Battery Charging Current with Power from on-board Generator

March 18, 2003, 08:53:18 pm

Hi Folks,

I have some data to share with you. This is to answer a question concerning charging current during use of the on-board generator (PowerTech 8Kw diesel and Heart 2Kw Inverter/Charger). This issue was raised at the Las Vegas pre-rally (14-18 March 2003).
Conditions: Shore power disconnected, on batteries, inverter on, operate microwave for 30 sec with cup of water for load, battery voltage was 12.7 vdc after microwave operation; during operation, approx. 140 amp load was observed (using 1% accuracy hall effect toriods for sensing).

Generator turned on, after 2min 15 secs, generator on line and after a few seconds, inverter/charger starts supplying 82 amps to the batteries (saw as high as 140 amps when microwave was run for 1 min periods to discharge batteries). Voltage read approx. 14.5 vdc after microwave operation. After about 13 min, current fell to 12 amps, at which time bulk charge was removed and trickle charge started with a voltage of approx. 13.5 vdc. Conclusion - house batteries get a fast recharge under these conditions. If the batteries (8D)are discharged to 50% (12.25 vdc) or 100% (11.9 vdc), recharging will be longer at higher amperage. Both voltage and amperage readouts are helpful, but accurate voltage readout will provide the best indication of battery health. RULE OF THUMB - try not to let the batteries go below 12 vdc.
Fred Kovol

Re: Battery Charging Current with Power from on-board Generator

Reply #1 – March 19, 2003, 08:23:38 am

Yahoo Message Number: 4425

Fred

Great observation! I also have the Freedom 2000 inverter/charger and PTS 8kw generator. I have noticed similar observations as well.

Bill Darden's web site offers some interesting observations in that the deep discharge cycles is what is so hard on the overall life of the batteries. He discusses that when batteries are discharged to the 50% point then the damaging effects of that discharge cycle begins to become logarithmic. Reducing the average DoD (Depth-of- Discharge) will significantly increase a deep cycle battery life. For example, a battery with an average of 50% DoD will last twice as long or more as an 80% DoD; a 20% DoD battery will last five times longer than a 50% DoD. Golf cart batteries that average 225 cycles at 80% DoD will increase to 750 cycles at 50% DoD. He says, try to avoid DoD that are greater than 80%. This is apparently OK for industrial, traction, and stationary deep cycle batteries with solid lead plates that are designed for average of 80% DoD, but most Marine/RV and golf cart deep cycle batteries with sponge lead plates are designed for average 50% DoD. At an 80% discharge on a RV deep cycle battery, the battery is at 12.00vdc and has already been damaged.
Anything beyond 50% DoD, which is 12.25vdc, the battery likely takes a beating during the recharge process because of high current rates from the charger and generator. Of course the rate of charge can be somewhat controlled in the power sharing features of the power management panels used with the Heart system. I am not sure at what points in the state of the battery charge the battery begins to be hit too hard in the recharge process. I would think it would be directly related to the temperature state of the electrolyte. It would be interesting to build a chart with enough data points to see the change in the charge rates and its effects on the projected life of the batteries.

The most common cause of premature battery failure is lead sulfation. Sulfation begins and continues when the battery is below a fully charged state. Batteries in storage are one of the most affected unless a float charge is maintained.

Bill Darden's web site along with Phrannie's and some of the manufacturer's, offer some excellent discussions on deep cycle batteries.
http://uuhome.de/william.darden/dcfaq.htm>
http://www.phrannie.org/phredex.html>

Jim Hughes

Jacksonville, FL
2000 Allure #30511

Country Coach Owners Forum Country Coach Motorcoach Forum