Battery Charger

I need to quote to install a trickle charger on the battery for a standby genset.

There are two batteries in series, 160Ah each.

Generator only charges these batteries when running, there is no built in charger which is unusual.

What are the better makes of charger?

I am assuming it is not ideal having a trickle charger charging a battery at the same time the running generator is charging it!?! That cant be too good! I assume I should therefore incorporate a relay to isolate the charge circuit when the gen is running.

Opinions guys?

You need to "Float" charge the batteries i.e. hold them at 13.2 volts each years ago I would use CB power supplies to do this it was cheap way out. Also a 7812 voltage regulator chip with a red LED on common will give 13.2 volts common trick for cheap charger but before the engine is cranked it must switch off. Relay on ignition circuit is common. Battery drops to approx 9 volts on cranking.
Any "Trickle" charger is likely to over charge the batteries and they will lose water and require topping up and many can't be topped up.
An "Equalizing" charge every month or so maybe good but not a "Trickle" what type of battery are they lead acid or Ni/iron the latter will not need a float charge.
Also if the generator is run up once a month again it may not need it much depends on maintainance.
Eric

There is a schedule in place to run the gen on load every 3 months, and fire it up off load every month.

However.......It is fairly obvious this is never done.

I said the same thing to the facilities manager - It needs running as per the schedule, and this will keep the batteries in a good condition.

As the two batts are inseries, a 13.8v PSU would not be suitable anyway.

I shall look into it....

I work with a set of emergency lights (distributed) which have a trickle charge facility - not much more than a transformer, a rectifier, an ammeter and a couple of bayonet lampholders connected in parallel with each other.
Assuming the batteries are fully charged it is just a case of trial and error with different wattage lamps to get about 20mA to flow to keep the batts topped up.
(Is a 1950s chloride unit btw!)

Although you can but or build a 24 volt unit (26.4 volt) there is nothing to stop you using a pair of 24 volt units if you can get a center tap.
Be careful in selecting battery chargers as the ones designed for fork lifts gives a rapid charge until a voltage threshold is reached then a lower charge for set time then switch off so the battery would still go flat over time.
You may wish to consider a blocking diode depending on 24 volt alternator fitted to generator. Unlikely to be required. I have built chargers into main control panel before now.
Many generators use the generated/standby power to do all the charging and have an idler in place of the 24v alternator normally fitted.
Eric

From my limited experience, I can recommend that you don't buy anything made by Benning. We have one of their chargers at work, it's a modular rack mount unit and it's probably a touch over five years old. It has hot-swap rectifier modules, and they seem to be forever failing and being sent for repair.

On the other hand, we have four or five other chargers of similar output (~150A @ 28v) that are subjected to the same level of use and abuse, they're at least 15 years old and I've never been called to a fault on any of them. Can't recall who they were manufactured by, they might have even been a custom build. All the charger needs to do is output a set, regulated voltage and the rest will take care of itself. However, this is not the right kind of charger if the batteries may ever become depleted, as the charge current can easily run away when the difference between charger and battery terminal voltage is high. Of course, this should never occur in a pure float charge application!

I assume the genset uses lead acid batteries? If that's the case, I'm not 100% sure the concept of 'trickle charging' exists, you'd probably be referring to a float charger. This is where the charger holds a constant output voltage a little above that of the cells, and a very small amount of current equal to the cells internal self-discharge rate is provided in order to keep the batteries charged. This is pretty much self regulating, in that once the battery is at nearly full capacity, the charge current will diminish until only just enough is being drawn to keep the cell topped off.

If you may want to charge the battery from flat then you should consider a three-stage charger. These usually start with a constant current (bulk) charge of, say, C/5 Amps, up until the voltage at the terminals reaches a set point. After this it'll switch to a constant voltage (equalisation) charge and wait for the charge current to reduce to a set limit indicating that the cell is nearing full capacity, and then finally move onto a lower voltage to provide continuous float charge.

As you say, it would be wise to have the charger's output disconnected when the set is running.

I think I would contact an FG Wilson agent. I know they supply replacement chargers for their sets which I'm sure you could adapt.

I did quick internet search and http://www.powersuppliesonline.co.u...e-stage-sla-battery-charger/l04ab/default.htm seems to fit the bill and at £30 not sure it warrants too much of a hunt for better unit.
Eric

ericmark said:

I did quick internet search and http://www.powersuppliesonline.co.u...e-stage-sla-battery-charger/l04ab/default.htm seems to fit the bill and at £30 not sure it warrants too much of a hunt for better unit.
Eric

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That looks a good charger, but I would put it on a timer so that it is only on for, say, 2 hours a week.
I used to have a similar unit float charging my generator battery, but I found it killed the battery after a year or so. I have been using a timer for 5 years with no problems.

I've got a similar one for a kiddie car I built.
The batteries are much smaller (4 x 18Ah) but it's fine, so I would say there is little chance of it damaging larger ones.

Good point about a timer though, they are cheap and it can't hurt can it? A couple of hours a day should be more than enough to recover any lost charge

No do not use a timer as it has double function and each time the power goes off it will over charge the battery with once a month is OK as it is considered as equalising charge but Chris.J the model I located would over charge if repeatedly switched off.
With a cheap trickle charger a timer may work.
Other option I used with caravans is a add on overvoltage sink I used a power opamp to a 2N3055 transistor and 36 watt bulb and a potential divider and 7805 regulator as voltage reference. As the voltage raised above 13.2 volts the transistor would start to conduct and power the lamp and the lamp would slowly glow more and more showing state of charge and stopping over charging but since it also has built in alternator I did not think this was appropriate in this case.
The charger I selected is not best for job as it only requires the float function but I couldn’t find one at reasonable price.
I use my variable power supply 0 – 30 volt and 0 – 1 amp but the cost is a little silly and not really warranted and as long as the one I pointed out is not switched off it would do the job OK.
Eric

Chris.J said:

That looks a good charger, but I would put it on a timer so that it is only on for, say, 2 hours a week.
I used to have a similar unit float charging my generator battery, but I found it killed the battery after a year or so. I have been using a timer for 5 years with no problems.

Click to expand...

Obviously I can't argue with your results, but it was more likely down to a problem with a poorly designed charger or cheap battery rather than the method of charge.

Still working on the assumption that the genset uses lead acids (can't see it confirmed anywhere by OP?) then you should have no problems with a continuous float charge. As Eric points out, a timer with a multi-stage charger will do more harm than good as it'll continuously repeat the charge process each time it gets powered up. The charger should detect pretty quickly that the battery is full and switch to float charge, but it's still an unnecessary strain on the battery.

If you want proof that float charging is safe then take a look at an alarm control panel. Most contain some sort of lead acid cell that is continuously charged, and as long as a quality battery is fitted and the ambient temperature is kept within sensible limits then it will last for years.