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--- electrical:12v:diysmartpass [2023/06/23 15:14]
frater_secessus [20A combo DC-DC + isolator: $172]
+++ electrical:12v:diysmartpass [2025/01/26 19:03] (current)
frater_secessus [the problem the Ctek solution addresses]
@@ Line 3: / Line 3: @@
 ====== DIY Ctek D250 + Smartpass setup ======
-This article is about the Ctek combo and possible approaches to duplicating the major functionality for less money and/or better specs.
+This article is about the 1st-gen Ctek combo and possible approaches to duplicating the major functionality for less money and/or better specs.
 This article assumes you want and the bank will accept >20A of alternator charging, and that your alternator can handle it.    If you only have a 80Ah AGM then the combo setup is massive overkill.  The bare D250 would handle that with ease.
@@ Line 20: / Line 20: @@
 [[electrical:12v:b2b|DC-DC chargers]] can boost alternator voltage to the required Absorption voltage but doing so with Big Current can be impossible or at least very expensive.  So DC-DC chargers are usually relatively small.
-Digression: this means that for **short drives** the isolator will likely return more Ah to the battery ban k than DC-DC.  On **longer drives** the DC-DC will both return more current and charge at a more appropriate voltage for the battery chemistry.
+Digression: this means that for **short drives** the isolator will likely return more Ah to the battery bank than DC-DC.  On **longer drives** the DC-DC will both return more current and charge at a more appropriate voltage for the battery chemistry.
 What if we paralleled an isolator with a small DC-DC to get the both of best worlds?  That is what the Ctek combo does.
@@ Line 40: / Line 40: @@
   - stop the isolator from passing voltages >Vfloat from alternator to house bank during Float stage.  This should be a minimal problem with lead batteries((which can usually [[electrical:12v:eternal_absorption|tolerate high floats]])) and with driving times limited to a few hours.    It //could// be a problem with Li batteries and many hours of driving.  Note:  it is not clear that the Ctek combo addresses this issue. The only approaches known to prevent excessive voltage during float are the combo DC-DC and the solenoid + HVD in conservative mode (see below).
   - **isolators have no control over current**.  In reality the combo might make **20A+120A** (dead house bank, big alternator, cool temps, Bulk stage) or it might make **20A+1A** (when battery bank is approaching alternator voltage). There is no guarantee that the DC-DC will be making 20A, either.  If your bank is only accepting 15A then having 140A theoretical on tap will not matter.
+  - provide for [[electrical:12v:self-jumpstarting|self-jumpstarting]].  The method Ctek uses for this appears to be FET-based like main isolation:  "Is a smart combination of relays (actually MOSFETS) that connects starter and service batteries. This enables current from your alternator to charge both batteries".((https://www.ctek.com/storage/5CDB4E293A03CBF6442A620EC8E49CFB548CB48E9BF93425638077279A13BBA1/ac5639c5feaa46d38411ebd69f915b5b/pdf/media/65589cee7d4342e0891e2130149be66f/SmartPass%20120S.pdf))  [Dual MOSFET packs in series? - secesssus]
@@ Line 61: / Line 62: @@
-==== 20A combo DC-DC + diode isolator: $173 ====
+==== 20A DC-DC + diode isolator: $173 ====
 This option is requires no HVD, but has two possible drawbacks:
@@ Line 68: / Line 69: @@
   - drop of ~0.5v.  Perhaps not a big issue since the DC-DC is boosting.
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.  [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
+  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+  * [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
-==== 20A combo DC-DC + MOSFET isolator: $224 ====
+==== 20A DC-DC + MOSFET isolator: $224 ====
 Same technology as the Smartpass.
@@ Line 76: / Line 78: @@
 Similar to the diode isolator setup above, but with MOSFETS instead of diodes.  This means no((or minimal)) voltage drop.
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.  [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
+  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+  * [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
@@ Line 84: / Line 87: @@
 The main benefit of a separate MPPT is we get to normal PV input limits, 100v+.  We also may have more control.  One can also drastically reduce cost by using PWM with nominal 12v panels, or using MPPT with cheap used higher-voltage panels.
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80. [[https://amzn.to/3QGwihC|Cole-Hersee continuous duty solenoid]], $55. [[https://amzn.to/3AhdNti|High voltage disconnect]], $13.
+  * MPPT
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19. [[https://amzn.to/3QGwihC|Cole-Hersee continuous duty solenoid]], $55. [[https://amzn.to/3AhdNti|High voltage disconnect]], $13.
+    * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+    * [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80.
+    * [[https://amzn.to/3QGwihC|Cole-Hersee continuous duty solenoid]], $55.
+    * [[https://amzn.to/3AhdNti|High voltage disconnect]], $13.
+  * PWM
+    * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+    * [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19.
+    * [[https://amzn.to/3QGwihC|Cole-Hersee continuous duty solenoid]], $55.
+    * [[https://amzn.to/3AhdNti|High voltage disconnect]], $13.
-==== 20A DC-DC + 20A DC-DC + 20A solar controller + diode isolator: $192-$253 ====
+==== 20A DC-DC + 20A solar controller + diode isolator: $192-$253 ====
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80. [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
+  * MPPT
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19. [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
+      * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+      * [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80.
+      * [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
+  * PWM
+    * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+    * [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19.
+    * [[https://amzn.to/3T9JKft|Cole-Hersee 90A diode isolator]], $69.
-==== 20A DC-DC 20A DC-DC + 20A solar controller + MOSFET isolator: $243-$304 ====
+==== 20A DC-DC + 20A solar controller + MOSFET isolator: $243-$304 ====
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80. [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
+  * MPPT
+      * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
-  * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104. [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19. [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
+      * [[https://amzn.to/3Aj7NjP|EpEver 20A 100v MPPT]], $80.
+      * [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
+  * PWM
+    * [[https://amzn.to/3pCW5eY|Renogy 20A DC-DC]], $104.
+    * [[https://amzn.to/3PMlFIS|HQST 20A PWM]], $19.
+    * [[https://amzn.to/3wnJpfE|Victron ArgoFET 200A isolator]] (100A for each "leg", so both starter and house batt get  ≤100A).  $120.
 ==== 50A DC-DC combo chargers:  $265-$328 ====

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