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--- electrical:12v:b2b [2020/03/23 12:52]
frater_secessus [Renogy]
+++ electrical:12v:b2b [2020/06/23 12:20]
frater_secessus
@@ Line 18: / Line 18: @@
-===== CTEK D250 series =====
+===== sizing =====
+DC-DC chargers come in different ratings (10A, 40A, 60A, etc) which increase significantly in price as the rating increases.
+Different battery types accept current at different rates.  Assuming a 100Ah battery:
+* Flooded lead-acid accepts a maximum of about [[electrical:12v:battery_capacity|C]]/5, or 20A and requires a minimum of C/10 (10A).  In this case, **10-20A of charging capacity would be appropriate**.  Less than 10A would be insufficient and more than 20A would be wasted expense.
+* AGM lead-acid accepts a max of about C/3, or 33A per 100A of battery capacity, and requires a minimum of C/5 (20A).  In this case, **20-33A of charging capacity would be appropriate**.  Less than 20A would be insufficient and more than 33A would be wasted expense.
+* Lithium has very low internal resistance, and may be able to slurp up all the alternator has to give.  However, there are reasons not to max out charging capacity:
+  * added expense
+  * lithium does not care about [[electrical:12v:psoc|partial states of charge]]
+  * lithium tends to last longest with gentler charging/discharging
+  * the alternator will be happier with lighter loading
+For these reasons, an appropriate charging capacity would be **as small as possible while still meeting your power needs**.
+===== common examples =====
+==== CTEK D250 series ====
 The most common b2b charger with 'dwellers is the [[https://amzn.to/2RY2GNQ|CTEK D250SA]], a 20A solar/alt controller.  It has connections for both alternator and solar panel input + MPPT function, although the MPPT algo may not be partcularly robust.
@@ Line 26: / Line 53: @@
 Note:  the CTEK D250SA((and the pre-2018 D250**S** model)) panel voltage (Vpanel) maximum is 23v.((https://www.ctek.com/storage/ma/b21ecd5d5e5943a995474cf36d586451/956c3913c8cc4319bb4e47baea0c6d82/pdf/A78BBB08A9DF8976DB79E21271E091489ACEF47A/D250SA-manual-UK-EN.pdf, pdf))  There are user reports that the unit is [[https://www.4x4community.co.za/forum/showthread.php/322874-CTEK-D250S-Problem?s=a2bc518379e50466c9ec523e8b114053&p=4270868#post4270868|repairable after overvoltage or polarity damage]].  It requires >= 80w of solar for reliable solar charging.(())(())  [[https://duckduckgo.com/?q=ctek+mppt+problems&ia=web|There are anecdotes that the MPPT algorithm is not particularly robust]] and is better thought of as an add-on for the alternator charging circuit.((https://expeditionportal.com/forum/threads/ctek-250s-poor-solar-performance.198052/))
-===== Sterling =====
+==== Sterling ====
 [[https://amzn.to/2SkqVXq|{{https://images-na.ssl-images-amazon.com/images/I/41iC+8sIvJL._AC_US218_.jpg }}]]
 The Sterling Pro Batt Ultra series is alternator-charging only, but can be configured to exact [[electrical:solar:charge_controller_setpoints|setpoints]]. The BB1260-12 is a 30A example and costs about $50 more than the D250S above.
-===== Renogy =====
+==== Renogy ====
 relays
 [[https://amzn.to/33HJ8ns|{{ https://images-na.ssl-images-amazon.com/images/I/51Hu4-7NxOL._AC_UL160_SR160,160_.jpg}}]]
@@ Line 37: / Line 64: @@
   * DC1212 series DC-DC isolators in 20-40((and possibly 60A according to manual nomenclature)) output.  Switched on by ignition circuit on the D+ port.((https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf)) DIP switches for battery type. [[https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf|manual]] (pdf)
   * DCC-series of voltage sensing b2b chargers in [[https://amzn.to/2NGIP6U|20A]] and [[https://amzn.to/33HJ8ns|40A versions]].
-  * DCC50S [[https://amzn.to/2QYuswm|50A model with MPPT charging]] - [[https://www.renogy.com/content/RBC50D1S-G1/RBC50D1S-G1-Manual.pdf|manual]] (pdf)
+  * DCC50S [[https://amzn.to/2QYuswm|50A model with MPPT charging]]. MPPT input limited to 25v.((per the manual)) - [[https://www.renogy.com/content/RBC50D1S-G1/RBC50D1S-G1-Manual.pdf|manual]] (pdf)
-===== Redarc =====
+==== Redarc ====
 [[https://amzn.to/2VgTre7|{{ https://images-na.ssl-images-amazon.com/images/I/417F858GCdL._AC_US218_.jpg}}]]
 Redarc makes [[https://amzn.to/2VgTre7|a 25A b2b charge with MPPT]] similar to the CTEK.
-===== Ring Automotive =====
+==== Ring Automotive ====
 Ring makes [[https://www.ringautomotive.com/en/product/RSCDC30|a 30A DC-DC charger]].

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