast charging' doesn't even need a charge controller, you can just jumper from MME 12v connection points to external 12v battery(s), and they will charge at a current determined by the voltage difference.... up to 100amps if the external battery is down to 12.0 volts, so you have to use heavy cables.

in some cases I've used the MME to pull from 12v connections, run a 1500w inverter/charger, and charge an external 48v system. So the load on the MME is never more than 1500 watts, and the larger 48v 'house' system can handle full household loads while charging batteries at a steady rate that the MME can handle for export

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