I have read quite a few posts on various fora regarding the best DC-DC charger.
Whether something is a good solution depends on your circumstances and how you intend to use it.
Here are my thoughts so far in an attempt to pull together some Pros/Cons for general consumption and info on some of the available products.
If the thread doesn't go too far off track or degenerate I will pull in into a spreadsheet later.
I think sometimes it is assumed that everyone has a Landcruiser or similar with stacks of engine power.
We previously had a 1996 Forester and just got the diesel Santa Fe.
With a smaller engine car you actually notice the additional load on the alternator - especially towing up a
hill...
The other thing I have noticed is that the new Santa Fe ECU actually lowers alternator voltage when accelerating and increases alternator voltage when stopping - I read in the US service manual that it does this for marginal gains in fuel efficiency. Measured at the cig lighter I get as low as 13V.
Weight is another issue that is sometimes neglected in pros/cons.
For a camper trailer mounting location is an issue also. Put it in the toolbox and it will get hotter due to poor ventilation. Put it under the side of the trailer and it be ventilated but exposed to dust and water...
With this in mind, some of the benefits of a DC-DC charger MAY be:
1. Limits alternator draw.
2. Limits
battery current (for smaller
battery systems or parallel charging).
3. Prevents back-feed of current from aux
battery back to ECU managed
battery (ie doesn't interfere with ECU).
4. Allows a car with ECU managed alternator voltage to get to absorption charge voltage and to maintain that voltage.
5. Compensate for additional voltage drop in the cabling into the DC-DC charger (however you should try to minimise losses in cabling as far as practiucal anyway).
6. Reasonably simple installation.
Issues with DC-DC chargers MAY be:
1. When connected in parallel to other charging (eg solar) there is no co-ordination between chargers - if you can set charge voltages slightly lower than the solar charger this may be overcome to some extent.
2. As discussed already the DC-DC charger does not know
battery current and therefore either goes off time or output current or adapative algorithm (usually time in bulk charge and/or discharge volts?).
3. Possibly more expensive and prone to failure than something unsophisticated like a solenoid relay?
I have a camper trailer and planning a setup with 2 x 135W panels on top of the Santa Fe, 2 x 75Ah AGM in the camper and want a method of "boosting" the charging from the panels if necessary.
Here are the DC-DC chargers I have considered and some comments on each (alphabet order - IP is protection from dust/fingers and water - wiki it! "no IP" below just means not suitable for unprotected).
I haven't included efficiency as it is variable over input and output conditions and not measured to a comparable standard (ie virtually useless IMO).
Also haven't gone into the gory details of input/output protection, isolation etc.
Warranty would also be a good addition.
Please feel free to comment on accuracy or add anything extra.
ABR Sidewinder SDC-1120 (~$???, 1.4kg, 20A, no IP, 30mA off, no temp comp, batt type sel, temp ctrl fan)
Can operate as a constant voltage power supply (13.2/13.5/13.8). Couldn't find out if this is still available.
ABR Sidewinder SDC-1130 (~$250, 1.9kg, 30A, no IP, 30mA off, no temp comp, batt type sel, temp ctrl fan)
Can operate as a constant voltage power supply (13.2/13.5/13.8).
Arrid TwinCharge BCTC20 (~$, 0.6kg, 20A, no IP?, ?mA off, no temp comp, no batt sel?, fan)
Can't seem to find an online manual or detailed specs for this unit. Lots of people have them though so it is strange.
CTEK D250S Dual (~$400, 0.7kg, 20/16A, IP65, 4mA off, temp comp, no batt type sel, fanless)
Takes DC and MPPT solar panel input and can use both at same time but not in MPPT mode. Can output 20A but CTEK Sweden have indicated it will derate to ~16A @ 40degC ambient. Can parallel 2 units for double the output. Adaptive absorp charge time. Can use a 12VDC power supply as the input as a cheap mains charger (ideally ~16VDC power supply for max efficiency). Can also add a SmartPass unit to increase initial bulk charge current (up to 80A).
GSL MCB12-25 (~$???, 1.4kg, 25A, no IP, ?mA off, no temp comp, batt sel, fan)
Not much info available.
Philippi LMB 12 (~$???, 2kg, 100A, IP21, ?mA off, temp comp, batt sel, temp ctrl fan)
Not sure if you can buy this yet. Has optional remote display. I think you can select maximum amps also. Has remote sense for alternator and
battery voltage and for alternator temp.
Projecta DC20 (~$???, 2.2kg, 15/20A, IP55?, 10mA off, no temp comp, no batt type sel, fanless)
End of absorp at charge current <3A.
Ranox - not available anymore?
Redarc BCDC1220 (~$450, 0.45kg, 20A, IP55?, 5mA off, no temp comp, batt type sel, fanless)
Output derates at higher ambient but with adequate ventilation it should be full output at 40degC. Not sure how absorp charge is ended.
Redarc BMS1215 (~$1550, 2.4kg, 15A, no IP, ?mA off, temp comp, batt type sel, fanless)
Not just a DC-DC charger. Also does AC and solar MPPT charging. Controls end of absorp charge on
battery current not time. Also has a display that you can hook up on the camper or in your towing vehicle with
battery SoC and history. Unfortunately limited to 15A output (couldn't confirm if it did this in 40degC ambient). Too small for me, but could suit a Gas fridge setup nicely. Only allows charge from one input at a time.
Sterling Power BBW1220 (215Euro, 2/3kg?, 20A, IP68, ?mA off, temp comp, batt type sel, fanless?)
Couldn't get much info on this one. Sterling
temperature specs seem very good.
Sterling Power BB1250 (342Euro, 2/3kg?, 50A, no IP, 3mA? off, temp comp, batt type sel, temp ctrl fans)
Adaptive end of absorp charge based on time to reach absorp voltage. Remote display option. Sterling
temperature specs seem very good.
Regards,
Mike