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Jerry Work
June 30, 2022
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Lithium Batteries - 101

Important Note: There are always risks associated with being around and/or handling electricity. If you have any questions about your ability to handle these risks safely, please do not attempt to follow any of what I have outlined below and instead, hire a licensed professional to do this for you. I am only sharing what I have done. Neither I nor Bus Conversion Magazine assumes any liability for what you do or how you do it.

Here are nine things you need to keep in mind as you think about upgrading your RV/bus electrical system to include LiFePO4 (lithium iron phosphate) batteries.

1.) You cannot directly connect lead-acid batteries (whether they are called flooded, gel, AGM, or sealed lead-acid) to LiFePO4 (lithium) batteries because they operate at two diferent voltage levels. The higher voltage of the LiFePO4 batteries would try to bring the lower voltage lead-acid batteries up to the same level as the lithium batteries which could cause a large and potentially dangerous inrush of current.

2.) You need a device called a battery-to-battery (BtoB) charger to recharge your new lithium batteries at the proper charge level and profile from the same alternator (your existing one) currently used to recharge your existing lead-acid starting/house batteries. The BtoB charger “fools” the alternator into thinking the lead-acid starting/house battery is not yet fully charged so it tells the alternator to keep putting out charge current even after the lead-acid start/house battery is fully charged.

The BtoB charger changes the output profile to a charge profile required to fully charge the lithium batteries. When they become fully charged, the BtoB charger tells the alternator to decrease or to shut off the current to the lithium batteries, and/or the battery BMS shuts of the battery. The BtoB charger will then see the starting battery as being fully charged and turn down or turn of the alternator. The BtoB charger will also isolate the starting battery from the house battery bank(s) so the lead-acid and the lithium batteries are never connected directly to one another.

The newest alternators used in some vans and pickups put out variable voltage to gain some additional fuel mileage and some may also use regenerative braking to shut of the alternator while applying the brakes so you will need a compatible battery-to-battery charger for those.

3.) Do not connect your existing alternator directly to lithium batteries. The BMS controlling the lithium batteries will shut of the batteries when they become fully recharged. If the alternator is still producing power, it could cause a large voltage spike that could be dangerous to you and or your coach electronics.

You can install a device made for absorbing that voltage spike or you can leave one or more lead-acid batteries in your system, keep your existing alternator connected to those lead-acid starting/chassis batteries and install a battery-to-battery charger to provide the correct charge profile to your lithium batteries.

If the BMS shuts off the lithium batteries, the lead-acid batteries have so much internal resistance they will absorb any voltage spike without harm. And, the battery-to-battery charger will limit the amperage draw from your alternator to keep from burning it up trying to recharge the lithium batteries at the amperage rates they could potentially draw if directly connected to your exiting alternator.

4.) Do not directly connect lithium batteries from two diferent suppliers because they each have their own battery management system (BMS) and one could fight with the other under some circumstances.

5.) You can usually connect multiple lithium batteries of the same model and capacity from the same supplier in parallel with one another to achieve higher capacities, but check with the supplier to see what the limits are.

6.) You can connect two or more battery chargers from the same manufacturer in parallel if you want faster charging.

7.) Lithium batteries in an RV or bus conversion can get recharged from the engine alternator using appropriate electronics (like the B to B charger discussed above), from shore or generator power using a 120VAC battery charger that has the proper lithium charge profiles built-in, or from solar panels using an MMPT solar charge controller that has the proper lithium charge profiles built-in. Often the 120VAC battery charger will be combined with an inverter so it can provide both functions.

8.) If you have diferent battery banks made up of both lead-acid and lithium batteries, and/or different kinds of lithium batteries, you need to be sure the components you select to recharge them from the engine alternator, from shore, or generator power, or from solar panels are compatible.

9.) Battery cables have resistance and the smaller they are the more resistance they have. The greater the resistance, the more DC voltage will drop as it travels through the cables. You must size the battery cables and fuses to the amp carrying capacity required for the types and sizes of battery banks you wish to employ and the loads to which they will be subjected.

Don’t scrimp on cables. When in doubt, use larger and better-quality cables. The ones with very high strand count and silicone insulation (usually called marine battery cables) can carry more amps than automotive battery cables or welding cables of the same size.

Avoid cables called CCA as those are simply copper-coated aluminum and usually can carry far lower amp loads than real battery cables. And finally, keep your cables as short as possible as longer cables mean more resistance and therefore more voltage drop.

Keep these things in mind as you think about upgrading your RV/bus electrical system to include LiFePO4 (lithium iron phosphate) batteries and you will be just fine.

Article written by Jerry Work

Jerry Work spent his professional career in technology management, first as the founder and CEO of two moderate-sized computer software companies and then as the Associate Laboratory Director for the Pacific Northwest National Laboratory (PNNL), one of the DOE multi-program laboratories. At PNNL, in addition to overall Laboratory management, he oversaw the laboratory’s work in the energy, transportation, medical and information technologies.

After retirement, he and his wife Sharon purchased a Beaver Patriot motorhome and began a cold turkey four years of full-timing which they enjoyed greatly. They then purchased a 1907 former Masonic Temple in rural Southern Oregon, restored the building and remodeled it into his studio and gallery on the first floor and living quarters on the second floor. There he designs and handcrafts fine furniture. He is well known for his many articles and tutorials about how to get the most from Festool and other-high end woodworking products.

They purchased the first of what became two fully restored GMC motorhomes, those iconic and swoopy front-wheel drive units from the 1970’s. They found the second of their two GMC’s in an air-conditioned building in Naples, FL, with just 11,000 miles on the clock following a ground-up restoration in 1984. Both of those motorhomes found their way from Mexico to Alaska and from the West to the East coast. He wrote extensively about his experiences with GMC’s and gave many a presentation at GMC club events over the years.

A few years ago they decided to go back out on the road again for longer periods of time than they could support in the GMC motorhomes so purchased a low mileage 1997 40 foot Country Coach Prevost bus conversion which is now home for more than six months out of the year. Visitors always welcome no matter where in their travels is their motto.

You can reach Jerry Work by email at:
GLwork@mac.com

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