Battery charging with diferent Voltage

jimskau · October 2008

I have recently purchased an IOTA Engineering 55A/12V charger for my 12V solar system. The charger has proven a great asset in the cloudy autumn weather.
Now one of my neighbors are asking for a helping charge. Problem is his system is 24V (4 x 250 Ah 12V mono bloc batteries, wired in serial/parallel to make 500 Ah 24V).
Question is whether the IOTA 12V charger can be connected in a 12V parallel connection safely along side the 24V 1500Watt inverter (wired in diagonal at extreme opposite 24V +/- terminals)
The Inverter obviously will be shut down during the charge cycle of the IOTA. A 3 Way switch will direct the generator output to the house & charger and disconnect the Inverter output.
My first impression is that we have to make a 12V "jury rig" for the charger circuit, only to be connected during the charging, but if the wiring could be permanent in place it would be a lot easier. Would blocking diodes be useful, in which case what size, where to put & where to get?
Maybe an economic Transformer to step up the 12V output to 24V?
Any suggestions to the wiring would be most welcome.
Jim

niel · October 2008

Re: Battery charging with diferent Voltage

if you were to do this there are too many possibilities of something going wrongly with uneven charging being the least problem. it may be best for your buddy to get a 24v charger than to risk something going wrong trying to use your 12v charger. if you insist on charging his batteries with your charger then disconnect all of the batteries and arrange them to be charged in parallel or individually until they reach their charge with no other charge sources or loads connected to them.

Brock · October 2008

Re: Battery charging with diferent Voltage

I am a bit confused (nothing new) I think you want to try to charge his 24v bank with your 12v charger. But do you mean to rewire his bank to 12v and then charge it or just charge 1/2 of the bank at a time?

Honestly either would technically work, but as Niel said unless you have no loads on the bank from the time you start charging until it's done you will likely mismatch the charge states on the battery bank (not a good thing). In a pinch or done once or twice it's probably not a big deal, but if you do it regularly you will likely damage the bank.

I would suggest having him buy a second matching DLS 55 and attach his to one side and yours to the other. You can charge this way and draw power and it won't hurt the chargers or inverter. Or better yet have him buy an Iota DLS 27v version in the 40, 25 or 15 amp versions and just use that straight, basically a 24v version of what you have. That would be much less expensive then trying to step up the 12v to 24v.

Again the nice thing with going this way is you can fire up a genset power the iota sucking say 1000w from the genset charing the batteries at 1000w. Then the inverter draws whatever it wants from the battery bank. Say your drawing 500w off the inverter, then you’re still charging the battery bank at 500w, but if a load kicks in drawing 1500w, now 1000w is coming from the genset via the iota and 500w from the battery bank and when the load shuts off, your back to power a 500w load and charging the bank at 500w.

mike95490 · October 2008

Re: Battery charging with diferent Voltage

Messy.

Get a 24V charger.

You can jurry rig a way to charge 1 12V battery at a time, but it will only be a short time before you rig a wire wrong, and <BOOM>

How the heck does he charge it currently ? A PV controller ? maybe you can supply 35VDC to his PV input and back feed his PV array at night and charge his batteries.
Still messy.

Battery charging with diferent Voltage

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