Bear with me on this --- it is a boat post, but my opening paragraph with the background, might not seem that way.
I ran down the 2-year old 35 AH AGM auxilary 12V battery ex my 2001 Prius a few months ago by leaving the key on overnight turned to the "ignition" mode. The battery charged up again just fine, but the Prius' on-board computer system is very particular. If it senses that the 12V battery needs topping off, then the gas engine starts up to charge it. Compared to a fresh battery, the engine would often start up while waiting at a stoplight to charge the 12V battery. No longer as fuel miserly as it should be. So I got a new AGM for the Prius. Really could have gotten by with the old one since the cost of the new AGM is probably several years of gas savings realized by the new one. But I had an ulterier motive.
I took the 2-year old AGM to the boat, disconnected the battery cables from my #1 house bank battery and reconnected them to the AGM from the Prius. The little battery cranked over the engine strongly. Even after a two bursts of 5 second fuel starved cranking (more than enough time since the engine always starts in one-two seconds), the AGM's voltage was still at 12.7-12.8 volts. So the AGM would seem to be great for an emergency starting battery. I'll keep it topped off ex one of my two solar panel charge controllers by installing an A/B switch to direct the charge current periodically from the house bank to the AGM. Since AGM's are very slow at self discharging, just a few days of solar every couple of weeks or so should keep it in good condition, I would expect.
So now to the questions which will help me with the wiring. Since using an emergency starting battery should be an infrequent event, I want to keep it simple and low cost (but needs to be safe):
- If/When this AGM is ever used in an emergency, and given that its AH rating is small relative to a depleted deep-cycle house battery, will I need to configure so that the AGM is not connected to the deep-cycle cable without first disconnecting the house battery? It would seem to me that unless the AGM and the house bank are isolated, the depleted house batteries would suck power out of the AGM as they seek to recharge. Then maybe not enough cranking voltage to start the engine.
- If (say) its the house battery #1 red cable that is disconnected (or de-switched) for directing instead to the AGM, I'll put the main battery switch over to #1. After the engine is started, I will want the altenator to recharge the depleted house batteries. But first, I will need to move the main switch to battery #2. Then I can move the cable from the AGM back to house battery #1. Finally I move the main switch to "Both" for the altenator to charge both batteries. This sequence must be adhered to because if the cable is removed from the AGM with the switch still in the #1 position, then the altenator will see no load. There go the diodes? I can see the need to prepare a sequence check list for referal.
Thanks fo comments, warnings and ideas.
I ran down the 2-year old 35 AH AGM auxilary 12V battery ex my 2001 Prius a few months ago by leaving the key on overnight turned to the "ignition" mode. The battery charged up again just fine, but the Prius' on-board computer system is very particular. If it senses that the 12V battery needs topping off, then the gas engine starts up to charge it. Compared to a fresh battery, the engine would often start up while waiting at a stoplight to charge the 12V battery. No longer as fuel miserly as it should be. So I got a new AGM for the Prius. Really could have gotten by with the old one since the cost of the new AGM is probably several years of gas savings realized by the new one. But I had an ulterier motive.
I took the 2-year old AGM to the boat, disconnected the battery cables from my #1 house bank battery and reconnected them to the AGM from the Prius. The little battery cranked over the engine strongly. Even after a two bursts of 5 second fuel starved cranking (more than enough time since the engine always starts in one-two seconds), the AGM's voltage was still at 12.7-12.8 volts. So the AGM would seem to be great for an emergency starting battery. I'll keep it topped off ex one of my two solar panel charge controllers by installing an A/B switch to direct the charge current periodically from the house bank to the AGM. Since AGM's are very slow at self discharging, just a few days of solar every couple of weeks or so should keep it in good condition, I would expect.
So now to the questions which will help me with the wiring. Since using an emergency starting battery should be an infrequent event, I want to keep it simple and low cost (but needs to be safe):
- If/When this AGM is ever used in an emergency, and given that its AH rating is small relative to a depleted deep-cycle house battery, will I need to configure so that the AGM is not connected to the deep-cycle cable without first disconnecting the house battery? It would seem to me that unless the AGM and the house bank are isolated, the depleted house batteries would suck power out of the AGM as they seek to recharge. Then maybe not enough cranking voltage to start the engine.
- If (say) its the house battery #1 red cable that is disconnected (or de-switched) for directing instead to the AGM, I'll put the main battery switch over to #1. After the engine is started, I will want the altenator to recharge the depleted house batteries. But first, I will need to move the main switch to battery #2. Then I can move the cable from the AGM back to house battery #1. Finally I move the main switch to "Both" for the altenator to charge both batteries. This sequence must be adhered to because if the cable is removed from the AGM with the switch still in the #1 position, then the altenator will see no load. There go the diodes? I can see the need to prepare a sequence check list for referal.
Thanks fo comments, warnings and ideas.