What do you mean for the battery under the hood? I want to run 2 different types of batteries under the hood (1 starter and 1 deep cycle for the accessories). I was under the impression that running an isolator connecting 2 different types of batteries is bad.
Dissimilar Batteries
- Thread starter DiploStrat
- Start date
What do you mean for the battery under the hood? I want to run 2 different types of batteries under the hood (1 starter and 1 deep cycle for the accessories). I was under the impression that running an isolator connecting 2 different types of batteries is bad.
DiploStrat
Expedition Leader
Sorry; I was not that clear. What I mean is that you do not need to interpose any form of electronics between your truck and its starting battery unless you replace the starting battery with a battery that requires a totally different charging regime. As far as I can see, the gross differences are:
-- Calcium/FLA: Highest voltage - don't know about the current requirements, but in the case of my truck, I assume that GM is doing it right.
-- Open FLA: Next highest voltage - lower current
-- Sealed FLA (e.g., AGM): Lower voltage - highest current
-- Gel: Lowest voltage of all - don't know about current requirements
As far as I know, there is no problem in connecting a deep cycle and a starter battery, OF THE SAME TYPE, together, as with a solenoid. The trick comes in that the starter battery will be recharged relatively quickly, at which point the alternator may stop producing current, and thus not charge the deep cycle battery.
As a rule, twin diode isolators are the worst as they impose a voltage drop. In extreme cases, neither the starter nor the camper battery can ever receive a full charge.
Solenoid/relay systems are generally the best, in that they have the lowest loss. If the batteries are the same type, close enough, and connected by a large enough cable, then the system simply sees one large battery and handles it. (The starter battery will generally not overcharge because as soon as the batteries are put in parallel, the starter battery starts to discharge into the camper battery.)
The usual reason that a solenoid system does not achieve a full or fast charge is voltage drop, usually caused by too long a run of too small a wire. To charge properly, the charging voltage must be higher than the voltage of the battery being charged. So if your battery is discharged to say, 12v and you hit it with a charging voltage of say, 14.4v, then you will achieve a full charge as fast as you can pump in the amperes. But if your alternator is only putting out 13v and your big bank of camper batteries is 25 feet away at the end of a 6 AWG wire, then you may barely achieve 12.5v at the terminal of the camper battery. In this case you can drive all day and nothing will happen.
B2B products work by using a diode to avoid a drain from battery to battery. When the device switches on, then it takes current from the starter battery (not the alternator) and then increases the voltage as needed to charge the camper battery. It thus makes of the voltage loss from the diode, a virtue, as it can boost the voltage as needed, and then drop back to a lower float. And by placing the B2B close to the camper batteries (or by using a sense wire), the B2B compensates for any voltage drops. (Within reason, you can trade volts for amps and vice versa.) The only problem that I see with any of the B2B units is that they top out at under 50A.
So, in your case, if both your batteries are AGM and your truck is set up for AGM, you should be golden. If, however, your truck is set up for calcium/FLA (as mine is) and runs at over 15v, then you should not simply connect the AGM second battery, which probably wants less than 15v, to the starter battery. Under these circumstances, putting a B2B between the two batteries might work well.
Based on my experience with the A2B, I would want to be sure that I could return the unit if it did not perform in the real world.
I hope that this is:
a) Correct, and
b) Clear enough to be helpful.
As I said, I am blundering around in this wilderness myself.
-- Calcium/FLA: Highest voltage - don't know about the current requirements, but in the case of my truck, I assume that GM is doing it right.
-- Open FLA: Next highest voltage - lower current
-- Sealed FLA (e.g., AGM): Lower voltage - highest current
-- Gel: Lowest voltage of all - don't know about current requirements
As far as I know, there is no problem in connecting a deep cycle and a starter battery, OF THE SAME TYPE, together, as with a solenoid. The trick comes in that the starter battery will be recharged relatively quickly, at which point the alternator may stop producing current, and thus not charge the deep cycle battery.
As a rule, twin diode isolators are the worst as they impose a voltage drop. In extreme cases, neither the starter nor the camper battery can ever receive a full charge.
Solenoid/relay systems are generally the best, in that they have the lowest loss. If the batteries are the same type, close enough, and connected by a large enough cable, then the system simply sees one large battery and handles it. (The starter battery will generally not overcharge because as soon as the batteries are put in parallel, the starter battery starts to discharge into the camper battery.)
The usual reason that a solenoid system does not achieve a full or fast charge is voltage drop, usually caused by too long a run of too small a wire. To charge properly, the charging voltage must be higher than the voltage of the battery being charged. So if your battery is discharged to say, 12v and you hit it with a charging voltage of say, 14.4v, then you will achieve a full charge as fast as you can pump in the amperes. But if your alternator is only putting out 13v and your big bank of camper batteries is 25 feet away at the end of a 6 AWG wire, then you may barely achieve 12.5v at the terminal of the camper battery. In this case you can drive all day and nothing will happen.
B2B products work by using a diode to avoid a drain from battery to battery. When the device switches on, then it takes current from the starter battery (not the alternator) and then increases the voltage as needed to charge the camper battery. It thus makes of the voltage loss from the diode, a virtue, as it can boost the voltage as needed, and then drop back to a lower float. And by placing the B2B close to the camper batteries (or by using a sense wire), the B2B compensates for any voltage drops. (Within reason, you can trade volts for amps and vice versa.) The only problem that I see with any of the B2B units is that they top out at under 50A.
So, in your case, if both your batteries are AGM and your truck is set up for AGM, you should be golden. If, however, your truck is set up for calcium/FLA (as mine is) and runs at over 15v, then you should not simply connect the AGM second battery, which probably wants less than 15v, to the starter battery. Under these circumstances, putting a B2B between the two batteries might work well.
Based on my experience with the A2B, I would want to be sure that I could return the unit if it did not perform in the real world.
I hope that this is:
a) Correct, and
b) Clear enough to be helpful.
As I said, I am blundering around in this wilderness myself.
Last edited:
pappawheely
Autonomous4X4
Good info, thanks.
Thnx Diplo.
My first set of (2) batteries will be under the hood so I will probably just go with a simple National Luna or IBS setup (run a starter battery as the primary and a deep cycle of the same size and brand (both AGM))
My second auxiliary battery will be in the rear cargo area and won't need to ever "boost" the primary starter battery so that one will have a DC-DC charger (located right at the auxiliary battery to account for voltage drops from the front of the Jeep and the rear-mounted battery).
Thanks for the info.
My first set of (2) batteries will be under the hood so I will probably just go with a simple National Luna or IBS setup (run a starter battery as the primary and a deep cycle of the same size and brand (both AGM))
My second auxiliary battery will be in the rear cargo area and won't need to ever "boost" the primary starter battery so that one will have a DC-DC charger (located right at the auxiliary battery to account for voltage drops from the front of the Jeep and the rear-mounted battery).
Thanks for the info.