The Offshore Voyaging Reference Site

Smart Chargers Are Not That Smart

JHH5-12215

Charging batteries properly is complicated by the fact that most battery chargers are, despite the claims made for them, not capable of charging any battery properly. Or at least not without a lot of user intervention.


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More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—Part 1, BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Part 2, Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Part 3, Current (Amps) Requirements and Optimal Voltage
  33. 11 Steps To Better Lead Acid Battery Life
  34. How Hard Can We Charge Our Lead-Acid Batteries?
  35. How Lead Acid Batteries Get Wrecked and What To Do About It
  36. Equalizing Batteries, The Reality
  37. Renewable Power
  38. Wind Generators
  39. Solar Power
  40. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  41. Battery Monitors, Part 1—Which Type Is Right For You?
  42. Battery Monitors, Part 2—Recommended Unit
  43. Battery Monitors, Part 3—Calibration and Use
  44. Battery Containment—Part 1
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Bob Tetrault

I’ve continued my practice of lead/lagging my two house banks even though plugged into the boatyard. I have the same chargers as you and recently completed conditioning of all four banks that have these dedicated chargers. I experienced some of the same frustrating revelations as you. I can isolate my loads and condition banks while the batteries are at rest so it wasn’t quite as challenging as you write. Justin instructs us to condition at 15.5 volts (room temp) for eight hours. The chargers as you know cycle off at six hours so one must set the alarm and re-introduce the cycle for two more hours. Also my chargers must be programmed at 15.7 volts because three of the four held that voltage for the cycle even though the battery temperatures varied ten degrees (F) or so. My battery temperature didn’t rise appreciably so the pre-programmed conditioning voltage was a non issue. One charger refused to enter conditioning mode even when fooled (flooded batt pos), actually it adopted the mode but refused to come above 13.7VDC. I replaced the charger with the spare and all is well again. I agree with your idea that this is an expensive process when away from the dock. I can expect the generator to run 16 hrs or more for this monthly exercise for each house bank. I do not count amps as you know but rather rely on voltage to determine battery condition. I think the amp counting is too complicated and subject to error and it’s one more thing for this old man to manage.
I look forward to your research on alternator charging as this may be my Achilles heel here on Sea Return. We do not use a three step regulator and charge every battery through a Mastervolt battery isolator, hitting all with as much as 14.2 vdc. For the house bank we keep the switch on all while alternator charging because we charge through the switch for the combined house bank. Not all the banks are under load so we may be heating some more than we should but everything stays topped up while underway. With the new engine install we plan to place two 90A alternators on the engine feeding that same Mastervolt battery combiner simultaneously. This deviates from my long time practice of avoiding belt drives but David (ace machinist at Billings) will engineer the two dual belt drives which should be a durable work of art. I also believe in not combining components in a single case so that will begin to explain the two sine wave, one square wave, inverters and four Statpower and one Newmar charger. Good luck with your continued research, we should all benefit in the end.

Eric Schlesinger Sue Peterson

I guess I may have missed something in your battery discussion. I have two smaller Rolls. I use an inexpensive Sears 110 charger. It tells me what the outgoing current is. Couldn’t you isolate one battery at a time to charge and use the others to run the ship until that one was fully charged then switch to the next…?

David Beresford

We are getting ready to go to the Arctic with a 24v only boat and would suggest keeping batteries warm with a diesel heating system. How say?

Rick Clark

GPL-L16T Marine Battery, I plan on using 2 of these 6volt bats on my 38 year old 20′ Ensenada. I was wanting to know what is the best way to charge these bats as a 12 v system or isolate and charge as 6 v.
These are 400 amp/hr bats each. Will the system be 800 amp when seried to have my 12 volts? Also, I only have room for one solar panel, I’m thinking 235 watts. What kind of charge controller will have a 3 step charge control for AGM batteries?

Kees Verruijt

I’ve installed a new Mastervolt based system on our new boat. This has the advantage that it ties all chargers, inverters, shunts, etc., together with (optional) remote control panel(s). The trick here is that you can tell the charger to interface with the shunt so that it knows how much charge actually goes into the battery.