Lead acid battery chargers, for a generator diesel engine. (Again) - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: January 16, 2024, 12:29:18 pm
content: Thanks to some great help from these forums I made a constant current battery charger for my own diesel generator engine starting battery.I have been asked to do something similar for a friend's gennie, but ather than the labour intensive rather unproffesional looking home brew route I was thinking of using one of these battery monitor / protector / charger shut down gizmos off Ebay:https://www.ebay.co.uk/itm/314100477394?var=612759040441Tested with a bench power supply and a small gel type 12 volt battery it seems to work well.My question is regarding what permanent mains power supply to use? The generator has a pretty damned big battery, but should only need maintaining at a voltage well able to start the thing reliably as it depletes from the small load from the mains monitoring auto start controller.I have some very nice industrial 12 volt, 6 amp switch mode PSU's. They have a voltage adjuster pot inside, but the most they'll manage is 12.8 / 12.9 volts out.Would that be enough to maintain the battery? The gizmos merely switch either mains to the charger / power supply, turning it and its output on and off according to max and mininimum battery volatage sensed.Or they switch the permanently on charger's / PSU output on and off, with a relay. So there's no voltage drop unless I put a Schotkky diode in the battery feed to be sure no back feeding can occur (I don't *THINK* one is neeeded, but....).I also have a broken (probably a blown pass transistor) 13.8 volt, 10 Amp regulated linear commercial power supply that could probably be fixed.How much unregulated output volatage and current is the minimum I need from a transformer / rectifier to keep the battery topped up in a healthy state please?Thoughts, criticism, (even laughter) welcome!Thanks.

author: CaptDon
author_rank: Super Contributor
timestamp: January 16, 2024, 05:28:33 pm
content: 12.8 / 12.9 is to low for a lead acid battery. It will probably begin to sulphate badly within one year. Something around 13.6 would be a better number. 13.8 and above could promote excess out gassing and loss of fluids. A few things come to mind. Running the generator weekly or at least once per month until completely warmed up (30 minutes) to keep condensate out of the oil. Being diesel, winterizing the fuel if the fuel is at outdoor temperatures and also a block heater if the generator is in the outdoors. If possible, no load on the generator until it has run for at least one minute to stabilize and lubricate rod and main bearings and reduce 'hot pistons in cold cylinders' which is worse when cold loaded. Steel or iron cylinders shrink when cold and if the pistons heat rapidly from high throttle positions during cold start up you get excessive wear. Some 'instant start / full load' units have extra piston clearance and they rattle like a skeleton until everything gets to normal operating temperature. Some of the full load cold start units actually sound like the innards are going to come flying out for the first few minutes!! (My experience EMD 710 V20 stationary prime movers in generator service. Most experience is in railroad locomotives where V20's were quickly taken out of service and replaced with V16 or later V12's). A brutal way to observe reserve cranking capacity is to kill the fuel supply during the first 10 or 15 seconds of cranking to extend the crank cycle and observe battery voltage drop!!! I have seen cell caps blow off of sulphated cells doing this (along with the sulphur stink).