Using old and new battery together, thoughts please.

[ericmark]

Above battery A you can see the multi-connector to right which connects to the scooter, not sure why so many, as it is simply duplicate 24 volt DC connection. In centre you can see where it connects to battery B.

Battery B has a simple two pin connection which simply connects to battery.

So to get a 12 volt connection to battery A would require one connection to side connector and one to rear connector, so at the moment battery case open so a smart charger is simply clipped onto the battery, because it is a smart charger designed to charge 6 or 12 volt batteries as a 4 stage charger, it will not as it is charge the battery as the voltage is below 7.5 volt required to switch the charger into 12 volt mode. So there is a 7 Ah battery in parallel to trick the charger into working, once removed the voltage goes over 15 and this turns the charger off.

This is not the first time I have done this, and in the past it has after a week or two as if some one has flicked a switch started to charge, the battery has been left discharged for a year, however when the other battery failed it may have damaged this battery, so it may never recover, but no harm in giving it a go, if one cell is shorted the charger will only supply 0.8 amp and the 7 Ah battery will not transfer a dangerous amount of energy so quite safe. At the moment holding at 13 volt with no output out of the charger, if it drops to 12.7 volt then charger will switch to 0.8 amp output then 0.1 amp, so will be a slow charge, but as you say that is good.

So since a simple 6 mm bolt to connect battery, easy enough to at cables with a ring terminal, but trying to work out an easy way to get a connector to easy connect to 12 volt charger, in a way where loading into a car can't result in a short circuit.

 

[bernardgreen]

In terms of charging off the scooter, you can connect them in parallel and charge at 12V - double the current.

Connecting two batteries in parallel requires some protection circuitry to prevent one battery ( with 6 good cells ) discharging through the other battery when that other battery has a dead cell and is in effect a 10 volt battery.

Best case is the good battery does not get charged as all the charge current is going into the 10 volt battery

Worst case is the dead cell over heats.

 

[SimonH2]

I was assuming a new pair of batteries.

The connectors are powerpole, so easy to make up matching (mating) sets. They've doubled up to improve current rating - but not done that for the connection to the second battery !
Just to confirm, on that big one between battery & buggy, there's definitely no connection to both sides of that battery ? It looks, as best I can see from the photo, as though there are separate connections for the two batteries. It looks like a pair of red and a pair of black disappear round the back and connect to that battery - with separate red & blacks for the second battery connector.

As already mentioned, it would be preferable to charge as a set - either as 24V or in parallel as 12V. Otherwise there will be a temptation to use the buggy when one of the batteries isn't fully charged - and then you run a much greater chance of damaging the cart charged one through over discharging.

If I'm right about the connections, you could make a matching connector for the big multipole which would parallel the batteries to charge off 12V.

 

[bernardgreen]

I was assuming a new pair of batteries.

With batteries never assume......sulphuric acid close to boiling point is not a nice liquid........

 

[ericmark]

Yes the two batteries are as 24 volt only, no connect to bridge between batteries.
So the two multi connection plugs only connect to each other, two blacks and two reds go from one plug to other, they must tell the scooter a battery is connected. The larger of the two multi plugs also has two 24 volt pos and two 24 volt neg that takes power in/out of scooter. The smaller plug and socket just two connections brings the second battery into the master to make 24 volt, there is also a 120 amp fuse and a 40 amp over load connected between the two batteries.

The charger has three pin plug, it would seem only 2 wires connected third pin to make polarity correct only.

There is a 7.5 amp fuse between charger and batteries, and stage charger rated at 5 amp. So from flat at least 7 hours to charge.

I have two identical Lidi 6/12 volt smart charges 3.8 amp, since likely will have one new and one old battery charging independent seems a good idea, may be able to get plug for battery B but battery A would be a problem, so seems better to fit some thing to allow charging off scooter, ideal would be cig sockets, but don't think enough room. Ideas welcome, would be nice if I could use batteries for caravan things, they are in a good case designed for carrying in the car so a handy power pack.

Connecting two batteries in parallel requires some protection circuitry to prevent one battery ( with 6 good cells ) discharging through the other battery when that other battery has a dead cell and is in effect a 10 volt battery.

Best case is the good battery does not get charged as all the charge current is going into the 10 volt battery

Worst case is the dead cell over heats.

I had considered that which is why the other battery is so small, 7 Ah is not going to push much power into the battery, and I can monitor from phone, tablet and PC so will soon know if it starts taking a charge.

I have now found a manual here which has the battery wiring diagram

Just need to sort out some plug and socket arrangement.

 

[bernardgreen]

I suspect the batteries are connected by plug and socket to make a single 24 volt ( 12 cell ) battery

The fuse in Box B is there to protect against any shorts that might occur in the connections in red.

 

[ericmark]

Yes correct, but the plugs and sockets are held in place by the wells in the scooter, and a pin. So once removed the interconnection between the two batteries is not really good enough, trying to connect them together could damage the plug and socket, ordering a plug and socket on internet I have in the past ended up with some thing unsuitable, too big, too small, easy damaged, etc. Might end up with

and an in-line fuse. Would prefer socket for these

but they seem too big.

 

[SimonH2]

Go check out the powerpole connectors. Slot 8 housings together and you have a polarised connector that will mate correctly with the big connector - and it will stay mated on it's own.
They housings are only to align the connectors as people heavy handedly drop the batteries in place. The connectors are quite robust. PM me an address and I'll post you some to play with - I've kept them when scrapping old UPS batteries.

 

[ericmark]

Odd I would have expected the charger to switch on every so often to maintain the voltage, I manually switched it off a few days ago, and it ran at 0.1 amp for around 6 hours until 14.4 volt when it switched off and the voltage slowly fell to 13 volt, it needs to fall to below 12.8 volt to reinitialise charging, so since when done manually it charged for 6 hours, I know I would not miss it starting to charge, even if the scooter battery was no in parallel I would not have expected a VRLA to hold the voltage for so long.

I thought I knew lead acid batteries, but now find I am still learning.

 

[ajohn]

I worked on the things for a few years. I don't think charging them in parallel is that good an idea but should work and in some ways better than charging them is series providing both are new. Hard to say what will happen with one new and one old. Best option really is 2 chargers. 12v batteries have 6 cells in series and often some fail before others. 2 batteries in series makes that aspect worse.

If you don't replace both the new one will just hold the volts up longer leading to lower discharge levels of the old one. If a cell is too low it gets charged in the wrong direction during the discharge, terminal, never be the same again. Might do to try it out on the hill. Leaving them lying around for ages without maintaining charge doesn't do them any good either.

Long term the best option is probably to charge each battery separately from time to time to equalise them - when you fit 2 new ones.

 

[ericmark]

Thank you @ajohn that is what I have been thinking, the range of the scooter is around 20 miles, at 4 MPH that 5 hours use approx, it is highly unlikely it will ever be used for that long, so reverse charge very unlikely, however charged in series the good battery will likely get over charged, I would not charge in parallel once rebuilt, simpler and quicker to use two chargers since I have two both 3.8 amp where the 24 volt charger is 5 amp, however I have noted the charge rates, and very quickly my smart chargers start to reduce the charge rate, so really does not matter if rated 2 or 20 amp, the charge time is nearly the same, it is what the batteries will accept rather than what the chargers can give.

I think some way some how I need to make it so I can charge off the scooter, and think two independent chargers are better than trying to pair the batteries to charge at 24 volt, years ago I would have walked around tandy or maplin and selected some thing to do the job, but neither store exists, so trying to select an appropriate method, if possible so I can still use the chargers for other batteries.

 

[securespark]

I thought I knew lead acid batteries, but now find I am still learning.

Every day's a school day! You never stop learning.