Thanks everyone for all the replies - much appreciated
Terry - I got the impression when I was googling a lot of the manufacturers seem to throw a mention re lithium as an after thought
Firegirl - I did see your post re using the eBay cheapie, I assume it's still working. I can't remember whom but another Forum Member purchased one/two and was going to do some tests with it. I am a bit loathe to connect alternator charging directly with the current hungry nature of lithiums so was investigating the dc-dc option with the view of having it limit the charge current.
Hi Eddy, Just a suggestion...why bother at this stage?
The setup seems to be working fine in the garage with panels on roof - just wanted a backup for a planned Gibb road trip
Eddy if you have an MPPT charger, especially a Victron Blue, I have one of of the cheap eBay 15A DC-DC which you can try. It's the one Firegirl is using, but didn't work in my application with PWM.
Just goes to show eh, we asked the local Jaycar store to do a country wide search and they came up with nothing available and a revised part number to MB3689, you will find the same thing happens if you click on the link Lance put up. Maybe Jaycar simply dumped the part number so unless the store staff do a hands on search they won't know they have them.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
Thanks Steve
I am using the Electrodacus unit I will be connecting the dc-dc unit straight to the battery and the Electrodacus will monitor charging and the remotely turn off charger when all charged (I hope)
Leslie 's (Firegirl ) unit talks about 19v at 20 amps I think with the voltage probably not suitable for what I need - I guess the Victron adjusts the 19v down to a more suitable level
Eddy wrote: ↑Tue Feb 27, 2018 1:48 pm
Thanks Steve
I am using the Electrodacus unit I will be connecting the dc-dc unit straight to the battery and the Electrodacus will monitor charging and the remotely turn off charger when all charged (I hope)
Leslie 's (Firegirl ) unit talks about 19v at 20 amps I think with the voltage probably not suitable for what I need - I guess the Victron adjusts the 19v down to a more suitable level
Thanks for offer Steve
Yes, needs to be coupled with an MPPT controller that will maintain the 20v or so in and adjust the output voltage to suit the battery condition. A cheap option if you already have the MPPT controller, not a cheap option if you need to buy one of those as well. Roughly $250 for the Projecta IDC25 on evilbay, so not a bad option. No idea regarding the capabilities of the Electrodacus unit as far as aux charge control goes, probably has a programmable relay output that could be linked to a solid state relay to cut the feed in from the start battery if a cell goes high voltage. I have no idea what effect feeding the Dc to DC output into the solar input would have in regards to either the Projecta unit or the Electrodacus unit. I'm guessing the Electrodacus unit wouldn't have an issue but the Projecta would see solar open circuit voltage once the battery reached fully charged and I don't think it would be really happy about that. Maybe a diode capable of handling the 25 amps on the output of the Projecta unit so it never sees the solar open circuit voltage and only the Projecta output voltage .... depends if the Projecta unit requires battery voltage to be sensed before it turns on.
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
Terry - you pre empted my light bulb moment, sitting in the shed staring at the lithiums as you do, I thought why can't I hook the Leslie unit in the solar input side, the solar panels have blocking diodes fitted, I need to read specs of Electrodacus unit again
The Projecta web site shows the 25amp lithium dc-dc charger as still a work in progress is this the one you are referring to or modifying the charge characteristics of the IDC25 which is on eBay for around $250
Eddy wrote: ↑Tue Feb 27, 2018 3:32 pm
Terry - you pre empted my light bulb moment, sitting in the shed staring at the lithiums as you do, I thought why can't I hook the Leslie unit in the solar input side, the solar panels have blocking diodes fitted, I need to read specs of Electrodacus unit again
The Projecta web site shows the 25amp lithium dc-dc charger as still a work in progress is this the one you are referring to or modifying the charge characteristics of the IDC25 which is on eBay for around $250
Thanks
The unit that is on Evilbay for $250 will do the job fine, the "lithium" unit I expect will just be another case of a battery voltage sensing charging routine with no cell voltage sensing or input from a BMS unit designed to control the charging input.
As far as the DC to DC unit that puts out 19v plus, it needs to be held up at that voltage to work as designed and the direct connection to the battery that any PWM unit will make will pull the output voltage down to battery voltage resulting in the cheapie DC to DC either letting the smoke out or simply not working the way you had hoped.
T1 Terry
T1 Terry
A person may fail many times, they only become a failure when they blame someone else John Burrows
Those who struggle to become a leader, rarely know a clear direction forward for anyone but themselves
Hi Eddy,
Be careful hooking one of the cheapie dc dc things to the solar input side of anything but an mppt unit that is specifically designed to limit current when xs solar input is connected. The victron one we have does this (we already had it so the dc dc thingo was a cheap add-on). If you hook it onto something that can't handle it, it may just fry itself and possibly whatever you connect it to.
But when used with the victron it works unbelievably well (so far anyway, only used it a couple of times for a couple of hours each time). I thought it would get hot and so mounted it on a bloody great heat sink.....but it stays cold and measured efficiency in our application has always been over 97%!!!!
Cheers, Leslie
