Lithium and DC-DC Charger?

[Ramblin__Ralph]

My two group 27 lead acid batteries need replacing. Even though I'm too old to get maximum benefit from lithium longevity, I am thinking about going with a single 100 AH LifePO4 lithium. Doing some research it appears that a DC - DC charger is needed between the truck alternator and camper battery to protect the alternator. Would this still be required with only one 100 AH battery? Truck is a 2006 GMC 2500HD. Also have 125w of solar.

Thanks,
Ralph

[theoldwizard1]

toddb wrote:
I went without vehicle charging for when I switched over, I only used solar. No problems until the fridge upgrade.
I use a small one now on factory wiring and would recommend it if you want vehicle charging.

Interesting point you bring up.

First, everyone needs to understand that DC compressor refrigerators actually have an inverter inside. They will shutdown at some pre-determined minimum voltage. You need to verify that yours will automatically restart.

Second, of your goal is to MAINTAIN your battery bank voltage, NOT RE-CHARGE a depleted bank, then you probably do not nee a DC-DC charger. Simply connecting you RVs battery to the starting battery connection at your 7 way, is probably adequate !

ONE EXCEPTION ! If you are running a 120VAC refrigerator from an inverter, will your inverter automatically re-start after a temporary low voltage event or do you have to press a button/flip a switch ? If YES, you want a DC-DC charger (because it will maintain proper battery voltage at all times the engine is running).

[theoldwizard1]

ticki2 wrote:
This is probably a dumb question , forgive my ignorance . I have been reading about these new technology batteries , lithium and now Sio2 that can be discharged to 80 and 100 percent . How do they power equipment that requires 12v to operate like a furnace sail switch , at this state of DOD ?

It depends on the equipment.

Most inverters will shutdown somewhere between 10V and 11V. Things like light (both incandescent and LED) will keep running below 10V. USB Chargers ?

[theoldwizard1]

duplicate

[theoldwizard1]

pianotuna wrote:
Hi,

Try SiO2 100 amp-hours for about 50% of the cost.

https://azimuthsolarproducts.com/product/12v-100ah-sio2-battery/

No need for a dc to dc charger.

I don't understand how you can say that ! Straight from the product page

Azimuth Solar Products wrote:
Settings for your SiO2 battery if you are choosing custom programming on your charge controller:
Equalizing Voltage -> 14.6 or Shut off this function if available
Boost Voltage -> 14.6
Floating Charge Voltage -> 13.6

You will likely NEVER be able to achieve those voltages without a DC-DC charger !

[theoldwizard1]

Ramblin' Ralph wrote:
I am thinking about going with a single 100 AH LifePO4 lithium.

The size of your RC battery bank depends on how much power you draw and for how long. Your pair of Group 2y batteries and deliver about 160 Ah. Is 100 Ah going to be adequate ? Only you know the answer.

Ramblin' Ralph wrote:
Doing some research it appears that a DC - DC charger is needed between the truck alternator and camper battery to protect the alternator.

Not exactly true. A DC-DC chargers does two jobs. It PROPERLY FULLY CHARGES your RV battery while you are driving and it isolates the RV from the engine starting battery so that the RV battery can not be drained by the vehicle (some DC-DC chargers have a temporary bypass to emergency engine starting).

Ramblin' Ralph wrote:
Also have 125w of solar.

If your solar is working well, my guess is one 100Ah lithium battery would be adequate.

[time2roll]

Ramblin' Ralph wrote:
Thanks for the input. My “protect the alternator” question was because of the following video I saw from Victron. Evidently the lithiums can put a higher amp load on the alternator. In their lab study one of them started smoking because of insufficient cooling while charging a 300 AH lithium.
Video here

I was just checking to see if I might have the same problem with a single 100 AH. Thanks for the tip on the SiO2 batteries. I'll look into them.

Ralph

Not just the size of the battery but the size and length of the wire connecting the battery. I speculate the boat had relatively fat and short wire to reduce voltage drop to the previous lead acid batteries.

[Ramblin__Ralph]

Thanks for the input. My “protect the alternator” question was because of the following video I saw from Victron. Evidently the lithiums can put a higher amp load on the alternator. In their lab study one of them started smoking because of insufficient cooling while charging a 300 AH lithium.
Video here

I was just checking to see if I might have the same problem with a single 100 AH. Thanks for the tip on the SiO2 batteries. I'll look into them.

Ralph

[toddb]

I use a victron 12/12 9, I think it's 120W so about the equivalent of 1 panel. The truck may be 10ga, hard to tell but I think in the camper and umbilical were 12 so this model is plenty safe. I get 7-7.5A out of it at 14.6V.

[NRALIFR]

Todd, just out of curiosity what size DC-DC charger were you able to run using the factory wiring? I know that’s typically called a 30 amp circuit, but I kinda doubt it can do 30 amps for long. Even a small DC charger could out perform solar though, unless you have a really big system.

:):)

[toddb]

I went without vehicle charging for when I switched over, I only used solar. No problems until the fridge upgrade.
I use a small one now on factory wiring and would recommend it if you want vehicle charging. This will keep the voltage stable as you don't want the BMS to disconnect on over or under voltage from the alt.

[srschang]

ticki2 wrote:
This is probably a dumb question , forgive my ignorance . I have been reading about these new technology batteries , lithium and now Sio2 that can be discharged to 80 and 100 percent . How do they power equipment that requires 12v to operate like a furnace sail switch , at this state of DOD ?

The voltage curve on a lithium battery is way different then a lead acid. The lead acid voltage drops steadily as the charge is depleted. The lithium voltage stays virtually level throughout the discharge, then drops off a cliff when the battery is near completely discharged. That's why a volt meter works well on a lead acid battery to measure the charge, but on a lithium a voltage measurement won't help determine state of charge.

[jaycocreek]

pianotuna wrote:
Hi,

Try SiO2 100 amp-hours for about 50% of the cost.

https://azimuthsolarproducts.com/product/12v-100ah-sio2-battery/

No need for a dc to dc charger. No need for a special converter. No worries about going to 0 volts.

The problem I have is that when you ad shipping on the site you linked,the price is right there with the less expensive lifepo4 batteries...Some of the cheapie lithium batteries are not bad at all as shown by Will P...SOC comes to mind.

[ticki2]

This is probably a dumb question , forgive my ignorance . I have been reading about these new technology batteries , lithium and now Sio2 that can be discharged to 80 and 100 percent . How do they power equipment that requires 12v to operate like a furnace sail switch , at this state of DOD ?

[NRALIFR]

I don’t get that “protect the alternator” advice at all. Assuming you were going to connect the Li battery directly to the alternator, wouldn’t you also install a fuse or CB to protect it?

But, the more important point is that if you are going to put the money into a lithium battery, a DC-DC charger will charge that battery better than connecting it to the alternator anyway. The DC charger will be connected to the starting batteries, and will just be another electrical load on the system. In fact, if SiO2’s are the drop in replacements they claim to be, a DC-DC charger (with a solar input in Ralph’s case) would be the best way to recharge them as well.

Even in a TC, the charging circuit to the camper batteries is surprisingly long, and while you can minimize the voltage drop, you can’t eliminate it. Install a DC-DC charger with adequately sized wires and forget about voltage drop entirely.

:):)

[time2roll]

The fuse will open or the wire will melt before the alternator sustains any damage.
Assumes you are using the OEM charge connection.